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pam8408 document number: ds36992 rev. 1 - 2 1 of 11 www.diodes.com june 2014 ? diodes incorporated pam8408 new product a product line of diodes incorporated 2x3w stereo differential input class d audio amplifier with memory up/down volume description the pam8408 is a filter-less class-d amplifier with high snr and differential input that helps el iminate noise. advanced 32-step up/down volume control minimize s external components and allows speaker volume control. the gain will held when the chip is in shutdown mode. the pam8408 supports 2.5v to 6v operation make it idea for up to 4 cells alkaline battery applications. features like greater than 87% efficiency and small pcb area make the pam8408 class-d amplifier ideal for portable applications. the output uses a filter-less archit ecture minimizing the number of external components and pcb area whilst providing a high performance, simple and lower cost system. the pam8408 built in auto recovery scp (short circuit protection) and thermal shutdown. the pam8408 is available in so-16l package. features ? 3w output at 10% thd with a 4 ? load and 5v supply ? 2.4w output at 1% thd with a 4 ? load and 5v supply ? 2.5v to 6.0v vdd operating ? fully differential input ? filter-less, low quiescent current and low emi ? low thd+n ? 32-step memory up/down volume control from -80db to 24db ? superior low noise: 60uv ? minimize pop/clip noise ? auto recovery short circuit protection ? thermal shutdown ? pb-free so-16l package pin assignments so-16l loutp loutn up vdd routp vdd routn gnd 15 9 10 11 12 13 14 16 gnd ri nn gnd down linn sd 1 2 3 4 5 6 7 8 pam8408 xxxywwll rinp linp applications ? pc speaker ? wireless speaker ? home sound systems ? active speakers ? docking stations typical applications circuit 6 gnd gnd 13 5 dow n 7 linn vdd 16 8 linp gnd 12 1 rinp routn 14 2 rinn routp 15 loutp 10 vdd 9 4 up 3 sd loutn 11 pam8408 01 . uf c6 v dd 4 ? 1uf c2 rinn 01 . uf c8 linp shdn on 01 . uf c5 rinp 01 . uf c7 linn 4 ? v dd 1uf c2
pam8408 document number: ds36992 rev. 1 - 2 2 of 11 www.diodes.com june 2014 ? diodes incorporated pam8408 new product a product line of diodes incorporated pin descriptions pin number pin name function 1 rinp positive input of right channel power amplifier 2 rinn negative input of right channel power amplifier 3 sd full chip shutdown control input (active low) 4 up volume up control (active low) ground connection 5 down volume down control (active low) 6,12,13 gnd ground 7 linn negative input of left channel power amplifier 8 linp positive input of left channel power amplifier 9,16 vdd power supply 10 loutp positive output of left channel power amplifier 11 loutn negative output of left channel power amplifier 14 routn negative output of right channel power amplifier 15 routp positive output of right channel power amplifier functional block diagram interface control attenuation decoder vdd rinp linn vdd gnd loutp loutn routn routp gnd modulator driver internal oscillator osc bias and references modulator driver thermal protection current protection down sd vdd + - rinn up + - linp vdd vdd absolute maximum ratings (@t a = +25c, unless otherwise specified.) parameter rating unit supply voltage (vdd) 6.5 v pins input voltage (sd, up, down, in) -0.3 to v dd +0.3 v storage temperature -65 to 150 c maximum junction temperature 150 c junction to ambient thermal resistance 40 c/w
pam8408 document number: ds36992 rev. 1 - 2 3 of 11 www.diodes.com june 2014 ? diodes incorporated pam8408 new product a product line of diodes incorporated recommended operating conditions (@t a = +25c, unless otherwise specified.) symbol parameter min max unit v dd supply voltage 2.5 6.0 v t a operating ambient temperature range -40 85 c t j junction temperature range -40 125 c electrical characteristics (@t a = +25c, v dd = 5v, gain = 24db, r l = 8 ? (33 h)+r+l(33 h), unless otherwise noted.) parameter symbol conditions min typ max units supply voltage range v dd 2.5 6.0 v quiescent current i q no load 8 ma output offset voltage v os no load 10 mv drain-source on-state resistance r ds(on) i ds = 0.5a p mosfet 0.3 ? n mosfet 0.2 output power p o thd+n = 1%, f = 1khz r l = 8 ? 1.4 w r l = 4 ? 2.4 total harmonic distortion plus noise thd+n r l = 8 ? p o =0.85w,f=1khz 0.08 % r l = 4 ? p o =1.75w,f=1khz 0.08 power supply ripple rejection psrr input ac-gnd, f=1khz, vpp=200mv 70 db channel separation cs p o =1w, f=1khz -95 db oscillator frequency f osc 200 250 300 khz efficiency p o = 1.1w, f = 1khz, r l = 8 ? 87 % p o = 2.4w, f = 1khz, r l = 4 ? 83 % noise vn input ac-gnd a-weighting 60 uv no a-weighting 80 signal noise ratio snr f = 20 - 20khz, thd = 1% 95 db turn-on time ton vdd = 5v 0.65 s mute current i mute mute = vdd 4 10 ma shutdown current i sd v sd = 0v 5 a logic input high v ih include sd,up,down 1.4 v logic input low v il include sd,up,down 0.6 v over temperature protection otp 150 c over temperature hysteresis oth 40 c
pam8408 document number: ds36992 rev. 1 - 2 4 of 11 www.diodes.com june 2014 ? diodes incorporated pam8408 new product a product line of diodes incorporated performance characteristics (@t a = +25c, v dd = 5v, gain = 24db, r l = 8 ? (33 h)+r+l(33 h), unless otherwise noted.) thd+n vs. output power (rl=8 ? ) thd+n vs. output power (rl=4 ? ) thd+n vs. frequency (rl=8 ? ) thd+n vs. frequency (rl=4 ? ) psrr vs. frequency crosstalk vs frequency 0.008 10 0.02 0.05 0.1 0.2 0.5 1 2 5 % 20 20k 50 100 200 500 1k 2k 5k 10k hz po=0.3w/0.5w/1w (red/pink/blue) 0.01 20 0.02 0.05 0.1 0.2 0.5 1 2 5 10 % 1m 3 2m 5m 10m 20m 50m 100m 200m 500m 1 2 w f=100hz/1khz/10khz (red/pink/blue) 0.01 40 0.02 0.05 0.1 0.2 0.5 1 2 5 10 20 % 1m 5 2m 5m 10m 20m 50m 100m 200m 500m 1 2 w f=100hz/1khz/10khz (red/pink/blue) 0.01 10 0.02 0.05 0.1 0.2 0.5 1 2 5 % 20 20k 50 100 200 500 1k 2k 5k 10k hz po=0.5w/1w/2w (red/pink/blue) -140 +0 -130 -120 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 d b 20 20k 50 100 200 500 1k 2k 5k 10k hz t r to l l to r -80 +0 -75 -70 -65 -60 -55 -50 -45 -40 -35 -30 -25 -20 -15 -10 -5 d b 20 20k 50 100 200 500 1k 2k 5k 10k hz
pam8408 document number: ds36992 rev. 1 - 2 5 of 11 www.diodes.com june 2014 ? diodes incorporated pam8408 new product a product line of diodes incorporated performance characteristics (cont.) (@t a = +25c, v dd = 5v, gain = 24db, r l = 8 ? (33 h)+r+l(33 h), unless otherwise noted.) frequency response noise floor efficiency vs. output power (rl = 8 ? ) efficiency vs. output power (rl = 4 ? ) output power vs. supply voltage (rl = 8 ? , thd = 10%) output power vs. supply voltage (rl = 4 ? ,thd = 10%) +0 +16 +2 +4 +6 +8 +10 +12 +14 d b g a 20 20k 50 100 200 500 1k 2k 5k 10k hz c in = 0.1f c in = 1f c in = 0.47f v dd = 5v v dd = 5v -140 +0 -130 -120 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 d b r a 20 20k 50 100 200 500 1k 2k 5k 10k hz
pam8408 document number: ds36992 rev. 1 - 2 6 of 11 www.diodes.com june 2014 ? diodes incorporated pam8408 new product a product line of diodes incorporated performance characteristics (cont.) (@t a = +25c, v dd = 5v, gain = 24db, r l = 8 ? (33 h)+r+l(33 h), unless otherwise noted.) quiescent current vs. supply voltage osc frequency vs. supply voltage rdson vs. output current up/down volume control (db) pmos nmos step gain step gain step gain 1 24 12 7.5 23 -10 2 22.5 13 6 24 -12 3 21 14 4.5 25 -14 4 19.5 15 3 26 -16 5 18 16 1.5 27 -18 6 16.5 17 0 28 -20 7 15 18 -1.5 29 -22 8 13.5 19 -3 30 -24 9 12* 20 -4.5 31 -26 10 10.36 21 -6 32 -80 11 9 22 -8 - - *default gain = 12db
pam8408 document number: ds36992 rev. 1 - 2 7 of 11 www.diodes.com june 2014 ? diodes incorporated pam8408 new product a product line of diodes incorporated application information maximum gain as shown in block diagram, the pam8408 has two internal amplifie rs stage. the first stage's gain is externally con-figurable, w hile the second stage's is internally fixed in a fixed-gain, inverting configur ation. the closed-loop gain of t he first stage is set by selecti ng the ratio of rf to ri while the second stage's gain is fixed at 2x. cons equently, the differential gain for the ic is a vd =20*log [2*(rf/ri)] the pam8408 sets maximum rf=218k ? and minimum ri=27k ? , thus the maximum closed-gain is 24db. up/down volume control (dvc) the pam8408 features a up/down volume control which consists of the up and down pins. an internal clock is used where the clock frequency value is determined from the following formula: f clk = f osc / 2 13 the oscillator frequency f osc value is 250khz typical with 20% tolerance. the dv c?s clock frequency is 30hz (cycle time 33ms) typical. volume changes are then effected by toggling either the up or down pins with a logic low. after a period of 1 cycle pulses with either the up or down pins held low, the volume will change to the next specified st ep, either up or down, and followed by a short delay. this d elay decreases the longer the line is held low, eventually r eaching a delay of zero. the delay allows the user to pull the up or down terminal low once for one volume change, or hold down to ramp several volume changes. the delay is optimally configured for push button volume control. if either the up or down pin remains low after the first volu me transition the volume will change again, but this time after 10 cycles. the followed transition occurs at 4 cycles for each volume transition. this is intended to provide the user with a volume control that pause s briefly after initial application, and then slowly increases the rate of volume change as it is continuously applied. this cycle is shown in the timi ng diagram shown in figure 1. there are 32 discrete gain settings ranging from +24db as maximum to -80db as minimum. upon device power on, the amplifier's ga in is set to a default value of 12db, and the gain will remain when applied a logic low to the sd pin, volume levels for each step vary and ar e specified in gain setting table on page 7. if both the up and down pins are held high, no volume change will occur. trigger points for the up and down pins are at 70% of vdd minimum for a logic high, and 20% of vdd maximum for a logic low. it is recommended, however, to toggle up and down between vdd and gnd for best performance. 1 cycle 10 cycles 4 cycles up/dn vol u me level 4 cycles figure 1 timming diagram shutdown operation in order to reduce power consumption while not in use, the pam 8408 contains shutdown ci rcuitry that is used to turn off the amp lifier's bias circuitry. this shutdown feature turns the amplifier off when l ogic low is placed on the sd pin. by switching the sd pin connec ted to gnd, the pam8408 supply current draw will be minimized in idle mode. the sd pin cannot be left floating due to the pull-down internal. power supply decoupling the pam8408 is a high performance cmos audio amplifier that re quires adequate power supply decoupling to ensure the output thd and psrr are as low as possible. power supply decoup ling is affecting low frequency response. opti mum decoupling is achieved by using tw o capacitors of different types that target different types of noise on the power supply leads. for higher fr equency transients, spikes, or dig ital hash on the line, a good low equivalent-series-resistance (esr) ce ramic capacitor, typically 1.0f, placed as close as possible to the device vdd t erminal works best. for filtering lower-frequency noise signals, a larger capacitor of 10f (ceramic) or greater placed near the audio power amplif ier is recommended.
pam8408 document number: ds36992 rev. 1 - 2 8 of 11 www.diodes.com june 2014 ? diodes incorporated pam8408 new product a product line of diodes incorporated application information (cont.) input capacitor (ci) large input capacitors are both expensive and space hungry for portable designs. clearly , a certain sized capacitor is needed t o couple in low frequencies without severe attenu-ation. but in many cases the sp eakers used in portable systems, whether internal or external, have little ability to reproduce signals below 100hz to 150hz. thus, using a large input capacitor may not increase actual system perfor-mance. in this case, input capacitor (ci) and input resistance (ri) of the amplifier form a high-pass filter with the corner frequency determined equation below, c ii 1 f= 2 rc in addition to system cost and size, click and pop perfor-mance is affected by the size of the input coupling capacitor, ci. a larger input coupling capacitor requires more charge to reach its quiescent dc voltage (nominally 1/2 vdd). this charge comes from the internal circu it via the feedback and is apt to create pops upon device enable. thus, by minimizing the capacitor size based on necessary low frequency response, turn- on pops can be minimized. under voltage lock-out (uvlo) the pam8408 incorporates circuitry designed to detect when the suppl y voltage is low. when the supply voltage drops to 2.4v or below, the pam8408 outputs are disable, and the device comes out of this stat e and starts to normal functional when the supply voltage inc reases. short circuit protection (scp) the pam8408 has short circuit protection ci rcuitry on the outputs that prevents dam age to the device during output-to-output an d output-to-gnd short. when a short circuit is detected on t he outputs, the outputs are disable immediat ely. if the short was removed, the devi ce activates again. over temperature protection thermal protection on the pam8408 prevents damage to the device wh en the internal die temperature exceeds 150c. there is a 15 degree tolerance on this trip point from device to device. once t he die temperature exceeds the thermal set point, the device outputs are disabled. this is not a latched fault. the thermal fault is cleared once the temperatur e of the die is reduced by 60c. this large hysteresis wil l prevent motor boating sound well and the device begins normal operation at th is point with no external system interaction. how to reduce emi (electro magnetic interference) a simple solution is to put an additional capacitor 1000f at powe r supply terminal for power line coupling if the traces from amplifier to speakers are short (<20cm). most applications require a ferrite bead filter which shows at figure 3. the ferrite filter reduces emi arou nd 1 mhz and higher. when selecting a ferrite bead, choose one with high impedance at high frequencies, but low impedance at low frequencies. 220pf 220pf out+ out- ferrite bead ferrite bead figure 3 ferrite bead filter to reduce emi
pam8408 document number: ds36992 rev. 1 - 2 9 of 11 www.diodes.com june 2014 ? diodes incorporated pam8408 new product a product line of diodes incorporated application information (cont.) pcb layout guidelines grounding at this stage it is paramount that we acknowledge the need for separate grounds. noise currents in the output power stage need to be returned to output noise ground and nowhere else. were these currents to circulate elsewhere, they may get into the power supply, the signa l ground, etc, worse yet, they may form a loop and radiate noise. any of thes e instances results in degraded amplifier performance. the logica l returns for the output noise currents associated with class d switching are the respective pgnd pins for each channel. the switch state diagram illustrates that pgnd is instrumental in nearly every switch state. this is the perfect point to which the output noise ground trace should retu rn. also note that output noise ground is channel specific. a two channels amplifier has two mutually exclusive c hannels and consequently must hav e two mutually exclusive output noise ground traces. the layout of the pam8408 o ffers separate pgnd connections fo r each channel and in some c ases each side of the bridge. output noise grounds must tie to system groun d at the power in exclusively. signal currents for the inputs, reference, etc need to be returned to quite ground. this ground only ties to the si gnal components and the gnd pin. gnd then ties to system ground. power supply line as same to the ground, vdd and each channel pvdd need to be separat ed and tied together at the system power supply. recommend t hat all the trace could be routed as short and th ick as possible. for the power line layout , just imagine water stream, any barricade p laced in the trace (shows in figure 4) could result in the bad performance of the amplifier. figure 4 components placement the power supply decoupling capacitors need to be placed as close to vdd pins as possi ble. the inputs need to be routed away fr om the noisy trace. ordering information pam8408 x x d: so-16l r: tape & real part number package standard package PAM8408DR so-16l 2,500units/tape&real shipping package package type
pam8408 document number: ds36992 rev. 1 - 2 10 of 11 www.diodes.com june 2014 ? diodes incorporated pam8408 new product a product line of diodes incorporated marking information loutp loutn up vdd routp vdd routn gnd 15 9 10 11 12 13 14 16 gnd ri nn gnd down linn sd 1 2 3 4 5 6 7 8 pam8408 xxxywwll rinp linp package outline dimensions (all dimensions in mm.) package: so-16l d e e1 e a 2 b a1 a c l symbol dimensions millimeters min max a - 1.260 a1 0.100 0.230 a2 1.020 - b 0.310 0.510 c 0.100 0.250 d 9.800 10.000 e 3.800 4.000 e1 5.800 6.200 e 1.270(typ) l 0.400 1.270 0o 8o pam8408: product code x: internal code y: year w: week ll: internal code
pam8408 document number: ds36992 rev. 1 - 2 11 of 11 www.diodes.com june 2014 ? diodes incorporated pam8408 new product a product line of diodes incorporated important notice diodes incorporated makes no warranty of any kind, express or implied, with regards to this document, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose (and their equivalents under the laws of any jurisdiction). diodes incorporated and its subsidiaries rese rve the right to make modifications, enhanc ements, improvements, corrections or ot her changes without further notice to this document and any product descri bed herein. diodes incorporated does not assume any liability ari sing out of the application or use of this document or any product described herein; neither does diodes incorporated convey any license under its patent or trademark rights, nor the rights of others. any customer or user of this document or products described herein in such applica tions shall assume all risks of such use and will agree to hold diodes incorporated and all the companies whose products are represented on diodes incorporated website, harmless against all damages. diodes incorporated does not warrant or accept any liability w hatsoever in respect of any products purchased through unauthoriz ed sales channel. should customers purchase or use diodes inco rporated products for any unintended or una uthorized application, customers shall i ndemnify and hold diodes incorporated and its representativ es harmless against all claims, damages, expenses, and attorney fees arising out of, directly or indirectly, any claim of personal injury or death a ssociated with such unintended or unauthorized application. products described herein may be covered by one or more united states, international or foreign patents pending. product names and markings noted herein may also be covered by one or more united states, international or foreign trademarks. this document is written in english but may be translated into multiple languages for reference. only the english version of t his document is the final and determinative format released by diodes incorporated. life support diodes incorporated products are specifically not authorized for use as critical com ponents in life support devices or systems without the express written approval of the chief executive offi cer of diodes incorporated. as used herein: a. life support devices or syst ems are devices or systems which: 1. are intended to implant into the body, or 2. support or sustain life and whose failure to perform when prope rly used in accordance with instructions for use provided in the labeling can be reasonably expected to re sult in significant injury to the user. b. a critical component is any component in a life support devic e or system whose failure to perform can be reasonably expect ed to cause the failure of the life support device or to affect its safety or effectiveness. customers represent that they have all necessary expertise in the safety and regulatory ramifi cations of their life support dev ices or systems, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-rel ated requirements concerning the ir products and any use of diodes incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or s ystems-related information or support that may be provided by diodes incorporated. further, customers must fully indemnify diodes incorporate d and its representatives against any damages arisi ng out of the use of diodes incorporated pr oducts in such safety-critical, life suppor t devices or systems. copyright ? 2014, diodes incorporated www.diodes.com

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