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w wm8988 stereo codec for portable audio applications wolfson microelectronics plc to receive regular email updates, sign up at http://www.wolfsonmicro.com/enews/ production data, october 2008, rev 4.0 copyright ? 2008 wolfson microelectronics plc description the wm8988 is a low power, high quality stereo codec designed for portable digital audio applications. the device integrates complete interfaces to 2 stereo headphone or line out ports. external component requirements are drastically reduced as no separate headphone amplifiers are required. advanced on-chip digital signal processing performs graphic equaliser, 3-d sound enhancement and automatic level control for the microphone or line input. the wm8988 can operate as a master or a slave, with various master clock frequencies including 12 or 24mhz for usb devices, or standard 256f s rates like 12.288mhz and 24.576mhz. different audio sample rates such as 96khz, 48khz, 44.1khz are generated directly from the master clock without the need for an external pll. the wm8988 operates at supply voltages down to 1.8v, although the digital core can operate at voltages down to 1.42v to save power, and the maximum for all supplies is 3.6 volts. different sections of the chip can also be powered down under software control. the wm8988 is supplied in a very small and thin 4x4mm col package, ideal for use in hand-held and portable systems. features ? dac snr 100db (?a? weighted), thd ?90db at 48khz, 3.3v ? adc snr 93db (?a? weighted), thd -81db at 48khz, 3.3v ? programmable alc / noise gate ? 2x on-chip headphone drivers - >40mw output power on 16 ? / 3.3v - thd ?80db at 20mw, snr 90db with 16 ? load ? digital graphic equaliser ? low power - 7mw stereo playback (1.8v / 1.5v supplies) - 14mw record and playback (1.8v / 1.5v supplies) ? low supply voltages - analogue 1.8v to 3.6v - digital core: 1.42v to 3.6v - digital i/o: 1.8v to 3.6v ? 256fs / 384fs or usb master clock rates: 12mhz, 24mhz ? audio sample rates: 8, 11.025, 16, 22.05, 24, 32, 44.1, 48, 88.2, 96khz generated internally from master clock ? 4x4mm col package applications ? portable multimedia players ? multimedia handsets ? handheld gaming block diagram csb sdin sclk mode vref avdd agnd vmid adcdat bclk mclk dacdat lrc
wm8988 production data w pd, rev 4.0, october 2008 2 table of contents description .......................................................................................................1 features.............................................................................................................1 applications .....................................................................................................1 block diagram .................................................................................................1 table of contents .........................................................................................2 pin configuration and device marking..................................................3 ordering information ..................................................................................3 pin description ................................................................................................4 absolute maximum ratings.........................................................................5 recommended operation conditions .....................................................5 electrical characteristics ......................................................................6 power consumption ....................................................................................10 signal timing requirements .....................................................................11 system clock timing............................................................................................ 11 audio interface timing ? master mode ......................................................... 11 audio interface timing ? slave mode ............................................................ 12 internal power on reset circuit ..........................................................15 device description .......................................................................................16 introduction.......................................................................................................... 16 input signal path.................................................................................................. 16 automatic level control (alc) ....................................................................... 22 output signal path.............................................................................................. 26 analogue outputs ............................................................................................... 31 enabling the outputs ......................................................................................... 33 thermal shutdown .............................................................................................. 33 digital audio interface...................................................................................... 34 audio interface control .................................................................................. 37 clocking and sample rates .............................................................................. 39 control interface .............................................................................................. 41 power supplies ..................................................................................................... 42 power management ............................................................................................. 42 register map...................................................................................................46 digital filter characteristics ...............................................................47 terminology........................................................................................................... 47 dac filter responses ......................................................................................... 48 adc filter responses ......................................................................................... 49 de-emphasis filter responses ........................................................................ 50 highpass filter ..................................................................................................... 51 applications information .........................................................................52 recommended external components........................................................... 52 line input configuration................................................................................... 53 headphone output configuration ................................................................ 53 line output configuration............................................................................... 53 minimising pop noise at the analogue outputs ........................................ 54 power management examples ......................................................................... 54 package dimensions ....................................................................................55 important notice ..........................................................................................56 address.................................................................................................................... 56
production data wm8988 w pd, rev 4.0, october 2008 3 pin configuration and device marking ordering information order code temperature range package moisture sensitivity level peak soldering temperature wm8988lgecn/v -25c to +85c 28-lead col qfn (4x4x0.55mm, lead-free) msl3 260c wm8988lgecn/rv -25c to +85c 28-lead col qfn (4x4x0.55mm, lead-free) tape and reel msl3 260c note: reel quantity = 3,500
wm8988 production data w pd, rev 4.0, october 2008 4 pin description pin no name type description 1 mclk digital input master clock 2 dcvdd supply digital core supply 3 dbvdd supply digital buffer (i/o) supply 4 dgnd supply digital ground (return path for both dcvdd and dbvdd) 5 bclk digital input / output audio interface bit clock 6 dacdat digital input dac digital audio data 7 lrc digital input / output audio interface left / right clock 8 adcdat digital output adc digital audio data 9 hpcom analogue input lout1 and rout1 common mode feedback 10 lcom analogue input lout2 and rout2 common mode feedback 11 rout1 analogue output right output 1 (line or headphone) 12 lout1 analogue output left output 1 (line or headphone) 13 hpgnd supply supply for analogue output drivers (lout1/2, rout1/2) 14 rout2 analogue output right output 1 (line or headphone ) 15 lout2 analogue output left output 1 (line or headphone) 16 hpvdd supply supply for analogue output drivers (lout1/2, rout1/2, monout) 17 avdd supply analogue supply 18 agnd supply analogue ground (return path for avdd) 19 vref analogue output reference voltage decoupling capacitor 20 vmid analogue output midrail voltage decoupling capacitor 21 rinput2 analogue input right channel input 2 22 linput2 analogue input left channel input 2 23 rinput1 analogue input right channel input 1 24 linput1 analogue input left channel input 1 25 mode digital input control interface selection 26 csb digital input chip select / device address selection 27 sdin digital input/output control interface data input / 2-wire acknowledge output 28 sclk digital input control interface clock input
production data wm8988 w pd, rev 4.0, october 2008 5 absolute maximum ratings absolute maximum ratings are stress ratings only. permanent damage to the device may be caused by continuously operating at or beyond these limits. device functional operating limits and guaranteed performance specifications are given under electrical characteristics at the test conditions specified. esd sensitive device. this device is manufactured on a cmos process. it is therefore generically susceptible to damage from excessive static voltages. proper esd precautions must be taken during handling and storage of this device. wolfson tests its package types according to ipc/jedec j-std-020b for moisture sensitivity to determine acceptable storage conditions prior to surface mount assembly. these levels are: msl1 = unlimited floor life at <30 c / 85% relative humidity. not normally stored in moisture barrier bag. msl2 = out of bag storage for 1 year at <30 c / 60% relative humidity. supplied in moisture barrier bag. msl3 = out of bag storage for 168 hours at <30 c / 60% relative humidity. supplied in moisture barrier bag. the moisture sensitivity level for each package type is specified in ordering information. condition min max supply voltages -0.3v +4.5v voltage range digital inputs dgnd -0.3v dbvdd +0.3v voltage range analogue inputs agnd -0.3v avdd +0.3v operating temperature range, t a -25 c +85 c storage temperature after soldering -65 c +150 c notes 1. analogue and digital grounds must always be within 0.3v of each other. 2. all digital and analogue supplies are completely independent from each other. 3. dcvdd must be less than or equal to avdd and dbvdd. recommended operation conditions parameter symbol min typ max unit digital supply range (core) dcvdd 1.42 3.6 v digital supply range (buffer) dbvdd 1.7 3.6 v analogue supplies range avdd, hpvdd 1.8 3.6 v ground dgnd,agnd, hpgnd 0 v
wm8988 production data w pd, rev 4.0, october 2008 6 electrical characteristics test conditions dcvdd = 1.5v, dbvdd = 2.4v, avdd = hpvdd =2.4v , t a = +25 o c, 1khz signal, fs = 48khz, pga gain = 0db, 24-bit audio data unless otherwise stated. parameter symbol test conditions min typ max unit analogue inputs (linput1, rinput1, linput2, rinput2) to adc out avdd = 3.3v 0.95 1.0 1.05 avdd = 2.4v 0.690 0.727 0.763 full scale input signal level (for adc 0db input at 0db gain) v infs avdd = 1.8v 0.480 0.545 0.610 vrms l/rinput1 to adc, pga gain = 0db 16 22 l/rinput1 to adc, pga gain = +30db 1.5 2.8 l/rinput2 to adc pga gain = 0db 16 22 input resistance r in l/rinput2 to adc pga gain = 30db 1.5 2.8 k ? input capacitance 10 pf avdd = 3.3v 80 93 avdd = 2.4v 80 88 signal to noise ratio (a-weighted) snr avdd = 1.8v 78 87 db -1dbfs input, avdd = 3.3v -81 -68 -1dbfs input, avdd = 2.4v -80 -68 total harmonic distortion thd -1dbfs input, avdd = 1.8v -76 -65 db -1dbfs input, avdd = 3.3v -75 -65 -1dbfs input, avdd = 2.4v -70 -65 total harmonic distortion + noise thd+n -1dbfs input, avdd = 1.8v -70 -60 db 1khz signal 85 adc channel separation 10khz signal 85 db channel matching 1khz signal -0.5 0.2 +0.5 db analogue outputs (lout1/2, rout1/2) avdd = 3.3v 0.95 1.0 1.05 avdd = 2.4v 0.690 0.727 0.763 0db full scale output voltage v outfs avdd = 1.8v 0.507 0.545 0.583 vrms mute attenuation 1khz, full scale signal 90 db 1khz signal 85 channel separation 10khz signal 85 db pga gain range guaranteed monotonic +6 -67 db pga step size 0.25 1 1.25 db
production data wm8988 w pd, rev 4.0, october 2008 7 test conditions dcvdd = 1.5v, dbvdd = 2.4v, avdd = hpvdd =2.4v , t a = +25 o c, 1khz signal, fs = 48khz, pga gain = 0db, 24-bit audio data unless otherwise stated. parameter symbol test conditions min typ max unit dac to line-out (l/rout1 or l/rout2 with 10k ? / 50pf load) dacmixbias=0 88 100 avdd=3.3v hpcom=lc om=0 dacmixbias=1 99 dacmixbias=0 97 a vdd = 2.4v hpcom=lc om=1 dacmixbias=1 88 96 dacmixbias=0 96 signal to noise ratio (a-weighted) snr avdd=1.8v hpcom=lc om=0 dacmixbias=1 85 95 db dacmixbias=0 -90 -75 avdd=3.3v hpcom=lc om=0 dacmixbias=1 -89 dacmixbias=0 -83 a vdd = 2.4v hpcom=lc om=1 dacmixbias=1 -82 -75 dacmixbias=0 -80 total harmonic distortion thd avdd=1.8v hpcom=lc om=0 dacmixbias=1 -79 -65 db dacmixbias=0 -88 -70 avdd=3.3v hpcom=lc om=0 dacmixbias=1 -87 dacmixbias=0 -75 a vdd = 2.4v hpcom=lc om=1 dacmixbias=1 -74 -70 dacmixbias=0 -75 total harmonic distortion + noise thd+n avdd=1.8v hpcom=lc om=0 dacmixbias=1 -74 -65 db 1khz signal 100 channel separation 10khz signal 85 db db ground noise rejection 10mv, 20khz noise on lcom/hpcom, lcom/hpcom enabled 40 db headphone output (lout1/rout1, lout2/rout2 ac coupled to load) output power per channel p o output power is very closely correlated with thd; see below. hpvdd=1.8v, r l =32 ? p o =5mw hpcom=lcom=0 dacmixbias=1 0.013 -78 % db hpvdd=1.8v, r l =16 ? p o =5mw hpcom=lcom=0 dacmixbias=1 0.010 -80 hpvdd=2.4v, r l =32 ? , p o =5mw hpcom=lcom=1 dacmixbias=1 0.010 -80 total harmonic distortion thd hpvdd=2.4v, r l =16 ? , p o =5mw hpcom=lcom=1 dacmixbias=1 0.013 -78 0.032 -70
wm8988 production data w pd, rev 4.0, october 2008 8 test conditions dcvdd = 1.5v, dbvdd = 2.4v, avdd = hpvdd =2.4v , t a = +25 o c, 1khz signal, fs = 48khz, pga gain = 0db, 24-bit audio data unless otherwise stated. parameter symbol test conditions min typ max unit hpvdd=3.3v, r l =32 ? , p o =20mw hpcom=lcom=0 dacmixbias=0 0.010 -82 hpvdd=3.3v, r l =16 ? , p o =20mw hpcom=lcom=0 dacmixbias=0 0.010 -80 hpvdd=1.8v, r l =32 ? p o =5mw hpcom=lcom=0 dacmixbias=1 -80 db hpvdd=1.8v, r l =16 ? p o =5mw hpcom=lcom=0 dacmixbias=1 -78 hpvdd=2.4v, r l =32 ? , p o =5mw hpcom=lcom=1 dacmixbias=1 -79 hpvdd=2.4v, r l =16 ? , p o =5mw hpcom=lcom=1 dacmixbias=1 -77 -65 hpvdd=3.3v, r l =32 ? , p o =20mw hpcom=lcom=0 dacmixbias=0 -80 total harmonic distortion + noise thd+n hpvdd=3.3v, r l =16 ? , p o =20mw hpcom=lcom=0 dacmixbias=0 -78 hpvdd = 3.3v hpcom=lcom=0 dacmixbias=1 100 db hpvdd = 2.4v hpcom=lcom=1 dacmixbias=1 90 96 signal to noise ratio (a-weighted) snr hpvdd = 1.8v hpcom=lcom=0 dacmixbias=0 96 headphone output ground noise rejection 10mv, 20khz noise on hpcom, hpcom enabled 40 db line output ground noise rejection 10mv, 20khz noise on lcom, lcom enabled 40 db analogue reference levels midrail reference voltage vmid ?3% avdd/2 +3% v buffered reference voltage vref ?3% avdd/2 +3% v digital input / output input high level v ih 0.7 db vdd v input low level v il 0.3 dbvdd v
production data wm8988 w pd, rev 4.0, october 2008 9 test conditions dcvdd = 1.5v, dbvdd = 2.4v, avdd = hpvdd =2.4v , t a = +25 o c, 1khz signal, fs = 48khz, pga gain = 0db, 24-bit audio data unless otherwise stated. parameter symbol test conditions min typ max unit output high level v oh i oh = +1ma 0.9 db vdd v output low level v ol i ol = -1ma 0.1 dbvdd v
wm8988 production data w pd, rev 4.0, october 2008 10 power consumption the power consumption of the wm8988 depends on the following factors. ? supply voltages: reducing the supply voltages also reduces supply currents, and therefore results in significant power savings, especially in the digital sections of the wm8988. ? operating mode: significant power savings can be achieved by always disabling parts of the wm8988 that are not used (e.g. mic pre-amps, unused outputs, dac, adc, etc.) scenario detail avdd power (mw) hpvdd power (mw) dcvdd power (mw) dbvdd power (mw) total power (mw) off clocks stopped 0.001 0.000 0.012 0.000 0.01 playback to lineout 0db 1khz sinusoid 4.9 1.2 4.8 0.4 11.3 playback to headphone 32ohm quiescent no signal 4.7 1.0 4.7 0.4 10.3 playback to headphone 32ohm -50db (near silence) 1khz sinusoid 4.6 1.1 4.8 0.4 10.9 playback to headphone 32ohm -21db (0.1mw/channel) 1khz sinusoid 4.6 4.9 4.8 0.4 14.7 playback to headphone 32ohm -9db (2mw/channel) 1khz sinusoid 4.6 17.7 4.8 0.4 27.5 table 1 power consumption for 2.4v / 1.8v supplies scenario detail avdd power (mw) hpvdd power (mw) dcvdd power (mw) dbvdd power (mw) total power (mw) off clocks stopped 0.001 0.000 0.013 0.000 0.01 playback to lineout 0db 1khz sinusoid 7.6 2.0 4.9 0.4 14.9 playback to headphone 32ohm quiescent no signal 7.6 1.8 4.9 0.4 14.7 playback to headphone 32ohm -50db (near silence) 1khz sinusoid 7.6 1.8 4.8 0.4 14.6 playback to headphone 32ohm -24db (0.1mw/channel) 1khz sinusoid 7.6 5.9 4.8 0.4 18.7 playback to headphone 32ohm -11db (2mw/channel) 1khz sinusoid 7.6 22.3 4.8 0.4 35.1 table 2 power consumption for 3.0v / 1.8v supplies notes: 1. all figures are at t a = +25 o c, slave mode, fs = 48khz, mclk = 12.288 mhz (256fs), 2. the power dissipated in the headphone is not included in the above table.
production data wm8988 w pd, rev 4.0, october 2008 11 signal timing requirements system clock timing mclk t mclkl t mclkh t mclky figure 1 system clock timing requirements test conditions clkdiv2=0 , dcvdd = 1.42v, dbvdd = 3.3v, dgnd = 0v, t a = +25 o c, slave mode fs = 48khz, mclk = 384fs, 24-bit data, unless otherwise stated. parameter symbol min typ max unit system clock timing information mclk system clock pulse width high t mclkl 21 ns mclk system clock pulse width low t mclkh 21 ns mclk system clock cycle time t mclky 54 ns mclk duty cycle t mclkds 60:40 40:60 test conditions clkdiv2=1 , dcvdd = 1.42v, dbvdd = 3.3v, dgnd = 0v, t a = +25 o c, slave mode fs = 48khz, mclk = 384fs, 24-bit data, unless otherwise stated. parameter symbol min typ max unit system clock timing information mclk system clock pulse width high t mclkl 10 ns mclk system clock pulse width low t mclkh 10 ns mclk system clock cycle time t mclky 27 ns audio interface timing ? master mode figure 2 digital audio data timing ? master mode bclk (output) adcdat lrc (output) t dl dacdat t dda t dht t dst
wm8988 production data w pd, rev 4.0, october 2008 12 test conditions dcvdd = 1.42v, dbvdd = 3.3v, dgnd = 0v, t a = +25 o c, slave mode, fs = 48khz, mclk = 256fs, 24-bit data, unless otherwise stated. parameter symbol min typ max unit bit clock timing information bclk rise time (10pf load) t bclkr 3 ns bclk fall time (10pf load) t bclkf 3 ns bclk duty cycle (normal mode, bclk = mclk/n) t bclkds 50:50 bclk duty cycle (usb mode, bclk = mclk) t bclkds t mclkds audio data input timing information daclrc propagation delay from bclk falling edge t dl 10 ns adcdat propagation delay from bclk falling edge t dda 10 ns dacdat setup time to bclk rising edge t dst 10 ns dacdat hold time from bclk rising edge t dht 10 ns audio interface timing ? slave mode figure 3 digital audio data timing ? slave mode test conditions dcvdd = 1.42v, dbvdd = 3.3v, dgnd = 0v, t a = +25 o c, slave mode, fs = 48khz, mclk = 256fs, 24-bit data, unless otherwise stated. parameter symbol min typ max unit audio data input timing information bclk cycle time t bcy 50 ns bclk pulse width high t bch 20 ns bclk pulse width low t bcl 20 ns daclrc set-up time to bclk rising edge t lrsu 10 ns daclrc hold time from bclk rising edge t lrh 10 ns dacdat hold time from bclk rising edge t dh 10 ns adcdat propagation delay from bclk falling edge t dd 10 ns note: bclk period should always be greater than or equal to mclk period. bclk lrc t bch t bcl t bcy dacdat adcdat t lrsu t ds t lrh t dh t dd
production data wm8988 w pd, rev 4.0, october 2008 13 control interface timing ? 3-wire mode csb sclk sdin t csl t dho t dsu t csh t scy t sch t scl t scs lsb t css figure 4 control interface timing ? 3-wire serial control mode test conditions dcvdd = 1.42v, dbvdd = 3.3v, dgnd = 0v, t a = +25 o c, slave mode, fs = 48khz, mclk = 256fs, 24-bit data, unless otherwise stated. parameter symbol min typ max unit program register input information sclk rising edge to csb rising edge t scs 80 ns sclk pulse cycle time t scy 200 ns sclk pulse width low t scl 80 ns sclk pulse width high t sch 80 ns sdin to sclk set-up time t dsu 40 ns sclk to sdin hold time t dho 40 ns csb pulse width low t csl 40 ns csb pulse width high t csh 40 ns csb rising to sclk rising t css 40 ns pulse width of spikes that will be suppressed t ps 0 5 ns
wm8988 production data w pd, rev 4.0, october 2008 14 control interface timing ? 2-wire mode sdin sclk t 3 t 1 t 6 t 2 t 7 t 5 t 4 t 3 t 8 t 9 figure 5 control interface timing ? 2-wire serial control mode test conditions dcvdd = 1.42v, dbvdd = 3.3v, dgnd = 0v, t a = +25 o c, slave mode, fs = 48khz, mclk = 256fs, 24-bit data, unless otherwise stated. parameter symbol min typ max unit program register input information sclk frequency 0 526 khz sclk low pulse-width t 1 1.3 us sclk high pulse-width t 2 600 ns hold time (start condition) t 3 600 ns setup time (start condition) t 4 600 ns data setup time t 5 100 ns sdin, sclk rise time t 6 300 ns sdin, sclk fall time t 7 300 ns setup time (stop condition) t 8 600 ns data hold time t 9 900 ns pulse width of spikes that will be suppressed t ps 0 5 ns
production data wm8988 w pd, rev 4.0, october 2008 15 internal power on reset circuit vdd t1 gnd avdd dcvdd dgnd internal porb power on reset circuit figure 6 internal power on reset circuit schematic the wm8988 includes an internal power-on-reset circuit, as shown in figure 6, which is used to reset the digital logic into a default state after power up. the power on reset circuit is powered from dcvdd and monitors dcvdd and avdd. it asserts porb low if dcvdd or avdd are below a minimum threshold. figure 7 typical power-up sequence figure 7 shows a typical power-up sequence. when dcvdd and avdd rise above the minimum thresholds, vpord_dcvdd and vpord_avdd, there is enough voltage for the circuit to guarantee the power on reset is asserted low and the chip is held in reset. in this condition, all writes to the control interface are ignored. when dcvdd rises to vpor_dcvdd_on and avdd rises to vpor_avdd_on, porb is released high and all registers are in their default state and writes to the control interface may take place. if dcvdd and avdd rise at different rates then porb will only be released when dcvdd and avdd have both exceeded the vpor_dcvdd_on and vpor_avdd_on thresholds. on power down, porb is asserted low whenever dcvdd drops below the minimum threshold vpor_dcvdd_off or avdd drops below the minimum threshold vpor_avdd_off. symbol min typ max unit v pord_dcvdd 0.4 0.6 0.8 v v por_dcvdd_on 0.9 1.26 1.6 v v por_avdd_on 0.5 0.7 0.9 v v por_avdd_off 0.4 0.6 0.8 v table 3 typical por operation (typical values, not tested)
wm8988 production data w pd, rev 4.0, october 2008 16 device description introduction the wm8988 is a low power audio codec offering a combination of high quality audio, advanced features, low power and small size. these characteristics make it ideal for portable digital audio applications such as mp3 and minidisk player / recorders. stereo 24-bit multi-bit delta sigma adcs and dacs are used with oversampling digital interpolation and decimation filters. the device includes three stereo analogue inputs that can be switched internally. each can be used as either a line level input or microphone input and linput1/rinput1 and linput2/rinput2 can be configured as mono differential inputs. a programmable gain amplifier with automatic level control (alc) keeps the recording volume constant. the on-chip stereo adc and dac are of a high quality using a multi-bit, low-order oversampling architecture to deliver optimum performance with low power consumption. the dac output signal first enters an analogue mixer where an analogue input and/or the post-alc signal can be added to it. this mix is available on line and headphone outputs. the wm8988 has a configurable digital audio interface where adc data can be read and digital audio playback data fed to the dac. it supports a number of audio data formats including i 2 s, dsp mode (a burst mode in which frame sync plus 2 data packed words are transmitted), msb-first, left justified and and can operate in master or slave modes. the wm8988 uses a unique clocking scheme that can generate many commonly used audio sample rates from either a 12.00mhz usb clock or an industry standard 256/384 f s clock. this feature eliminates the common requirement for an external phase-locked loop (pll) in applications where the master clock is not an integer multiple of the sample rate. sample rates of 8khz, 11.025khz, 12khz, 16khz, 22.05khz, 24khz, 32khz, 44.1khz, 48khz, 88.2khz and 96khz can be generated. the digital filters used for recording and playback are optimised for each sampling rate used. to allow full software control over all its features, the wm8988 offers a choice of 2 or 3 wire mpu control interface. it is fully compatible and an ideal partner for a wide range of industry standard microprocessors, controllers and dsps. the design of the wm8988 has given much attention to power consumption without compromising performance. it operates at very low voltages, and includes the ability to power off parts of the circuitry under software control, including standby and power off modes. input signal path the input signal path for each channel consists of a switch to select between three analogue inputs, followed by a pga (programmable gain amplifier) and an optional microphone gain boost. a differential input of either (linput1 ? rinput1) or (linput2 ? rinput2) may also be selected. the gain of the pga can be controlled either by the user or by the on-chip alc function (see automatic level control). the signal then enters an adc where it is digitised. alternatively, the two channels can also be mixed in the analogue domain and digitised in one adc while the other adc is switched off. the mono-mix signal appears on both digital output channels. signal inputs the wm8988 has two sets of high impedance, low capacitance ac coupled analogue inputs, linput1/rinput1 and linput2/rinput2. inputs can be configured as microphone or line level by enabling or disabling the microphone gain boost. linsel and rinsel control bits (see table 4) are used to select independently between external inputs and internally generated differential products (linput1-rinput1 or linput2-rinput2). the choice of differential signal, linput1-rinput1 or linput2-rinput2 is made using ds (refer to table 6). as an example, the wm8988 can be set up to convert one differential and one single ended mono signal by applying the differential signal to linput1/rinput1 and the single ended signal to rinput2. by setting linsel to l-r differential (see table 4), ds to linput1 ? rinput1 (see table 6) and rinsel to rinput2, each mono signal can then be routed to a separate adc or bypass path.
production data wm8988 w pd, rev 4.0, october 2008 17 the signal inputs are biased internally to the reference voltage vref. whenever the line inputs are muted or the device placed into standby mode, the inputs are kept biased to vref using special anti-thump circuitry. this reduces any audible clicks that may otherwise be heard when changing inputs. dc measurement for dc measurements (for example, battery voltage monitoring), the input signal at the linput1 and/or rinput1 pins can be taken directly into the respective adc, bypassing both pga and microphone boost. the adc output then becomes unsigned relative to avdd, instead of being a signed (two?s complement) number relative to vref. setting l/rdcm will override l/rinsel. the input range for dc measurement is agnd to avdd. register address bit label default description 7:6 linsel 00 left channel input select 00 = linput1 01 = linput2 10 = reserved 11 = l-r differential (either linput1- rinput1 or linput2-rinput2, selected by ds) r32 (20h) adc signal path control (left) 5:4 lmicboost 00 left channel microphone gain boost 00 = boost off (bypassed) 01 = 13db boost 10 = 20db boost 11 = 29db boost 7:6 rinsel 00 right channel input select 00 = rinput1 01 = rinput2 10 = reserved 11 = l-r differential (either linput1- rinput1 or linput2-rinput2, selected by ds) r33 (21h) adc signal path control (right) 5:4 rmicboost 00 right channel microphone gain boost 00 = boost off (bypassed) 01 = 13db boost 10 = 20db boost 11 = 29db boost table 4 input software control register address bit label default description 5 rdcm 0 right channel dc measurement 0 = normal operation, pga enabled 1 = measure dc level on rinput1 r31 (1fh) adc input mode 4 ldcm 0 left channel dc measurement 0 = normal operation, pga enabled 1 = measure dc level on linput1 table 5 dc measurement select register address bit label default description r31 (1fh) adc input mode 8 ds 0 differential input select 0: linput1 ? rinput1 1: linput2 ? rinput2 table 6 differential input select
wm8988 production data w pd, rev 4.0, october 2008 18 mono mixing the stereo adc can operate as a stereo or mono device, or the two channels can be mixed to mono, either in the analogue domain (i.e. before the adc) or in the digital domain (after the adc). monomix selects the mode of operation. for analogue mono mix either the left or right channel adc can be used, allowing the unused adc to be powered off or used for a dc measurement conversion. the user also has the flexibility to select the data output from the audio interface using datsel. the default is for left and right channel adc data to be output, but the interface may also be configured so that e.g. left channel adc data is output as both left and right data for when an analogue mono mix is selected. note: if dc measurement is selected this overrides the monomix selection. register address bit label default description r31 (1fh) adc input mode 7:6 monomix [1:0] 00 00: stereo 01: analogue mono mix (using left adc) 10: analogue mono mix (using right adc) 11: digital mono mix table 7 mono mixing register address bit label default description r23 (17h) additional control (1) 3:2 datsel [1:0] 00 00: left data=left adc; right data =right adc 01: left data =left adc; right data = left adc 10: left data = right adc; right data =right adc 11: left data = right adc; right data = left adc table 8 adc data output configuration pga control the pga matches the input signal level to the adc input range. the pga gain is logarithmically adjustable from +30db to ?17.25db in 0.75db steps. each pga can be controlled either by the user or by the alc function (see automatic level control). when alc is enabled for one or both channels, then writing to the corresponding pga control register has no effect. the gain is independently adjustable on both right and left line inputs. additionally, by controlling the register bits livu and rivu, the left and right gain settings can be simultaneously updated. setting the lzcen and rzcen bits enables a zero-cross detector which ensures that pga gain changes only occur when the signal is at zero, eliminating any zipper noise. if zero cross is enabled a timeout is also available to update the gain if a zero cross does not occur. this function may be enabled by setting toen in register r23 (17h). the inputs can also be muted in the analogue domain under software control. the software control registers are shown in table 9. if zero crossing is enabled, it is necessary to enable zero cross timeout to un-mute the input pgas. this is because their outputs will not cross zero when muted. alternatively, zero cross can be disabled before sending the un-mute command.
production data wm8988 w pd, rev 4.0, october 2008 19 register address bit label default description 8 livu 0 left volume update 0 = store linvol in intermediate latch (no gain change) 1 = update left and right channel gains (left = linvol, right = intermediate latch) 7 linmute 1 left channel input analogue mute 1 = enable mute 0 = disable mute note: livu must be set to un-mute. 6 lzcen 0 left channel zero cross detector 1 = change gain on zero cross only 0 = change gain immediately r0 (00h) left channel pga 5:0 linvol [5:0] 010111 ( 0db ) left channel input volume control 111111 = +30db 111110 = +29.25db . . 0.75db steps down to 000000 = -17.25db 8 rivu 0 right volume update 0 = store rinvol in intermediate latch (no gain change) 1 = update left and right channel gains (right = rinvol, left = intermediate latch) 7 rinmute 1 right channel input analogue mute 1 = enable mute 0 = disable mute note: rivu must be set to un-mute. 6 rzcen 0 right channel zero cross detector 1 = change gain on zero cross only 0 = change gain immediately r1 (01h) right channel pga 5:0 rinvol [5:0] 010111 ( 0db ) right channel input volume control 111111 = +30db 111110 = +29.25db . . 0.75db steps down to 000000 = -17.25db r23 (17h) additional control (1) 0 toen 0 timeout enable 0 : timeout disabled 1 : timeout enabled table 9 input pga software control
wm8988 production data w pd, rev 4.0, october 2008 20 analogue to digital converter (adc) the wm8988 uses a multi-bit, oversampled sigma-delta adc for each channel. the use of multi-bit feedback and high oversampling rates reduces the effects of jitter and high frequency noise. the adc full scale input level is proportional to avdd. with a 3.3v supply voltage, the full scale level is 1.0 volts r.m.s. any voltage greater than full scale may overload the adc and cause distortion. adc digital filter the adc filters perform true 24 bit signal processing to convert the raw multi-bit oversampled data from the adc to the correct sampling frequency to be output on the digital audio interface. the digital filter path is illustrated in figure 8. from adc digital hpf digital filter to digital a udio interface digital decimator a dchpd figure 8 adc digital filter the adc digital filters contain a digital high-pass filter, selectable via software control. the high-pass filter response is detailed in the digital filter characteristics section. when the high-pass filter is enabled the dc offset is continuously calculated and subtracted from the input signal. by setting hpor, the last calculated dc offset value is stored when the high-pass filter is disabled and will continue to be subtracted from the input signal. if the dc offset is changed, the stored and subtracted value will not change unless the high-pass filter is enabled. this feature can be used for calibration purposes. in addition the high-pass filter may be enabled separately on the left and right channels (see table 11). the output data format can be programmed by the user to accommodate stereo or monophonic recording on both inputs. the polarity of the output signal can also be changed under software control. the software control is shown in table 10. register address bit label default description 6:5 adcpol [1:0] 00 00 = polarity not inverted 01 = l polarity invert 10 = r polarity invert 11 = l and r polarity invert 4 hpor 0 store dc offset when high-pass filter disabled 1 = store offset 0 = clear offset r5 (05h) adc and dac control 0 adchpd 0 r27 (1bh) 5 hpflren 0 adchpd and hpflren together determine high-pass filter behaviour (see table 11) table 10 adc signal path control hpflren adchpd left channel right channel 0 0 hpf on hpf on 0 1 hpf off hpf off 1 0 hpf on hpf off 1 1 hpf off hpf on table 11 adc high pass filter modes
production data wm8988 w pd, rev 4.0, october 2008 21 digital adc volume control the output of the adcs can be digitally amplified or attenuated over a range from ?97db to +30db in 0.5db steps. the volume of each channel can be controlled separately. the gain for a given eight-bit code x is given by: 0.5 (x-195) db for 1 x 255; mute for x = 0 the lavu and ravu control bits control the loading of digital volume control data. when lavu or ravu are set to 0, the ladcvol or radcvol control data will be loaded into the respective control register, but will not actually change the digital gain setting. both left and right gain settings are updated when either lavu or ravu are set to 1. this makes it possible to update the gain of both channels simultaneously. register address bit label default description 7:0 ladcvol [7:0] 11000011 ( 0db ) left adc digital volume control 0000 0000 = digital mute 0000 0001 = -97db 0000 0010 = -96.5db ... 0.5db steps up to 1111 1111 = +30db r21 (15h) left adc digital volume 8 lavu 0 left adc volume update 0 = store ladcvol in intermediate latch (no gain change) 1 = update left and right channel gains (left = ladcvol, right = intermediate latch) 7:0 radcvol [7:0] 11000011 ( 0db ) right adc digital volume control 0000 0000 = digital mute 0000 0001 = -97db 0000 0010 = -96.5db ... 0.5db steps up to 1111 1111 = +30db r22 (16h) right adc digital volume 8 ravu 0 right adc volume update 0 = store radcvol in intermediate latch (no gain change) 1 = update left and right channel gains (left = intermediate latch, right = radcvol) table 12 adc digital volume control
wm8988 production data w pd, rev 4.0, october 2008 22 automatic level control (alc) the wm8988 has an automatic level control that aims to keep a constant recording volume irrespective of the input signal level. this is achieved by continuously adjusting the pga gain so that the signal level at the adc input remains constant. a digital peak detector monitors the adc output and changes the pga gain if necessary. note that when the alc function is enabled, the settings of registers 0 and 1 (linvol, livu, lizc, linmute, rinvol, rivu, rizc and rinmute) are ignored. hold time decay time attack time input signal signal after alc pga gain alc target level figure 9 alc operation the alc function is enabled using the alcsel control bits. when enabled, the recording volume can be programmed between ?6db and ?28.5db (relative to adc full scale) using the alcl register bits. an upper limit for the pga gain can be imposed by setting the maxgain control bits. hld, dcy and atk control the hold, decay and attack times, respectively: hold time is the time delay between the peak level detected being below target and the pga gain beginning to ramp up. it can be programmed in power-of-two (2 n ) steps, e.g. 2.67ms, 5.33ms, 10.67ms etc. up to 43.7s. alternatively, the hold time can also be set to zero. the hold time only applies to gain ramp-up, there is no delay before ramping the gain down when the signal level is above target. decay (gain ramp-up) time is the time that it takes for the pga gain to ramp up across 90% of its range (e.g. from ?15b up to 27.75db). the time it takes for the recording level to return to its target value therefore depends on both the decay time and on the gain adjustment required. if the gain adjustment is small, it will be shorter than the decay time. the decay time can be programmed in power-of-two (2 n ) steps, from 24ms, 48ms, 96ms, etc. to 24.58s. attack (gain ramp-down) time is the time that it takes for the pga gain to ramp down across 90% of its range (e.g. from 27.75db down to -15b gain). the time it takes for the recording level to return to its target value therefore depends on both the attack time and on the gain adjustment required. if the gain adjustment is small, it will be shorter than the attack time. the attack time can be programmed in power-of-two (2 n ) steps, from 6ms, 12ms, 24ms, etc. to 6.14s. when operating in stereo, the peak detector takes the maximum of left and right channel peak values, and any new gain setting is applied to both left and right pgas, so that the stereo image is preserved. however, the alc function can also be enabled on one channel only. in this case, only one pga is controlled by the alc mechanism, while the other channel runs independently with its pga gain set through the control register. when one adc channel is unused or used for dc measurement, the peak detector disregards that channel. the alc function can also operate when the two adc outputs are mixed to mono in the digital domain, but not if they are mixed to mono in the analogue domain, before entering the adcs.
production data wm8988 w pd, rev 4.0, october 2008 23 register address bit label default description 8:7 alcsel [1:0] 00 (off) alc function select 00 = alc off (pga gain set by register) 01 = right channel only 10 = left channel only 11 = stereo (pga registers unused) note: ensure that linvol and rinvol settings (reg. 0 and 1) are the same before entering this mode. 6:4 maxgain [2:0] 111 (+30db) set maximum gain of pga 111 : +30db 110 : +24db ?.(-6db steps) 001 : -6db 000 : -12db r17 (11h) alc control 1 3:0 alcl [3:0] 1011 (-12db) alc target ? sets signal level at adc input 0000 = -28.5db fs 0001 = -27.0db fs ? (1.5db steps) 1110 = -7.5db fs 1111 = -6db fs 7 alczc 0 (zero cross off) alc uses zero cross detection circuit. r18 (12h) alc control 2 3:0 hld [3:0] 0000 (0ms) alc hold time before gain is increased. 0000 = 0ms 0001 = 2.67ms 0010 = 5.33ms ? (time doubles with every step) 1111 = 43.7s 7:4 dcy [3:0] 0011 (192ms) alc decay (gain ramp-up) time 0000 = 24ms 0001 = 48ms 0010 = 96ms ? (time doubles with every step) 1010 or higher = 24.58s r19 (13h) alc control 3 3:0 atk [3:0] 0010 (24ms) alc attack (gain ramp-down) time 0000 = 6ms 0001 = 12ms 0010 = 24ms ? (time doubles with every step) 1010 or higher = 6.14s table 13 alc control peak limiter to prevent clipping when a large signal occurs just after a period of quiet, the alc circuit includes a limiter function. if the adc input signal exceeds 87.5% of full scale (?1.16db), the pga gain is ramped down at the maximum attack rate (as when atk = 0000), until the signal level falls below 87.5% of full scale. this function is automatically enabled whenever the alc is enabled. note: if atk = 0000, then the limiter makes no difference to the operation of the alc. it is designed to prevent clipping when long attack times are used.
wm8988 production data w pd, rev 4.0, october 2008 24 noise gate when the signal is very quiet and consists mainly of noise, the alc function may cause ?noise pumping?, i.e. loud hissing noise during silence periods. the wm8988 has a noise gate function that prevents noise pumping by comparing the signal level at the linput1/2 and/or rinput1/2 pins against a noise gate threshold, ngth. the noise gate cuts in when: ? signal level at adc [db] < ngth [db] + pga gain [db] + mic boost gain [db] this is equivalent to: ? signal level at input pin [db] < ngth [db] the adc output can then either be muted or alternatively, the pga gain can be held constant (preventing it from ramping up as it normally would when the signal is quiet). the table below summarises the noise gate control register. the ngth control bits set the noise gate threshold with respect to the adc full-scale range. the threshold is adjusted in 1.5db steps. levels at the extremes of the range may cause inappropriate operation, so care should be taken with set?up of the function. note that the noise gate only works in conjunction with the alc function, and always operates on the same channel(s) as the alc (left, right, both, or none). register address bit label default description 7:3 ngth [4:0] 00000 noise gate threshold 13 -76.5dbfs 13 -75dbfs ? 1.5 db steps 11110 -31.5dbfs 11111 -30dbfs 2:1 ngg [1:0] 00 noise gate type x0 = pga gain held constant 01 = mute adc output 11 = reserved (do not use this setting) r20 (14h) noise gate control 0 ngat 0 noise gate function enable 1 = enable 0 = disable table 14 noise gate control note: the performance of the adc may degrade at high input signal levels if the monitor bypass mux is selected with mic boost and alc enabled.
production data wm8988 w pd, rev 4.0, october 2008 25 3d stereo enhancement the wm8988 has a digital 3d enhancement option to artificially increase the separation between the left and right channels. this effect can be used for recording or playback, but not for both simultaneously. selection of 3d for record or playback is controlled by register bit mode3d. important: switching the 3d filter from record to playback or from playback to record may only be done when adc and dac are disabled. the wm8988 control interface will only allow mode3d to be changed when adc and dac are disabled (i.e. bits adcl, adcr, dacl and dacr in reg. 26 / 1ah are all zero). the 3d enhancement function is activated by the 3den bit, and has two programmable parameters. the 3ddepth setting controls the degree of stereo expansion. additionally, one of four filter characteristics can be selected for the 3d processing, using the 3dvc and 3dlc control bits. register address bit label default description 7 mode3d 0 playback/record 3d select 0 = 3d selected for record 1 = 3d selected for playback 6 3duc 0 upper cut-off frequency 0 = high (2.2khz at 48khz sampling) 1 = low (1.5khz at 48khz sampling) 5 3dlc 0 lower cut-off frequency 0 = low (200hz at 48khz sampling) 1 = high (500hz at 48khz sampling) 4:1 3ddepth [3:0] 0000 stereo depth 0000: 0% (minimum 3d effect) 0001: 6.67% .... 1110: 93.3% 1111: 100% (maximum 3d effect) r16 (10h) 3d enhance 0 3den 0 3d function enable 1: enabled 0: disabled table 15 3d stereo enhancement function when 3d enhancement is enabled (and/or the graphic equaliser for playback) it may be necessary to attenuate the signal by 6db to avoid limiting. this is a user selectable function, enabled by setting adcdiv2 for the record path and dacdiv2 for the playback path. register address bit label default description 8 adcdiv2 0 adc 6db attenuate enable 0 = disabled (0db) 1 = -6db enabled r5 (05h) adc and dac control 7 dacdiv2 0 dac 6db attenuate enable 0 = disabled (0db) 1 = -6db enabled table 16 adc and dac 6db attenuation select
wm8988 production data w pd, rev 4.0, october 2008 26 output signal path the wm8988 output signal paths consist of digital filters, dacs, analogue mixers and output drivers. the digital filters and dacs are enabled when the wm8988 is in ?playback only? or ?record and playback? mode. the mixers and output drivers can be separately enabled by individual control bits (see analogue outputs). thus it is possible to utilise the analogue mixing and amplification provided by the wm8988, irrespective of whether the dacs are running or not. the wm8988 receives digital input data on the dacdat pin. the digital filter block processes the data to provide the following functions: ? digital volume control ? graphic equaliser and dynamic bass boost ? sigma-delta modulation two high performance sigma-delta audio dacs convert the digital data into two analogue signals (left and right). these can then be mixed with analogue signals from the linput1/2 and rinput1/2 pins, and the mix is fed to the output drivers, lout1/rout1 and lout2/rout2. ? lout1/rout1: can drive a 16 ? or 32 ? stereo headphone or stereo line output. ? lout2/rout2: can drive a 16 ? or 32 ? stereo headphone or stereo line output digital dac volume control the signal volume from each dac can be controlled digitally, in the same way as the adc volume (see digital adc volume control). the gain and attenuation range is ?127db to 0db in 0.5db steps. the level of attenuation for an eight-bit code x is given by: 0.5 (x-255) db for 1 x 255; mute for x = 0 the ldvu and rdvu control bits control the loading of digital volume control data. when ldvu or rdvu are set to 0, the ldacvol or rdacvol control data is loaded into an intermediate register, but the actual gain does not change. both left and right gain settings are updated simultaneously when either ldvu or rdvu are set to 1. register address bit label default description 8 ldvu 0 left dac volume update 0 = store ldacvol in intermediate latch (no gain change) 1 = update left and right channel gains (left = ldacvol, right = intermediate latch) r10 (0ah) left channel digital volume 7:0 ldacvol [7:0] 11111111 ( 0db ) left dac digital volume control 0000 0000 = digital mute 0000 0001 = -127db 0000 0010 = -126.5db ... 0.5db steps up to 1111 1111 = 0db 8 rdvu 0 right dac volume update 0 = store rdacvol in intermediate latch (no gain change) 1 = update left and right channel gains (left = intermediate latch, right = rdacvol) r11 (0bh) right channel digital volume 7:0 rdacvol [7:0] 11111111 ( 0db ) right dac digital volume control similar to ldacvol table 17 digital volume control
production data wm8988 w pd, rev 4.0, october 2008 27 graphic equaliser the wm8988 has a digital graphic equaliser and adaptive bass boost function. this function operates on digital audio data before it is passed to the audio dacs. bass enhancement can take two different forms: ? linear bass control: bass signals are amplified or attenuated by a user programmable gain. this is independent of signal volume, and very high bass gains on loud signals may lead to signal clipping. ? adaptive bass boost: the bass volume is amplified by a variable gain. when the bass volume is low, it is boosted more than when the bass volume is high. this method is recommended because it prevents clipping, and usually sounds more pleasant to the human ear. treble control applies a user programmable gain, without any adaptive boost function. bass and treble control are completely independent with separately programmable gains and filter characteristics. register address bit label default description 7 bb 0 bass boost 0 = linear bass control 1 = adaptive bass boost 6 bc 0 bass filter characteristic 0 = low cutoff (130hz at 48khz sampling) 1 = high cutoff (200hz at 48khz sampling) bass intensity code bb=0 bb=1 0000 +9db 15 (max) 0001 +9db 14 0010 +7.5db 13 0011 +6db 12 0100 +4.5db 11 0101 +3db 10 0110 +1.5db 9 0111 0db 8 1000 -1.5db 7 1001 -3db 6 1010 -4.5db 5 1011 -6db 4 1100 -6db 3 1101 -6db 2 1110 -6db 1 r12 (0ch) bass control 3:0 bass [3:0] 1111 (disabled) 1111 bypass (off) 6 tc 0 treble filter characteristic 0 = high cutoff (8khz at 48khz sampling) 1 = low cutoff (4khz at 48khz sampling) r13 (0dh) treble control 3:0 trbl [3:0] 1111 (disabled) treble intensity 0000 or 0001 = +9db 0010 = +7.5db ? (1.5db steps) 1011 to 1110 = -6db 1111 = disable table 18 graphic equaliser
wm8988 production data w pd, rev 4.0, october 2008 28 digital to analogue converter (dac) after passing through the graphic equaliser filters, digital ?de-emphasis? can be applied to the audio data if necessary (e.g. when the data comes from a cd with pre-emphasis used in the recording). de-emphasis filtering is available for sample rates of 48khz, 44.1khz and 32khz. the wm8988 also has a soft mute function, which gradually attenuates the volume of the digital signal to zero. when removed, the gain will return to the original setting. this function is enabled by default. to play back an audio signal, it must first be disabled by setting the dacmu bit to zero. register address bit label default description 2:1 deemp [1:0] 00 de-emphasis control 11 = 48khz sample rate 10 = 44.1khz sample rate 01 = 32khz sample rate 00 = no de-emphasis r5 (05h) adc and dac control 3 dacmu 1 digital soft mute 1 = mute 0 = no mute (signal active) table 19 dac control the digital audio data is converted to oversampled bit streams in the on-chip, true 24-bit digital interpolation filters. the bitstream data enters two multi-bit, sigma-delta dacs, which convert them to high quality analogue audio signals. the multi-bit dac architecture reduces high frequency noise and sensitivity to clock jitter. it also uses a dynamic element matching technique for high linearity and low distortion. in normal operation, the left and right channel digital audio data is converted to analogue in two separate dacs. however, it is also possible to disable one channel, so that the same signal (left or right) appears on both analogue output channels. additionally, there is a mono-mix mode where the two audio channels are mixed together digitally and then converted to analogue using only one dac, while the other dac is switched off. the mono-mix signal can be selected to appear on both analogue output channels. the dac output defaults to non-inverted. setting dacinv will invert the dac output phase on both left and right channels. register address bit label default description 5:4 dmonomix [1:0] 00 dac mono mix 00: stereo 01: mono ((l+r)/2) into dacl, ?0? into dacr 10: mono ((l+r)/2) into dacr, ?0? into dacl 11: mono ((l+r)/2) into dacl and dacr r23 (17h) additional control (1) 1 dacinv 0 dac phase invert 0 : non-inverted 1 : inverted table 20 dac mono mix and phase invert select
production data wm8988 w pd, rev 4.0, october 2008 29 output mixers the wm8988 provides the option to mix the dac output signal with analogue line-in signals from the linput1/2, rinput1/2 pins or a mono differential input (linput1 ? rinput1) or (linput2 ? rinput2), selected by ds (see table 6) . the level of the mixed-in signals can be controlled with pgas (programmable gain amplifiers). the mono mixer is designed to allow a number of signal combinations to be mixed, including the possibility of mixing both the right and left channels together to produce a mono output. to prevent overloading of the mixer when full-scale dac left and right signals are input, the mixer inputs from the dac outputs each have a fixed gain of -6db. the bypass path inputs to the mono mixer have variable gain as determined by r38/r39 bits [6:4]. register address bit label default description r34 (22h) left mixer (1) 2:0 lmixsel 000 left input selection for output mix 000 = linput1 001 = linput2 010 = reserved 011 = left adc input (after pga / micboost) 100 = differential input r36 (24h) right mixer (1) 2:0 rmixsel 000 right input selection for output mix 000 = rinput1 001 = rinput2 010 = reserved 011 = right adc input (after pga / micboost) 100 = differential input table 21 output mixer signal selection register address bit label default description 8 ld2lo 0 left dac to left mixer 0 = disable (mute) 1 = enable path 7 li2lo 0 lmixsel signal to left mixer 0 = disable (mute) 1 = enable path r34 (22h) left mixer control (1) 6:4 li2lovol [2:0] 101 (-9db) lmixsel signal to left mixer volume 000 = +6db ? (3db steps) 111 = -15db 8 rd2lo 0 right dac to left mixer 0 = disable (mute) 1 = enable path 7 ri2lo 0 rmixsel signal to left mixer 0 = disable (mute) 1 = enable path r35 (23h) left mixer control (2) 6:4 ri2lovol [2:0] 101 (-9db) rmixsel signal to left mixer volume 000 = +6db ? (3db steps) 111 = -15db table 22 left output mixer control
wm8988 production data w pd, rev 4.0, october 2008 30 register address bit label default description 8 ld2ro 0 left dac to right mixer 0 = disable (mute) 1 = enable path 7 li2ro 0 lmixsel signal to right mixer 0 = disable (mute) 1 = enable path r36 (24h) right mixer control (1) 6:4 li2rovol [2:0] 101 (-9db) lmixsel signal to right mixer volume 000 = +6db ? (3db steps) 111 = -15db 8 rd2ro 0 right dac to right mixer 0 = disable (mute) 1 = enable path 7 ri2ro 0 rmixsel signal to right mixer 0 = disable (mute) 1 = enable path r37 (25h) right mixer control (2) 6:4 ri2rovol [2:0] 101 (-9db) rmixsel signal to right mixer volume 000 = +6db ? (3db steps) 111 = -15db table 23 right output mixer control
production data wm8988 w pd, rev 4.0, october 2008 31 analogue outputs lout1/rout1 outputs the lout1 and rout1 pins can drive a 16 ? or 32 ? headphone or a line output (see headphone output and line output sections, respectively). the signal volume on lout1 and rout1 can be independently adjusted under software control by writing to lout1vol and rout1vol, respectively. note that gains over 0db may cause clipping if the signal is large. any gain setting below 0101111 (minimum) mutes the output driver. the corresponding output pin remains at the same dc level (the reference voltage on the vref pin), so that no click noise is produced when muting or un-muting. a zero cross detect on the analogue output may also be enabled when changing the gain setting to minimize audible cli cks and zipper noise as the gain updates. if zero cross is enabled a timeout is also available to update the gain if a zero cross does not occur. this function may be enabled by setting toen in register r23 (17h). register address bit label default description 8 lo1vu 0 left volume update 0 = store lout1vol in intermediate latch (no gain change) 1 = update left and right channel gains (left = lout1vol, right = intermediate latch) 7 lo1zc 0 left zero cross enable 1 = change gain on zero cross only 0 = change gain immediately r2 (02h) lout1 volume 6:0 lout1vol [6:0] 1111001 (0db) lout1 volume 1111111 = +6db ? (80 steps) 0110000 = -67db 0111111 to 0000000 = analogue mute 8 ro1vu 0 right volume update 0 = store rout1vol in intermediate latch (no gain change) 1 = update left and right channel gains (left = intermediate latch, right = rout1vol) 7 ro1zc 0 right zero cross enable 1 = change gain on zero cross only 0 = change gain immediately r3 (03h) rout1 volume 6:0 rout1vol [6:0] 1111001 rout1 volume 1111111 = +6db ? (80 steps) 0110000 = -67db 0111111 to 0000000 = analogue mute table 24 lout1/rout1 volume control lout1/rout1 common ground feedback (hpcom) the lout1/rout1 outputs also have the option of incorporating common ground feedback from the output signal ground, via a connection to the hpcom input. this common ground feedback signal should be ac-coupled via a 4.7uf capacitor for the headphone loads. ac coupling of these outputs if they are used as line level outputs requires similar 1 to 4.7uf ac coupling capacitors depending upon line load resistance.
wm8988 production data w pd, rev 4.0, october 2008 32 register address bit label default description r24 (18h) hpcom control 7 hpcomen 0 enables common mode feedback on lout1 and rout1 0: disable common mode feedback 1: enable common mode feedback table 25 hpcom control lout2/rout2 outputs the lout2 and rout2 output pins are essentially similar to lout1 and rout1, but they are independently controlled . register address bit label default description 6:0 lout2vol [6:0] 1111001 (0db) lout2 volume 1111111 = +6db ? (80 steps) 0110000 = -67db 0111111 to 0000000 = analogue mute 7 lo2zc 0 left zero cross enable 1 = change gain on zero cross only 0 = change gain immediately r40 (28h) lout2 volume 8 lo2vu 0 same as lo1vu 6:0 rout2vol [6:0] 1111001 (0db) rout2 volume 1111111 = +6db ? (80 steps) 0110000 = -67db 0111111 to 0000000 = analogue mute 7 ro2zc 0 right zero cross enable 1 = change gain on zero cross only 0 = change gain immediately r41 (29h) rout2 volume 8 ro2vu 0 same as ro1vu r24 (18h) additional control (2) 4 rout2inv 0 rout2 invert 0 = no inversion (0 phase shift) 1 = signal inverted (180 phase shift) table 26 lout2/rout2 volume control lout2/rout2 common ground feedback (lcom) the lout2/rout2 outputs also have the option of incorporating common ground feedback from the output signal ground, via a connection to the lcom input. this common ground feedback signal should be ac-coupled via a 4.7uf capacitor for headphone loads. ac coupling of these outputs if they are used as line level outputs requires similar 1 to 4.7uf ac coupling capacitors depending upon line load resistance. register address bit label default description r24 (18h) lcom control 8 lcomen 0 enables common mode feedback on lout2 and rout2 0: disable common mode feedback 1: enable common mode feedback table 27 lcom control
production data wm8988 w pd, rev 4.0, october 2008 33 enabling the outputs each analogue output of the wm8988 can be separately enabled or disabled. the analogue mixer associated with each output is powered on or off along with the output pin. all outputs are disabled by default. to save power, unused outputs should remain disabled. outputs can be enabled at any time, except when vref is disabled (vr=0), as this may cause pop noise (see ?power management? and ?applications information? sections) register address bit label default description 6 lout1 0 lout1 enable 5 rout1 0 rout1 enable 4 lout2 0 lout2 enable r26 (1ah) power management (2) 3 rout2 0 rout2 enable note: all ?enable? bits are 1 = enabled, 0 = disabled table 28 analogue output control whenever an analogue output is disabled, it remains connected to vref (pin 20) through a resistor. this helps to prevent pop noise when the output is re-enabled. the resistance between vref and each output can be controlled using the vroi bit in register 27. the default is low (1.5k ? ), so that any capacitors on the outputs can charge up quickly at start-up. if a high impedance is desired for disabled outputs, vroi can then be set to 1, increasing the resistance to about 40k ? . register address bit label default description r27 (1bh) additional (1) 6 vroi 0 vref to analogue output resistance 0: 1.5 k ? 1: 40 k ? table 29 disabled outputs to vref resistance thermal shutdown the headphone outputs can drive very large currents. to protect the wm8988 from overheating a thermal shutdown circuit is included. if the device temperature reaches approximately 150 0 c and the thermal shutdown circuit is enabled (tsden = 1 ) then the headphone amplifiers (outputs out1l/r and out2l/r) will be disabled. register address bit label default description r23 (17h) additional control (1) 8 tsden 0 thermal shutdown enable 0 : thermal shutdown disabled 1 : thermal shutdown enabled table 30 thermal shutdown
wm8988 production data w pd, rev 4.0, october 2008 34 digital audio interface the digital audio interface is used for inputting dac data into the wm8988 and outputting adc data from it. it uses four pins: ? adcdat: adc data output ? dacdat: dac data input ? lrc: dac and adc data alignment clock ? bclk: bit clock, for synchronisation the clock signals bclk and lrc can be an output when the wm8988 operates as a master, or an input when it is a slave (see master and slave mode operation, below). four different audio data formats are supported: ? left justified ? i 2 s ? dsp mode all four of these modes are msb first. they are described in audio data formats, below. refer to the electrical characteristic section for timing information. master and slave mode operation the wm8988 can be configured as either a master or slave mode device. as a master device the wm8988 generates bclk, adclrc and daclrc and thus controls sequencing of the data transfer on adcdat and dacdat. in slave mode, the wm8988 responds with data to clocks it receives over the digital audio interface. the mode can be selected by writing to the ms bit (see table 23). master and slave modes are illustrated below. figure 10 master mode figure 11 slave mode audio data formats in left justified mode, the msb is available on the first rising edge of bclk following a lrclk transition. the other bits up to the lsb are then transmitted in order. depending on word length, bclk frequency and sample rate, there may be unused bclk cycles before each lrclk transition. figure 12 left justified audio interface (assuming n-bit word length) in i 2 s mode, the msb is available on the second rising edge of bclk following a lrclk transition. the other bits up to the lsb are then transmitted in order. depending on word length, bclk frequency and sample rate, there may be unused bclk cycles between the lsb of one sample and the msb of the next.
production data wm8988 w pd, rev 4.0, october 2008 35 figure 13 i 2 s justified audio interface (assuming n-bit word length) in dsp/pcm mode, the left channel msb is available on either the 1 st (mode b) or 2 nd (mode a) rising edge of bclk (selectable by lrp) following a rising edge of lrc. right channel data immediately follows left channel data. depending on word length, bclk frequency and sample rate, there may be unused bclk cycles between the lsb of the right channel data and the next sample. in device master mode, the lrc output will resemble the frame pulse shown in figure 14 and figure 15. in device slave mode, figure 16 and figure 17, it is possible to use any length of frame pulse less than 1/fs, providing the falling edge of the frame pulse occurs greater than one bclk period before the rising edge of the next frame pulse. figure 14 dsp/pcm mode audio interface (mode a, lrp=0, master) figure 15 dsp/pcm mode audio interface (mode b, lrp=1, master)
wm8988 production data w pd, rev 4.0, october 2008 36 figure 16 dsp/pcm mode audio interface (mode a, lrp=0, slave) figure 17 dsp/pcm mode audio interface (mode b, lrp=0, slave)
production data wm8988 w pd, rev 4.0, october 2008 37 audio interface control the register bits controlling audio format, word length and master / slave mode are summarised in table 31. ms selects audio interface operation in master or slave mode. in master mode bclk and lrc are outputs. the frequency of lrc is set by the sample rate control bits sr[4:0] and usb. in slave mode bclk and lrc are inputs. register address bit label default description 7 bclkinv 0 bclk invert bit (for master and slave modes) 0 = bclk not inverted 1 = bclk inverted 6 ms 0 master / slave mode control 1 = enable master mode 0 = enable slave mode 5 lrswap 0 left/right channel swap 1 = swap left and right dac data in audio interface 0 = output left and right data as normal right, left and i2s modes ? lrclk polarity 1 = invert lrclk polarity 0 = normal lrclk polarity 4 lrp 0 dsp mode ? mode a/b select 1 = msb is available on 1 st bclk rising edge after lrc rising edge (mode b) 0 = msb is available on 2 nd bclk rising edge after lrc rising edge (mode a) 3:2 wl[1:0] 10 audio data word length 11 = 32 bits (see note) 10 = 24 bits 01 = 20 bits 00 = 16 bits r7 (07h) digital audio interface format 1:0 format[1:0] 10 audio data format select 11 = dsp mode 10 = i 2 s format 01 = left justified 00 = reserved (do not use this setting) table 31 audio data format control audio interface output tristate register bit tri, register 24(18h) bit[3] can be used to tristate the adcdat pin and switch adclrc, daclrc and bclk to inputs. in slave mode (master=0) lrc and bclk are by default configured as inputs and only adcdat will be tri-stated, (see table 32). register address bit label default description r24(18h) additional control (2) 3 tri 0 tristates adcdat and switches adclrc, daclrc and bclk to inputs. 0 = adcdat is an output, lrc and bclk are inputs (slave mode) or outputs (master mode) 1 = adcdat is tristated, lrc and bclk are inputs table 32 tri-stating the audio interface
wm8988 production data w pd, rev 4.0, october 2008 38 master mode lrc enable in master mode the lrclk (lrc) is enabled by default only when the dac is enabled. if adc only operation in master mode is required register bit lrcm must be set in oder to generate an lrclk. for dac only operation lrcm may be set to ?0?. register address bit label default description r24(18h) additional control (2) 2 lrcm 0 selects disable mode for lrc 0 = lrc disabled when dac (left and right) disabled. 1 = lrc disabled only when adc (left and right) and dac (left and right) are disabled. table 33 lrc enable bit clock mode the default master mode bit clock generator produces a bit clock frequency based on the sample rate and input mclk frequency as shown in table 36. when enabled by setting the appropriate bcm[1:0] bits, the bit clock mode (bcm) function overrides the default master mode bit clock generator to produce the bit clock frequency shown in the table below: register address bit label default description r8 (08h) clocking and sample rate control 8:7 bcm[1:0] 00 bclk frequency 00 = bcm function disabled 01 = mclk/4 10 = mclk/8 11 = mclk/16 table 34 master mode bclk frequency control the bcm mode bit clock generator produces 16 or 24 bit clock cycles per sample. the number of bit clock cycles per sample in this mode is determined by the word length bits (wl[1:0]) in the digital audio interface format register (r7). when these bits are set to 00, there will be 16 bit clock cycles per sample. when these bits are set to 01, 10 or 11, there will be 24 bit clock cycles per sample. please refer to figure 18 . in order to use bcm either the adc must be enabled or, if the adc is disabled, the lrcm bit must be set and the dac enabled. when the bcm function is enabled, the following restrictions apply: 1. the bit clock invert (bclkinv) function is not available. 2. dsp late digital audio interface mode is not available and must not be enabled. figure 18 bit clock mode note: the shaded bit clock cycles are present only when 24-bit mode is selected. please refer to the ?bit clock mode? description for details.
production data wm8988 w pd, rev 4.0, october 2008 39 clocking and sample rates the wm8988 supports a wide range of master clock frequencies on the mclk pin, and can generate many commonly used audio sample rates directly from the master clock. the adc and dac must always run at the same sample rate. there are two clocking modes: ? ?normal? mode supports master clocks of 128f s , 192f s , 256f s , 384f s , and their multiples (note: f s refers to the adc or dac sample rate, whichever is faster) ? usb mode supports 12mhz or 24mhz master clocks. this mode is intended for use in systems with a usb interface, and eliminates the need for an external pll to generate another clock frequency for the audio codec. register address bit label default description 6 clkdiv2 0 master clock divide by 2 1 = mclk is divided by 2 0 = mclk is not divided 5:1 sr [4:0] 00000 sample rate control r8 (08h) clocking and sample rate control 0 usb 0 clocking mode select 1 = usb mode 0 = ?normal? mode table 35 clocking and sample rate control the clocking of the wm8988 is controlled using the clkdiv2, usb, and sr control bits. setting the clkdiv2 bit divides mclk by two internally. the usb bit selects between ?normal? and usb mode. each value of sr[4:0] selects one combination of mclk division ratios and hence one combination of sample rates (see next page). since all sample rates are generated by dividing mclk, their accuracy depends on the accuracy of mclk. if mclk changes, the sample rates change proportionately. note that some sample rates (e.g. 44.1khz in usb mode) are approximated, i.e. they differ from their target value by a very small amount. this is not audible, as the maximum deviation is only 0.27% (8.0214khz instead of 8khz in usb mode). by comparison, a half-tone step corresponds to a 5.9% change in pitch. the sr[4:0] bits must be set to configure the appropriate adc and dac sample rates in both master and slave mode.
wm8988 production data w pd, rev 4.0, october 2008 40 mclk clkdiv2=0 mclk clkdiv2=1 adc sample rate (adclrc) dac sample rate (daclrc) usb sr [4:0] filter type bclk (ms=1) ?normal? clock mode (?*? indicates backward compatibility with wm8731) 8 khz (mclk/1536) 8 khz (mclk/1536) 0 00110 * 1 mclk/4 12 khz (mclk/1024) 12 khz (mclk/1024) 0 01000 1 mclk/4 16 khz (mclk/768) 16 khz (mclk/768) 0 01010 1 mclk/4 24 khz (mclk/512) 24 khz (mclk/512) 0 11100 1 mclk/4 32 khz (mclk/384) 32 khz (mclk/384) 0 01100 * 1 mclk/4 48 khz (mclk/256) 48 khz (mclk/256) 0 00000 * 1 mclk/4 12.288 mhz 24.576 mhz 96 khz (mclk/128) 96 khz (mclk/128) 0 01110 * 3 mclk/2 8.0182 khz (mclk/1408) 8.0182 khz (mclk/1408) 0 10110 * 1 mclk/4 11.025 khz (mclk/1024) 11.025 khz (mclk/1024) 0 11000 1 mclk/4 22.05 khz (mclk/512) 22.05 khz (mclk/512) 0 11010 1 mclk/4 44.1 khz (mclk/256) 44.1 khz (mclk/256) 0 10000 * 1 mclk/4 11.2896mhz 22.5792mhz 88.2 khz (mclk/128) 88.2 khz (mclk/128) 0 11110 * 3 mclk/2 8 khz (mclk/2304) 8 khz (mclk/2304) 0 00111 * 1 mclk/6 12 khz (mclk/1536) 12 khz (mclk/1536) 0 01001 1 mclk/6 16khz (mclk/1152) 16 khz (mclk/1152) 0 01011 1 mclk/6 24khz (mclk/768) 24 khz (mclk/768) 0 11101 1 mclk/6 32 khz (mclk/576) 32 khz (mclk/576) 0 01101 * 1 mclk/6 48 khz (mclk/384) 48 khz (mclk/384) 0 00001 * 1 mclk/6 18.432mhz 36.864mhz 96 khz (mclk/192) 96 khz (mclk/192) 0 01111 * 3 mclk/3 8.0182 khz (mclk/2112) 8.0182 khz (mclk/2112) 0 10111 * 1 mclk/6 11.025 khz (mclk/1536) 11.025 khz (mclk/1536) 0 11001 1 mclk/6 22.05 khz (mclk/768) 22.05 khz (mclk/768) 0 11011 1 mclk/6 44.1 khz (mclk/384) 44.1 khz (mclk/384) 0 10001 * 1 mclk/6 16.9344mhz 33.8688mhz 88.2 khz (mclk/192) 88.2 khz (mclk/192) 0 11111 * 3 mclk/3 usb mode (?*? indicates backward compatibility with wm8731) 8 khz (mclk/1500) 8 khz (mclk/1500) 1 00110 * 0 mclk 8.0214 khz (mclk/1496) 8.0214khz (mclk/1496) 1 10111 * 1 mclk 11.0259 khz (mclk/1088) 11.0259khz (mclk/1088) 1 11001 1 mclk 12 khz (mclk/1000) 12 khz (mclk/1000) 1 01000 0 mclk 16khz (mclk/750) 16khz (mclk/750) 1 01010 0 mclk 22.0588khz (mclk/544) 22.0588khz (mclk/544) 1 11011 1 mclk 24khz (mclk/500) 24khz (mclk/500) 1 11100 0 mclk 32 khz (mclk/375) 32 khz (mclk/375) 1 01100 * 0 mclk 44.118 khz (mclk/272) 44.118 khz (mclk/272) 1 10001 * 1 mclk 48 khz (mclk/250) 48 khz (mclk/250) 1 00000 * 0 mclk 88.235khz (mclk/136) 88.235khz (mclk/136) 1 11111 * 3 mclk 12.000mhz 24.000mhz 96 khz (mclk/125) 96 khz (mclk/125) 1 01110 * 2 mclk table 36 master clock and sample rates
production data wm8988 w pd, rev 4.0, october 2008 41 control interface selection of control mode the wm8988 is controlled by writing to registers through a serial control interface. a control word consists of 16 bits. the first 7 bits (b15 to b9) are address bits that select which control register is accessed. the remaining 9 bits (b8 to b0) are data bits, corresponding to the 9 bits in each control register. the control interface can operate as either a 3-wire or 2-wire mpu interface. the mode pin selects the interface format. mode interface format low 2 wire high 3 wire table 37 control interface mode selection 3-wire serial control mode in 3-wire mode, every rising edge of sclk clocks in one data bit from the sdin pin. a rising edge on csb latches in a complete control word consisting of the last 16 bits. b15 b14 b13 b12 b11 b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0 sdin sclk csb control register address control register data bits latch figure 19 3-wire serial control interface 2-wire serial control mode the wm8988 supports software control via a 2-wire serial bus. many devices can be controlled by the same bus, and each device has a unique 7-bit address (this is not the same as the 7-bit address of each register in the wm8988). the wm8988 operates as a slave device only. the controller indicates the start of data transfer with a high to low transition on sdin while sclk remains high. this indicates that a device address and data will follow. all devices on the 2-wire bus respond to the start condition and shift in the next eight bits on sdin (7-bit address + read/write bit, msb first). if the device address received matches the address of the wm8988 and the r/w bit is ?0?, indicating a write, then the wm8988 responds by pulling sdin low on the next clock pulse (ack). if the address is not recognised or the r/w bit is ?1?, the wm8988 returns to the idle condition and wait for a new start condition and valid address. once the wm8988 has acknowledged a correct address, the controller sends the first byte of control data (b15 to b8, i.e. the wm8988 register address plus the first bit of register data). the wm8988 then acknowledges the first data byte by pulling sdin low for one clock pulse. the controller then sends the second byte of control data (b7 to b0, i.e. the remaining 8 bits of register data), and the wm8988 acknowledges again by pulling sdin low. the transfer of data is complete when there is a low to high transition on sdin while sclk is high. after receiving a complete address and data sequence the wm8988 returns to the idle state and waits for another start condition. if a start or stop condition is detected out of sequence at any point during data transfer (i.e. sdin changes while sclk is high), the device jumps to the idle condition. sdin sclk register address and 1st register data bit device address (7 bits) rd / wr bit ack (low) control byte 1 (bits 15 to 8) control byte 2 (bits 7 to 0) remaining 8 bits of register data stop start ack (low) ack (low) figure 20 2-wire serial control interface
wm8988 production data w pd, rev 4.0, october 2008 42 the wm8988 has two possible device addresses, which can be selected using the csb pin. csb state device address low 0011010 (0 x 34h) high 0011011 (0 x 36h) table 38 2-wire mpu interface address selection power supplies the wm8988 can use up to four separate power supplies: ? avdd / agnd: analogue supply, powers all analogue functions except the headphone drivers. avdd can range from 1.8v to 3.6v and has the most significant impact on overall power consumption (except for power consumed in the headphone). a large avdd slightly improves audio quality. ? hpvdd / hpgnd: headphone supply, powers the headphone drivers. hpvdd is normally tied to avdd, but it requires separate layout and decoupling capacitors to curb harmonic distortion. if hpvdd is lower than avdd, the output signal may be clipped. ? dcvdd: digital core supply, powers all digital functions except the audio and control interfaces. dcvdd can range from 1.42v to 3.6v, and has no effect on audio quality. the return path for dcvdd is dgnd, which is shared with dbvdd. ? dbvdd: digital buffer supply, powers the audio and control interface buffers. this makes it possible to run the digital core at very low voltages, saving power, while interfacing to other digital devices using a higher voltage. dbvdd draws much less power than dcvdd, and has no effect on audio quality. dbvdd can range from 1.8v to 3.6v. the return path for dbvdd is dgnd, which is shared with dcvdd. it is possible to use the same supply voltage on all four. however, digital and analogue supplies should be routed and decoupled separately to keep digital switching noise out of the analogue signal paths. power management the wm8988 has two control registers that allow users to select which functions are active. for minimum power consumption, unused functions should be disabled. to avoid any pop or click noise, it is important to enable or disable functions in the correct order (see applications information). vmidsel is the enable for the vmid reference, which defaults to disabled and can be enabled as a 50k ? potential divider or, for low power maintenance of vref when all other blocks are disabled, as a 500k ? potential divider.
production data wm8988 w pd, rev 4.0, october 2008 43 register address bit label default description 8:7 vmidsel 00 vmid divider enable and select 00 ? vmid disabled (for off mode) 01 ? 50k ? divider enabled (for playback/record) 10 ? 500k ? divider enabled (for low-power standby) 11 ? 5k ? divider enabled (for fast start-up) 6 vref 0 vref (necessary for all other functions) 0 = power down 1 = power up 5 ainl 0 analogue in pga left 0 = power down 1 = power up 4 ainr 0 analogue in pga right 0 = power down 1 = power up 3 adcl 0 adc left 0 = power down 1 = power up r25 (19h) power management (1) 2 adcr 0 adc right 0 = power down 1 = power up 8 dacl 0 dac left 0 = power down 1 = power up 7 dacr 0 dac right 0 = power down 1 = power up 6 lout1 0 lout1 output buffer* 0 = power down 1 = power up 5 rout1 0 rout1 output buffer* 0 = power down 1 = power up 4 lout2 0 lout2 output buffer* 0 = power down 1 = power up r26 (1ah) power management (2) 3 rout2 0 rout2 output buffer* 0 = power down 1 = power up * the left mixer is enabled when lout1=1 or lout2=1. the right mixer is enabled when rout1=1 or rout2=1. table 39 power management
wm8988 production data w pd, rev 4.0, october 2008 44 stopping the master clock in order to minimise power consumed in the digital core of the wm8988, the master clock may be stopped in standby and off modes. if this cannot be done externally at the clock source, the digenb bit (r25, bit 0) can be set to stop the mclk signal from propagating into the device core. in standby mode, setting digenb will typically provide an additional power saving on dcvdd of 20ua. however, since setting digenb has no effect on the power consumption of other system components external to the wm8988, it is preferable to disable the master clock at its source wherever possible. register address bit label default description r25 (19h) additional control (1) 0 digenb 0 master clock disable 0: master clock enabled 1: master clock disabled table 40 adc and dac oversampling rate selection note: before digenb can be set, the control bits adcl, adcr, dacl and dacr must be set to zero and a waiting time of 1ms must be observed. any failure to follow this procedure may prevent dacs and adcs from re-starting correctly. saving power by reducing bias currents the design of the dac allows user trade-off between power consumption and performance, using the dacmixbias bit. the default setting (dacmixbias=0) delivers the best audio performance. setting dacmixbias=1 reduces avdd current consumption, at the cost of marginally reduced performance (see ?electrical characteristics? for details). register address bit label default description r67 (43h) 3 dacmix bias 0 dac biasing 0 = high bias current (results in higher performance and power consumption) 1 = low bias current (results in lower performance and power consumption) table 41 dac biasing saving power by reducing oversampling rate the default mode of operation of the adc and dac digital filters is in 128x oversampling mode. under the control of adcosr and dacosr the oversampling rate may be halved. this will result in a slight decrease in noise performance but will also reduce the power consumption of the device. in usb mode adcosr must be set to 0, i.e. 128x oversampling. register address bit label default description 1 adcosr 0 adc oversample rate select 1 = 64x (lowest power) 0 = 128x (best snr) r24 (18h) additional control (2) 0 dacosr 0 dac oversample rate select 1 = 64x (lowest power) 0 = 128x (best snr) table 42 adc and dac oversampling rate selection adcosr set to ?1?, 64x oversample mode, is not supported in usb mode (usb=1).
production data wm8988 w pd, rev 4.0, october 2008 45 saving power at higher supply voltages the analogue supplies to the wm8988 can run from 1.8v to 3.6v. by default, all analogue circuitry on the device is optimized to run at 3.3v. this set-up is also good for all other supply voltages down to 1.8v. at lower voltages, performance can be improved by increasing the bias current. if low power operation is preferred the bias current can be left at the default setting. this is controlled as shown below. register address bit label default description r23 (17h) additional control(1) 7:6 vsel [1:0] 11 analogue bias optimization 00: highest bias current, optimized for avdd=1.8v 01: bias current optimized for avdd=2.5v 1x: lowest bias current, optimized for avdd=3.3v
wm8988 production data w pd, rev 4.0, october 2008 46 register map register address (bit 15 ? 9) remarks bit[8] bit[7] bit[6] bit[5] bit[4] bit[3] bit[2] bit[1] bit[0] default page ref r0 (00h) 0000000 left input volume livu linmute lizc linvol 010010111 19 r1 (01h) 0000001 right input volume rivu rinmute rizc rinvol 010010111 19 r2 (02h) 0000010 lout1 volume lo1vu lo1zc lout1vol[6:0] 001111001 31 r3 (03h) 0000011 rout1 volume ro1vu ro1zc rout1vol[6:0] 001111001 31 r4 (04h) 0000100 reserved 0 0 0 0 0 0 0 0 0 000000000 - r5 (05h) 0000101 adc & dac control adcdiv2 dacdiv2 adcpol[1:0] hpor dacmu deemph[1:0] adchpd 000001000 19,25,28 r6 (06h) 0000110 reserved 0 0 0 0 0 0 0 0 0 000000000 - r7 (07h) 0000111 audio interface 0 bclkinv ms lrswap lrp wl[1:0] format[1:0] 000001010 37 r8 (08h) 0001000 sample rate bcm[1:0] clkdiv2 sr[4:0] usb 000000000 39 r9 (09h) 0001001 reserved 0 0 0 0 0 0 0 0 0 000000000 - r10 (0ah) 0001010 left dac volume ldvu ldacvol[7:0] 011111111 26 r11 (0bh) 0001011 right dac volume rdvu rdacvol[7:0] 011111111 26 r12 (0ch) 0001100 bass contro l 0 bb bc 0 0 bass[3:0] 000001111 27 r13 (0dh) 0001101 treble control 0 0 tc 0 0 trbl[3:0] 000001111 27 r15 (0fh) 0001111 reset writing to this register resets all registers to their default state not reset - r16 (10h) 0010000 3d control 0 mode3d 3duc 3dlc 3ddepth[3:0] 3den 000000000 25 r17 (11h) 0010001 alc1 alcsel[1:0] maxgain[2:0] alcl[3:0] 001111011 23 r18 (12h) 0010010 alc2 0 alczc 0 0 0 hld[3:0] 000000000 23 r19 (13h) 0010011 alc3 0 dcy[3:0] atk[3:0] 000110010 23 r20 (14h) 0010100 noise gate 0 ngth[4:0] ngg[1:0] ngat 000000000 24 r21 (15h) 0010101 left adc volume lavu ladcvol[7:0] 011000011 21 r22 (16h) 0010110 right adc volume ravu radcvol[7:0] 011000011 21 r23 (17h) 0010111 additional contro l(1) tsden vsel[1:0] dmonomix[1:0] datsel[1:0] dacinv toen 011000000 18,19,28,33 r24 (18h) 0011000 additional control(2) lcomen hpcomen 0 0 0 tri lrcm adcosr dacosr 000000000 r25 (19h) 0011001 pwr mgmt (1) vmidsel[1:0] vref ainl ainr adcl adcr 0 digenb 000000000 43 r26 (1ah) 0011010 pwr mgmt (2) dacl dacr lout1 rout1 lout2 rout2 0 0 0 000000000 43 r27 (1bh) 0011011 additional control (3) 00 vroi hpflren 0 0 0 0 0 000000000 35 r31 (1fh) 0011111 adc input mode ds monomix[1:0] rdcm ldcm 0 0 0 0 000000000 17 r32 (20h) 0100000 adcl signal path 0 linsel[1:0] lmicboost[1:0] 0 0 0 0 000000000 17 r33 (21h) 0100001 adcr signal path 0 rinsel[1:0] rmicboost[1:0] 0 0 0 0 000000000 17 r34 (22h) 0100010 left out mix (1) ld2lo li2lo li2lovol[2:0] 0 lmixsel[2:0] 001010000 29 r35 (23h) 0100011 left out mix (2) rd2lo ri2lo ri2lovol[2:0] 0 0 0 0 001010000 29 r36 (24h) 0100100 right out mix (1) ld2ro li2ro li2rovol[2:0] 0 rmixsel[2 :0] 001010000 30 r37 (25h) 0100101 right out mix (2) rd2ro ri2ro ri2rovol[2:0] 0 0 0 0 001010000 30 r38 (26h) 0100110 reserved 0 0 1 0 1 0 0 0 0 001010000 30 r39 (27h) 0100111 reserved 0 0 1 0 1 0 0 0 0 001010000 30 r40 (28h) 0101000 lout2 volume lo2vu lo2zc lout2vol[6:0] 001111001 32 r41 (29h) 0101001 rout2 volume ro2vu ro2zc rout2vol[6:0] 001111001 32 r42 (2ah) 0101010 reserved 0 0 1 1 1 1 0 0 1 001111001 35 r67 (43h) 1000011 low power playback 0 0 0 0 0 dacmix bias 0 0 0 000000000 50 highlighting indicates bits or registers which differ from wm8750l / wm8750bl device family.
production data wm8988 w pd, rev 4.0, october 2008 47 digital filter characteristics the adc and dac employ different digital filters. there are 4 types of digital filter, called type 0, 1, 2 and 3. the performance of types 0 and 1 is listed in the table below, the responses of all filters is shown in the proceeding pages. parameter test conditions min typ max unit adc filter type 0 (usb mode, 250fs operation) +/- 0.05db 0 0.416fs passband -6db 0.5fs passband ripple +/- 0.05 db stopband 0.584fs stopband attenuation f > 0.584fs -60 db adc filter type 1 (usb mode, 272fs or normal mode operation) +/- 0.05db 0 0.4535fs passband -6db 0.5fs passband ripple +/- 0.05 db stopband 0.5465fs stopband attenuation f > 0.5465fs -60 db -3db 3.7 -0.5db 10.4 high pass filter corner frequency -0.1db 21.6 hz dac filter type 0 (usb mode, 250fs operation) +/- 0.03db 0 0.416fs passband -6db 0.5fs passband ripple +/-0.03 db stopband 0.584fs stopband attenuation f > 0.584fs -50 db dac filter type 1 (usb mode, 272fs or normal mode operation) +/- 0.03db 0 0.4535fs passband -6db 0.5fs passband ripple +/- 0.03 db stopband 0.5465fs stopband attenuation f > 0.5465fs -50 db table 43 digital filter characteristics dac filters adc filters mode group delay mode group delay 0 (250 usb) 11/fs 0 (250 usb) 13/fs 1 (256/272) 16/fs 1 (256/272) 23/fs 2 (250 usb, 96k mode) 4/fs 2 (250 usb, 96k mode) 4/fs 3 (256/272, 88.2/96k mode) 3/fs 3 (256/272, 88.2/96k mode) 5/fs table 44 adc/dac digital filters group delay terminology 1. stop band attenuation (db) ? the degree to which the frequency spectrum is attenuated (outside audio band) 2. pass-band ripple ? any variation of the frequency response in the pass-band region
wm8988 production data w pd, rev 4.0, october 2008 48 dac filter responses -100 -80 -60 -40 -20 0 0 0.5 1 1.5 2 2.5 3 response (db) frequency (fs) -0.06 -0.05 -0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 response (db) frequency (fs) figure 21 dac digital filter frequency response ? type 0 figure 22 dac digital filter ripple ? type 0 -100 -80 -60 -40 -20 0 0 0.5 1 1.5 2 2.5 3 response (db) frequency (fs) -0.06 -0.05 -0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 response (db) frequency (fs) figure 23 dac digital filter frequency response ? type 1 figure 24 dac digital filter ripple ? type 1 -100 -80 -60 -40 -20 0 0 0.5 1 1.5 2 2.5 3 response (db) frequency (fs) -0.06 -0.05 -0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0 0.05 0.1 0.15 0.2 0.25 response (db) frequency (fs) figure 25 dac digital filter frequency response ? type 2 figure 26 dac digital filter ripple ? type 2
production data wm8988 w pd, rev 4.0, october 2008 49 -100 -80 -60 -40 -20 0 0 0.5 1 1.5 2 2.5 3 response (db) frequency (fs) -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 0 0.05 0.1 0.15 0.2 0.25 response (db) frequency (fs) figure 27 dac digital filter frequency response ? type 3 figure 28 dac digital filter ripple ? type 3 adc filter responses -100 -80 -60 -40 -20 0 0 0.5 1 1.5 2 2.5 3 response (db) frequency (fs) -0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0.03 0.04 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 response (db) frequency (fs) figure 29 adc digital filter frequency response ? type 0 figure 30 adc digital filter ripple ? type 0 -100 -80 -60 -40 -20 0 0 0.5 1 1.5 2 2.5 3 response (db) frequency (fs) -0.06 -0.05 -0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 response (db) frequency (fs) figure 31 adc digital filter frequency response ? type 1 figure 32 adc digital filter ripple ? type 1
wm8988 production data w pd, rev 4.0, october 2008 50 -100 -80 -60 -40 -20 0 0 0.5 1 1.5 2 2.5 3 response (db) frequency (fs) -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 0 0.05 0.1 0.15 0.2 0.25 response (db) frequency (fs) figure 33 adc digital filter frequency response ? type 2 figure 34 adc digital filter ripple ? type 2 -100 -80 -60 -40 -20 0 0 0.5 1 1.5 2 2.5 3 response (db) frequency (fs) -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25 0 0.05 0.1 0.15 0.2 0.25 response (db) frequency (fs) figure 35 adc digital filter frequency response ? type 2 figure 36 adc digital filter ripple ? type 3 de-emphasis filter responses -10 -8 -6 -4 -2 0 0 2000 4000 6000 8000 10000 12000 14000 16000 response (db) frequency (fs) -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0 2000 4000 6000 8000 10000 12000 14000 16000 response (db) frequency (fs) figure 37 de-emphasis frequency response (32khz) figure 38 de-emphasis error (32khz)
production data wm8988 w pd, rev 4.0, october 2008 51 -10 -8 -6 -4 -2 0 0 5000 10000 15000 20000 response (db) frequency (fs) -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0 5000 10000 15000 20000 response (db) frequency (fs) figure 39 de-emphasis frequency response (44.1khz) figure 40 de-emphasis error (44.1khz) -10 -8 -6 -4 -2 0 0 5000 10000 15000 20000 response (db) frequency (fs) -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0 5000 10000 15000 20000 response (db) frequency (fs) figure 41 de-emphasis frequency response (48khz) figure 42 de-emphasis error (48khz) highpass filter the wm8988 has a selectable digital highpass filter in the adc filter path to remove dc offsets. the filter response is characterised by the following polynomial: figure 43 adc highpass filter response 1 - z -1 1 - 0.9995z -1 h(z) = -15 -10 -5 0 0 0.0005 0.001 0.0015 0.002 response (db) frequency (fs)
wm8988 production data w pd, rev 4.0, october 2008 52 applications information recommended external components dbvdd dcvdd avdd linput1 rinput1 mode csb sdin sclk linput2 rinput2 bclk lrc dacdat adcdat audio interface (i2s/lj/rj/dsp) dgnd agnd lout2 rout2 vref vmid wm8988 + + + c7 c19 c17 c8 c9 c10 + c22 c23 hpvdd hpgnd c4 c3 c2 c1 dvdd avdd mclk control interface (2 or 3-wire) high for 3-wire low for 2-wire lineout 4.7uf 1uf 1uf 1uf 1uf 4.7uf 4.7uf 10uf 4.7uf layout notes: lout1 rout1 + + c14 c15 headphones 220uf 220uf 16 or 32 ohm c21 4.7uf c20 4.7uf 10uf + + hpcom lcom gnd gnd gnd gnd gnd gnd gnd gnd 1. c1 to c4, c17, c19, c20 and c21 should be as close to the relative wm8988 connecting pin as possible. 2. for capacitors c7 to c10, c14, c15, c22 and c23 it is recommended that low esr components are used. 3. hpcom and lcom should be connected to gnd at the connector. 0.1uf 0.1uf figure 44 recommended external components diagram
production data wm8988 w pd, rev 4.0, october 2008 53 line input configuration when linput1/rinput1 or linput2/rinput2 are used as line inputs, the microphone boost and alc functions should normally be disabled. in order to avoid clipping, the user must ensure that the input signal does not exceed avdd. this may require a potential divider circuit in some applications. it is also recommended to remove rf interference picked up on any cables using a simple first-order rc filter, as high-frequency components in the input signal may otherwise cause aliasing distortion in the audio band. ac signals with no dc bias should be fed to the wm8988 through a dc blocking capacitor, e.g. 1 f. headphone output configuration analogue outputs lout1/rout1 and lout2/rout2, can drive a 16 ? or 32 ? headphone load, as shown in figure 45. figure 45 recommended headphone output configurations the dc blocking capacitors c1 and c2 and the load resistance together determine the lower cut-off frequency, f c . increasing the capacitance lowers f c , improving the bass response. smaller capacitance values will diminish the bass response. assuming a 16 ohm load and c1, c2 = 220 f: f c = 1 / 2 r l c 1 = 1 / (2 x 16 ? x 220 f) = 45 hz line output configuration the analogue outputs, lout1/rout1 and lout2/rout2, can be used as line outputs. recommended external components are shown below. figure 46 recommended circuit for line output the dc blocking capacitors and the load resistance together determine the lower cut-off frequency, f c . assuming a 10 k ? load and c1, c2 = 1 f: f c = 1 / 2 (r l +r 1 ) c 1 = 1 / (2 x 10.1k ? x 1 f) = 16 hz increasing the capacitance lowers f c , improving the bass response. smaller values of c1 and c2 will diminish the bass response. the function of r1 and r2 is to protect the line outputs from damage when used improperly.
wm8988 production data w pd, rev 4.0, october 2008 54 minimising pop noise at the analogue outputs to minimize any pop or click noise when the system is powered up or down, the following procedures are recommended. power up ? switch on power supplies. by default the wm8988 is in standby mode, the dac is digitally muted and the audio interface, line outputs and headphone outputs are all off (dacmu = 1 power management registers 1 and 2 are all zeros). ? enable vmid and vref. ? enable dacs as required ? enable line and / or headphone output buffers as required. ? set dacmu = 0 to soft-un-mute the audio dacs. power down ? set dacmu = 1 to soft-mute the audio dacs. ? disable all output buffers. ? switch off the power supplies. power management examples power management (1) power management (2) pgas adcs dacs output buffers operation mode vref ainl/r pgl pgr adl adr mbi dal dar lo1 ro1 lo2 ro2 stereo headphone playback 1 0 0 0 0 0 0 1 1 1 1 0 0 stereo line-in record 1 1 1 1 1 1 0 0 0 0 0 0 0 stereo microphone record 1 1 1 1 1 1 1 0 0 0 0 0 0 mono microphone record 1 1 1 0 1 0 1 0 0 0 0 0 0 stereo line-in to headphone out 1 1 0 0 0 0 0 0 0 1 1 0 0 table 45 register settings for power management
production data wm8988 w pd, rev 4.0, october 2008 55 package dimensions dm050.b fl: 28 pin col qfn plastic package 4 x 4 x 0.55 mm body, 0.45 mm lead pitch index area (d/2 x e/2) top view d e 4 notes: 1. dimension b applies to metallized terminal and is measured between 0.15 mm and 0.30 mm from terminal tip. 2. all dimensions are in millimetres. 3. coplanarity applies to the exposed heat sink slug as well as the terminals. 4. refer to applications note wan_0118 for further information regarding pcb footprints and qfn package soldering. 5. depending on the method of lead termination at the edge of the package, pull back (l1) may be present. 6. this drawing is subject to change without notice. detail 1 a 7 1 15 21 28 22 14 e 8 1 b c bbb m a bottom view c aaa 2 x c aaa 2 x c a3 seating plane detail 2 a1 c 0.08 c ccc a 5 side view l detail 1 e datum detail 2 terminal tip e/2 1 r see detail 2 b a3 g t h w exposed lead detail 2 l1 dimensions (mm) symbols min nom max note a a1 a3 0.500 0.550 0.600 0.05 0.025 0 0.152 ref b d e e l 0.28 0.18 4.00 0.45 bsc 0.40 ref 4.00 0.10 aaa bbb ccc ref: 0.15 0.10 jedec, mo-220 tolerances of form and position 0.23 h 0.076 ref 0.535 ref g t 0.076 ref w 0.230 ref 1 l1 0.05 ref 5 3.95 4.05 3.95 4.05 pin 1 identification 0.150mm square 0.275mm 0.275mm b
wm8988 production data w pd, rev 4.0, october 2008 56 important notice wolfson microelectronics plc (?wolfson?) products and services are sold subject to wolfson?s terms and conditions of sale, delivery and payment supplied at the time of order acknowledgement. wolfson warrants performance of its products to the specifications in effect at the date of shipment. wolfson reserves the right to make changes to its products and specifications or to discontinue any product or service without notice. customers should therefore obtain the latest version of relevant information from wolfson to verify that the information is current. testing and other quality control techniques are utilised to the extent wolfson deems necessary to support its warranty. specific testing of all parameters of each device is not necessarily performed unless required by law or regulation. in order to minimise risks associated with customer applications, the customer must use adequate design and operating safeguards to minimise inherent or procedural hazards. wolfson is not liable for applications assistance or customer product design. the customer is solely responsible for its selection and use of wolfson products. wolfson is not liable for such selection or use nor for use of any circuitry other than circuitry entirely embodied in a wolfson product. wolfson?s products are not intended for use in life support systems, appliances, nuclear systems or systems where malfunction can reasonably be expected to result in personal injury, death or severe property or environmental damage. any use of products by the customer for such purposes is at the customer?s own risk. wolfson does not grant any licence (express or implied) under any patent right, copyright, mask work right or other intellectual property right of wolfson covering or relating to any combination, machine, or process in which its products or services might be or are used. any provision or publication of any third party?s products or services does not constitute wolfson?s approval, licence, warranty or endorsement thereof. any third party trade marks contained in this document belong to the respective third party owner. reproduction of information from wolfson datasheets is permissible only if reproduction is without alteration and is accompanied by all associated copyright, proprietary and other notices (including this notice) and conditions. wolfson is not liable for any unauthorised alteration of such information or for any reliance placed thereon. any representations made, warranties given, and/or liabilities accepted by any person which differ from those contained in this datasheet or in wolfson?s standard terms and conditions of sale, delivery and payment are made, given and/or accepted at that person?s own risk. wolfson is not liable for any such representations, warranties or liabilities or for any reliance placed thereon by any person. address wolfson microelectronics plc westfield house 26 westfield road edinburgh eh11 2qb united kingdom tel :: +44 (0)131 272 7000 fax :: +44 (0)131 272 7001 email :: sales@wolfsonmicro.com

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