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19-3720; Rev 0; 11/06
1.5V to 3.6V, 416ksps, 1-Channel True-Differential/ 2-Channel Single-Ended, 8-Bit, SAR ADCs
General Description
The MAX1391/MAX1394 micropower, serial-output, 8-bit, analog-to-digital converters (ADCs) operate with a single power supply from +1.5V to +3.6V. These ADCs feature automatic shutdown, fast wake-up, and a highspeed 3-wire interface. Power consumption is only 0.743mW (VDD = +1.5V) at the maximum conversion rate of 416ksps. AutoShutdownTM between conversions reduces power consumption at slower throughput rates. The MAX1391/MAX1394 require an external reference V REF that has a wide range from 0.6V to V DD . The MAX1391 provides one true-differential analog input that accepts signals ranging from 0 to VREF (unipolar mode) or VREF/2 (bipolar mode). The MAX1394 provides two single-ended inputs that accept signals ranging from 0 to V REF . Analog conversion results are available through a 5MHz 3-wire SPITM-/QSPITM-/ MICROWIRETM-/digital signal processor (DSP)-compatible serial interface. Excellent dynamic performance, low voltage, low power, ease of use, and small package sizes make these converters ideal for portable battery-powered data-acquisition applications, as well as other applications that demand low-power consumption and minimal space. The MAX1391/MAX1394 are available in a space-saving (3mm x 3mm), 10-pin TDFN package. The parts operate over the extended (-40C to +85C) and military (-55C to +125C) temperature ranges.
Features
o 416ksps, 8-Bit Successive-Approximation Register (SAR) ADCs o Single True-Differential Analog Input Channel with Unipolar-/Bipolar-Selected Input (MAX1391) o Dual Single-Ended Input Channel with ChannelSelected Input (MAX1394) o 0.2 LSB INL, 0.2 LSB DNL, No Missing Codes o 0.25 LSB Total Unadjusted Error (TUE) o 49dB SINAD at 100kHz Input Frequency o Single-Supply Voltage (+1.5V to +3.6V) o 0.97mW at 416ksps, 1.8V o 0.230mW at 100ksps, 1.8V o 3.1W at 1ksps, 1.8V o < 1A Shutdown Current o External Reference (0.6V to VDD) o AutoShutdown Between Conversions o SPI-/QSPI-/MICROWIRE-/DSP-Compatible, 3- or 4-Wire Serial Interface o Small (3mm x 3mm), 10-Pin TDFN
MAX1391/MAX1394
Applications
Portable Datalogging Data Acquisition Medical Instruments Battery-Powered Instruments Process Control
Typical Operating Circuit and Pin Configurations appear at end of data sheet. AutoShutdown is a trademark of Maxim Integrated Products, Inc. SPI/QSPI are trademarks of Motorola, Inc. MICROWIRE is a trademark of National Semiconductor Corp.
Ordering Information
PART MAX1391ETB MAX1391MTB** MAX1394ETB MAX1394MTB** TEMP RANGE -40C to +85C -55C to +125C -40C to +85C -55C to +125C PIN-PACKAGE 10 TDFN-EP* 10 TDFN-EP* 10 TDFN-EP* 10 TDFN-EP* ANALOG INPUTS 1-CH DIFF 1-CH DIFF 2-CH S/E 2-CH S/E TOP MARK AOX -- APA -- PKG CODE T1033-1 T1033-1 T1033-1 T1033-1
*EP = Exposed pad. **Future product--contact factory for availability. ________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
1.5V to 3.6V, 416ksps, 1-Channel True-Differential/ 2-Channel Single-Ended, 8-Bit, SAR ADCs MAX1391/MAX1394
ABSOLUTE MAXIMUM RATINGS
VDD to GND ..............................................................-0.3V to +4V SCLK, CS, OE, CH1/CH2, UNI/BIP, DOUT to GND.........................................-0.3V to (VDD + 0.3V) AIN+, AIN-, AIN1, AIN2, REF to GND ........-0.3V to (VDD + 0.3V) Maximum Current into Any Pin .........................................50mA Continuous Power Dissipation (TA = +70C) 10-Pin TDFN (derate 18.5mW/C above +70C) ....1481.5mW Operating Temperature Ranges MAX139_E_ _...................................................-40C to +85C MAX139_M_ _ ................................................-55C to +125C Junction Temperature ......................................................+150C Storage Temperature Range .............................-60C to +150C Lead Temperature (soldering, 10s) .................................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VDD = +1.5V to +3.6V, VREF = VDD, CREF = 0.1F, fSCLK = 5MHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER DC ACCURACY (Note 2) Resolution Integral Nonlinearity Differential Nonlinearity Offset Error Gain Error Total Unadjusted Error Offset-Error Temperature Coefficient Gain-Error Temperature Coefficient Channel-to-Channel Offset Matching Channel-to-Channel Gain Matching Input Common-Mode Rejection DYNAMIC SPECIFICATIONS (Note 3) Signal-to-Noise Plus Distortion Signal-to-Noise Ratio Total Harmonic Distortion Spurious-Free Dynamic Range Intermodulation Distortion Channel-to-Channel Crosstalk Full-Power Bandwidth Full-Linear Bandwidth CONVERSION RATE Conversion Time tCONV 9 clock cycles per conversion 1.8 s SINAD SNR THD SFDR IMD fIN1 = 98kHz at -6.5dBFS, fIN2 = 102kHz at -6.5dBFS MAX1394 only -3dB point SINAD > 48dB MAX1391 MAX1394 -73 -70 4 200 150 49 49 -65 -66 dB dB dBc dBc dB dB MHz kHz CMR MAX1394 only MAX1394 only VCM = 0 to VDD, MAX1391 only TUE 25 0.06 0.05 0.05 0.1 Offset nulled INL DNL No missing code overtemperature 8 0.2 0.2 0.15 0.15 0.25 Bits LSB LSB LSB LSB LSB mLSB/C mLSB/C LSB LSB mV/V SYMBOL CONDITIONS MIN TYP MAX UNITS
2
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1.5V to 3.6V, 416ksps, 1-Channel True-Differential/ 2-Channel Single-Ended, 8-Bit, SAR ADCs
ELECTRICAL CHARACTERISTICS (continued)
(VDD = +1.5V to +3.6V, VREF = VDD, CREF = 0.1F, fSCLK = 5MHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER Throughput Rate Power-Up and Acquisition Time Aperture Delay Aperture Jitter Serial-Clock Frequency tACQ tAD tAJ fCLK Unipolar Bipolar, MAX1391 only, (AIN+ - AIN-) Bipolar, MAX1391 only, [(AIN+) + (AIN-)] / 2 Channel not selected, or conversion stopped, or in shutdown mode 16 VDD + 0.05 24 0.025 416ksps 20 2.5 60 0.3 x VDD 0.7 x VDD 0.06 x VDD IIL CIN Inputs at GND or VDD CS, OE CH1/CH2, UNI/BIP 1 12.5 0.1 x VDD 0.9 x VDD 1 10 1.5 3.6 1 0.1 0 -VREF/2 0 SYMBOL CONDITIONS 12 clocks per conversion, includes powerup acquisiton and conversion time Three SCLK cycles 600 8 30 5.0 VREF +VREF/2 VDD 1.5 MIN TYP MAX 416 UNITS ksps ns ns ps MHz
MAX1391/MAX1394
ANALOG INPUTS (AIN+, AIN-, AIN1, AIN2) Input Voltage Range Common-Mode Input Voltage Range Input Leakage Current Input Capacitance REFERENCE INPUT (REF) REF Input Voltage Range REF Input Capacitance REF DC Leakage Current REF Input Dynamic Current DIGITAL INPUTS (SCLK, CS, OE, CH1/CH2, UNI/BIP) Input-Voltage Low Input-Voltage High Input Hysteresis Input Leakage Current Input Capacitance DIGITAL OUTPUT (DOUT) Output-Voltage Low Output-Voltage High Tri-State Leakage Current Tri-State Output Capacitance POWER SUPPLY Positive Supply Voltage VDD V VOL VOH ILT COUT ISINK = 2mA ISOURCE = 2mA OE = VDD OE = VDD V V A pF VIL VIH V V V A pF VREF 0.6 V pF A A VIN VCM V V A pF
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3
1.5V to 3.6V, 416ksps, 1-Channel True-Differential/ 2-Channel Single-Ended, 8-Bit, SAR ADCs MAX1391/MAX1394
ELECTRICAL CHARACTERISTICS (continued)
(VDD = +1.5V to +3.6V, VREF = VDD, CREF = 0.1F, fSCLK = 5MHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER SYMBOL CONDITIONS fSAMPLE = 100ksps Positive Supply Current (Note 4) IDD fSAMPLE = 416ksps Power-down mode (Note 5) Power-down mode (Note 6) Power-Supply Rejection PSR VDD = 1.6V to 3.6V, full-scale input (Note 7) VDD = 1.6V VDD = 3V VDD = 1.6V VDD = 3V MIN TYP 125 150 520 710 5 0.2 150 MAX 150 200 600 800 10 2.5 1000 V/V A UNITS
TIMING CHARACTERISTICS
(VDD = +1.5V to +3.6V, VREF = VDD, CREF = 0.1F, fSCLK = 5MHz, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Figure 1)
PARAMETER SCLK Clock Period SCLK Pulse-Width High SCLK Pulse-Width Low CS Fall to SCLK Rise Setup SCLK Rise to CS Fall Ignore SCLK Fall to DOUT Valid OE Rise to DOUT Disable OE Fall to DOUT Enable CS Pulse-Width High and Low OE Pulse-Width High and Low CH1/CH2 Setup Time (to the First SCLK) CH1/CH2 Hold Time (to the First SCLK) UNI/BIP Setup Time (to the First SCLK) UNI/BIP Hold Time (to the First SCLK) SYMBOL tCP tCH tCL tCSS tCSO tDOV tDOD tDOE tCSW tOEW tCHS tCHH tUBS tUBH MAX1394 only MAX1394 only MAX1391 only MAX1391 only 80 80 10 0 10 0 CLOAD = 0 to 30pF CONDITIONS MIN 200 90 90 80 0 10 6 9 80 20 20 TYP MAX 10,000 UNITS ns ns ns ns ns ns ns ns ns ns ns ns ns ns
Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: Note 7:
Devices are production tested at room and +85C. Specification to -40C are guaranteed by design. VDD = 1.6V, VREF = 1.6V, and VAIN = 1.6V. VDD = 1.6V, VREF = 1.6V, VAIN = 1.6VP-P, fSCLK = 5MHz, fSAMPLE = 416ksps, and fIN (sine wave) = 100kHz. All digital inputs swing between VDD and GND. VREF = VDD, fIN = 100kHz sine wave, VAIN = VREFP-P, CLOAD = 30pF on DOUT. CS = VDD, OE = UNI/BIP = CH1/CH2 = VDD or GND, SCLK is active. CS = VDD, OE = UNI/BIP = CH1/CH2 = VDD or GND, SCLK is inactive. Change in VAIN at code boundary 254.5.
4
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1.5V to 3.6V, 416ksps, 1-Channel True-Differential/ 2-Channel Single-Ended, 8-Bit, SAR ADCs MAX1391/MAX1394
UNI/BIP OR CH1/CH2 tCHS OE tUBS tCHH tUBH tOEW CS tCSO SCLK tDOE tCP tDOV DOUT HIGH-Z tDOD HIGH-Z tCSS tCL tCH tCSW
Figure 1. Detailed Serial-Interface Timing Diagram
VDD
6k
DOUT DOUT
6k
50pF GND
50pF GND b) HIGH IMPEDANCE TO VOL, VOH TO VOL, AND VOL TO HIGH IMPEDANCE
a) HIGH IMPEDANCE TO VOH, VOL TO VOH, AND VOH TO HIGH IMPEDANCE
Figure 2. Load Circuits for Enable/Disable Times
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5
1.5V to 3.6V, 416ksps, 1-Channel True-Differential/ 2-Channel Single-Ended, 8-Bit, SAR ADCs MAX1391/MAX1394
Typical Operating Characteristics
(VDD = +1.6V, VREF = +1.6V, CREF = 0.1F, CL = 30pF, fSCLK = 5MHz. TA = +25C, unless otherwise noted.)
INL vs. CODE
MAX1391/94 toc01
INL ERROR vs. REFERENCE VOLTAGE
MAX1391/94 toc02
DNL vs. CODE
0.08 0.06 0.04 DNL (LSB) 0.02 0 -0.02 -0.04 VDD = 1.5V VREF = 1.5V
MAX1391/94 toc03 MAX1391/94 toc09 MAX1391/94 toc06
0.10 0.08 0.06 0.04 INL (LSB) 0.02 0 -0.02 -0.04 -0.06 -0.08 -0.10 0 32 64 96
0.10 0.08 0.06 INL ERROR (LSB) 0.04 0.02 0 -0.02 -0.04 -0.06 -0.08 -0.10 MIN INL MAX INL VDD = 3.6V
0.10
-0.06 -0.08 -0.10
128 160 192 224 256 CODE
0.6
1.1
1.6
2.1
2.6
3.1
3.6
0
32
64
96
128 160 192 224 256 CODE
REFERENCE VOLTAGE (V)
DNL ERROR vs. REFERENCE VOLTAGE
MAX1391/94 toc04
OFFSET ERROR vs. SUPPLY VOLTAGE
300 OFFSET ERROR (V) 200 100 0 -100 AIN1 -200 VREF = 1.5V TEMPERATURE = +25C AIN2
MAX1391/94 toc05
OFFSET ERROR vs. TEMPERATURE
400 300 OFFSET ERROR (V) 200 100 0 -100 -200 -300 VDD = 3.6V -400 AIN1 AIN2
0.10 0.08 0.06 DNL ERROR (LSB) 0.04 0.02 0 -0.02 -0.04 -0.06 -0.08 -0.10 0.6 1.1 1.6 2.1 2.6 3.1 MIN DNL MAX DNL VDD = 3.6V
400
-300 -400 3.6 1.5 1.8 2.1 2.4 2.7 3.0 3.3 3.6
-55
-25
5
35
65
95
125
REFERENCE VOLTAGE (V)
SUPPLY VOLTAGE (V)
TEMPERATURE (C)
OFFSET ERROR vs. REFERENCE VOLTAGE
MAX1391/94 toc07
GAIN ERROR vs. SUPPLY VOLTAGE
300 200 GAIN ERROR (V) 100 AIN2 0 -100 -200 -300 AIN1 VREF = 1.5V TEMPERATURE = +25C
MAX1391/94 toc08
GAIN ERROR vs. TEMPERATURE
400 VDD = 2.6V 300 200 GAIN ERROR (V) 100 0 -100 -200 -300 -400 AIN1 AIN2
400 300 OFFSET ERROR (V) 200 100 0 -100 -200 -300 VDD = 3.6V -400 0.6 1.1 1.6 2.1 2.6 3.1
400
-400 3.6 1.5 1.8 2.1 2.4 2.7 3.0 3.3 3.6 REFERENCE VOLTAGE (V) SUPPLY VOLTAGE (V)
-55
-25
5
35
65
95
125
TEMPERATURE (C)
6
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1.5V to 3.6V, 416ksps, 1-Channel True-Differential/ 2-Channel Single-Ended, 8-Bit, SAR ADCs MAX1391/MAX1394
Typical Operating Characteristics (continued)
(VDD = +1.6V, VREF = +1.6V, CREF = 0.1F, CL = 30pF, fSCLK = 5MHz. TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX1391/94 toc10 MAX1391/94 toc11
GAIN ERROR vs. REFERENCE VOLTAGE
400 VDD = 3.6V 300 200 GAIN ERROR (V) 100 0 -100 -200 -300 -400 0.6 1.1 1.6 2.1 2.5 3.0 3.5 REFERENCE VOLTAGE (V) 400 1.5 1.8 800
SUPPLY CURRENT vs. TEMPERATURE
VREF = 1.5V, CL = 33pF fSCLK = 5MHz, fSAMPLE = 416ksps AIN = FULL SCALE, 10kHz SINE WAVE
MAX1391/94 toc12
600
SUPPLY CURRENT (A)
600
SUPPLY CURRENT (A) VREF = 1.5V, CL = 33pF fSCLK = 5MHz, fSAMPLE = 416ksps AIN = FULL SCALE, 10kHz SINE WAVE 2.1 2.4 2.7 3.0 SUPPLY VOLTAGE (V) 3.3 3.6
700
550
500
500
450
400 -55 -25 5 35 65 95 125 TEMPERATURE (C)
SUPPLY CURRENT vs. CONVERSION RATE
MAX1391/94 toc13
SHUTDOWN CURRENT vs. SUPPLY VOLTAGE
MAX1391/94 toc14
SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE
MAX1391/94 toc15
800 fSCLK = 5MHz, fSAMPLE = 417ksps AIN = FULL SCALE, 100kHz SINE WAVE CL = 30pF SUPPLY CURRENT (A) 600 VDD = VREF = 3.0V 400
0.5
2.0 SHUTDOWN SUPPLY CURRENT (A)
SHUTDOWN CURRENT (A)
0.4
1.6
0.3
1.2 VDD = 3.6V 0.8 VDD = 1.8V 0.4
0.2
200
VDD = VREF = 1.6V
0.1
0 0 50 100 150 200 250 300 350 400 fSAMPLE (ksps)
0 1.5 1.8 2.1 2.4 2.7 3.0 3.3 3.6 VOLTAGE (V)
0 -55 -25 5 35 65 95 125 TEMPERATURE (C)
SCLK-TO-DOUT TIMING
MAX1391/94 toc16
FFT
VDD = 1.6V VREF = 1.6V fS = 417ksps fIN = 100.4kHz THD = -79.9dB SINAD = 49.0dB SFDR = -71.1dB
MAX1391/94 toc17
SAMPLING ERROR vs. SOURCE IMPEDANCE
AIN HIGH-TO-LOW FS TRANSITION
MAX1391/94 toc18
100 90 80 DOUT DELAY (ns) 70 60 50 40 30 20 10 0 0 100 200 300 CLOAD (pF) 400 500 VDD = 3.6V VDD = 1.5V
0 -20 MAGNITUDE (dB)
0.3 0.2 SAMPLING ERROR (LSB) 0.1 0 -0.1 AIN HIGH-TO-LOW FS TRANSITION -0.2 -0.3
-40
-60
-80
-100 600 0 20 40 60 80 100 120 140 FREQUENCY (kHz)
0
500
1000
1500
2000
2500
SOURCE IMPEDANCE ()
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7
1.5V to 3.6V, 416ksps, 1-Channel True-Differential/ 2-Channel Single-Ended, 8-Bit, SAR ADCs MAX1391/MAX1394
Pin Description
PIN MAX1391 1 2 -- 3 -- 4 5 MAX1394 1 -- 2 -- 3 4 5 NAME VDD AINAIN2 AIN+ AIN1 GND REF FUNCTION Positive Supply Voltage. Connect VDD to a 1.6V to 3.6V power supply. Bypass VDD to GND with a 0.1F capacitor as close as possible to the device. Negative Analog Input Analog Input Channel 2 Positive Analog Input Analog Input Channel 1 Ground External Reference Voltage Input. VREF = 0.6V to (VDD + 0.05V). Bypass REF to GND with a 0.1F capacitor as close as possible to the device. Input-Mode Select. Drive UNI/BIP high to select unipolar input mode. Pull UNI/BIP low to select bipolar input mode. In unipolar mode, the output data is in straight binary format. In bipolar mode, the output data is in two's complement format. Channel-Select Input. Pull CH1/CH2 low to select channel 1. Drive CH1/CH2 high to select channel 2. Active-Low Output Enable. Pull OE low to enable DOUT. Drive OE high to disable DOUT. Connect to CS to interface with SPI, QSPI, and MICROWIRE devices or set low to interface with DSP devices. Active-Low Chip-Select Input. A falling edge on CS initiates power-up and acquisition. Serial-Data Output. DOUT changes state on the falling edge of SCLK. DOUT is high impedance when OE is high. Serial-Clock Input. SCLK drives the conversion process and clocks data out. Acquisition ends on the 3rd falling edge after the CS falling edge. The LSB is clocked out on the SCLK 11th falling edge and the device enters AutoShutdown mode (see Figures 8, 9, and 10). Exposed Pad. Not internally connected. Connect the exposed pad to GND or leave floating.
6
--
UNI/BIP
--
6
CH1/CH2
7 8 9
7 8 9
OE CS DOUT
10 --
10 --
SCLK EP
Detailed Description
The MAX1391/MAX1394 use an input track and hold (T/H) circuit along with a SAR to convert an analog input signal to a serial 8-bit digital output data stream. The serial interface provides easy interfacing to microprocessors and DSPs. Figure 3 shows the simplified functional diagram for the MAX1391 (1 channel, true differential) and the MAX1394 (2 channels, single ended).
VDD
CONTROL LOGIC AND TIMING
CS SCLK OE
AIN+ (AIN1)* AIN- (AIN2)*
True-Differential Analog Input T/H
The equivalent input circuit of Figure 4 shows the MAX1391/MAX1394 input architecture that is composed of a T/H, a comparator, and a switched-capacitor DAC. The T/H enters its tracking mode on the falling edge of CS (while OE is held low). The positive input capacitor is connected to AIN+ (MAX1391), or to AIN1 or AIN2 (MAX1394). The negative input capacitor is connected to AIN- (MAX1391) or GND (MAX1394). The T/H enters its hold mode on the 3rd falling edge of SCLK and the dif8
INPUT MUX AND T/H
8-BIT SAR ADC
OUTPUT SHIFT REGISTER
DOUT
REF
UNI/BIP (CH1/CH2)* MAX1391 MAX1394 GND
*INDICATES THE MAX1394
Figure 3. Simplified Functional Diagram
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1.5V to 3.6V, 416ksps, 1-Channel True-Differential/ 2-Channel Single-Ended, 8-Bit, SAR ADCs
ference between the sampled positive and negative input voltages is converted. The time required for the T/H to acquire an input signal is determined by how quickly its input capacitance is charged. The required acquisition time lengthens as the input signal's source impedance increases. The acquisition time, tACQ, is the minimum time needed for the signal to be acquired. It is calculated by the following equation: tACQ 5.6 x (RSOURCE + RIN) x CIN + tPU where RSOURCE is the source impedance of the input signal. RIN = 500, which is the equivalent differential analog input resistance. CIN = 16pF, which is the equivalent differential analog input capacitance. tPU = 400ns. Note: tACQ is never less than 600ns and any source impedance below 400 does not significantly affect the ADC's AC performance.
Analog Input Bandwidth
The ADC's input-tracking circuitry has a 4MHz fullpower bandwidth, making it possible to digitize highspeed transient events and measure periodic signals with bandwidths exceeding the ADC's sampling rate by using undersampling techniques. Use anti-alias filtering to avoid high-frequency signals being aliased into the frequency band of interest.
MAX1391/MAX1394
Analog Input Range and Protection
The MAX1391/MAX1394 produce a digital output that corresponds to the analog input voltage as long as the analog inputs are within their specified range. When operating the MAX1391 in unipolar mode (UNI/BIP = 1), the specified differential analog input range is from 0 to VREF. When operating in bipolar mode (UNI/BIP = 0), the differential analog input range is from -VREF/2 to +VREF/2 with a common-mode range of 0 to VDD. The MAX1394 has an input range from 0 to VREF. Internal protection diodes confine the analog input voltage within the region of the analog power input rails (VDD, GND) and allow the analog input voltage to swing from GND - 0.3V to VDD + 0.3V without damage. Input voltages beyond GND - 0.3V and VDD + 0.3V forward bias the internal protection diodes. In this situation, limit the forward diode current to less than 50mA to avoid damage to the MAX1391/MAX1394.
RSOURCE
REF GND AIN2 AIN1 (AIN+)* CIN+
DAC
MAX1391 MAX1394 COMPARATOR + -
Output Data Format
Figures 8, 9, and 10 illustrate the conversion timing for the MAX1391/MAX1394. Twelve SCLK cycles are required to read the conversion result and data on DOUT transitions on the falling edge of SCLK. The conversion result contains 4 zeros, followed by 8 data bits with the data in MSB-first format. For the MAX1391, data is straight binary for unipolar mode and two's complement for bipolar mode. For the MAX1394, data is always straight binary.
ANALOG SIGNAL SOURCE
HOLD GND (AIN-)* CINRINHOLD VDD/2 TRACK RIN+ HOLD
Transfer Function
Figure 5 shows the unipolar transfer function for the MAX1391/MAX1394. Figure 6 shows the bipolar transfer function for the MAX1391. Code transitions occur halfway between successive-integer LSB values.
(*INDICATES THE MAX1391)
Figure 4. Equivalent Input Circuit
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9
1.5V to 3.6V, 416ksps, 1-Channel True-Differential/ 2-Channel Single-Ended, 8-Bit, SAR ADCs MAX1391/MAX1394
FF FE FD OUTPUT CODE (hex) FC FB FS = VREF ZS = 0 1 LSB = VREF 256 OUTPUT CODE (hex) 7E FULL-SCALE TRANSITION 7F +FS = VREF 2 ZS = 0 -VREF 2 V 1 LSB = REF 256 -FS = FULL-SCALE TRANSITION
01 00 FF FE
04 03 02 01 00 0 1 2 3 FS - 1.5 LSB INPUT VOLTAGE (LSB) 4 FS
81 80 -FS 0 -FS + 0.5 LSB +FS - 1.5 LSB INPUT VOLTAGE (LSB) +FS
Figure 5. Unipolar Transfer Function
Figure 6. Bipolar Transfer Function
Applications Information
Starting a Conversion
A falling edge on CS initiates the power-up sequence and begins acquiring the analog input as long as OE is also asserted low. On the 3rd SCLK falling edge, the analog input is held for conversion. The most significant bit (MSB) decision is made and clocked onto DOUT on the 4th SCLK falling edge. Valid DOUT data is available to be clocked into the master (microcontroller (C)) on the following SCLK rising edge. The rest of the bits are decided and clocked out to DOUT on each successive SCLK falling edge. See Figures 8 and 9 for conversion timing diagrams. Once a conversion has been initiated, CS can go high at any time. Further falling edges of CS do not reinitiate an acquisition cycle until the current conversion completes. Once a conversion completes, the first falling edge of CS begins another acquisition/conversion cycle.
Selecting Unipolar or Bipolar Mode (MAX1391 Only)
Drive UNI/BIP high to select unipolar mode or pull UNI/BIP low to select bipolar mode. UNI/BIP can be connected to VDD for logic-high, to GND for logic-low, or actively driven. UNI/BIP needs to be stable for tUBS prior to the first rising edge of SCLK after the CS falling edge (see Figure 1) for a valid conversion result when being actively driven.
Selecting Analog Input AIN1 or AIN2 (MAX1394 Only)
Pull CH1/CH2 low to select AIN1 or drive CH1/CH2 high to select AIN2 for conversion. CH1/CH2 can be connected to VDD for logic-high, to GND for logic-low, or actively driven. CH1/CH2 needs to be stable for tCHS prior to the first rising edge of SCLK after the CS falling edge (see Figure 1) for a valid conversion result when being actively driven.
10
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1.5V to 3.6V, 416ksps, 1-Channel True-Differential/ 2-Channel Single-Ended, 8-Bit, SAR ADCs
AutoShutdown Mode
The ADC automatically powers down on the SCLK falling edge that clocks out the LSB. This is the falling edge after the 11th SCLK. DOUT goes low when the LSB has been clocked into the master (C) on the 16th rising SCLK edge. Alternatively, drive OE high to force the MAX1391/ MAX1394 into power-down. Whenever OE goes high, the ADC powers down and disables DOUT regardless of CS, SCLK, or the state of the ADC. DOUT enters a high-impedance state after tDOD. 0.1F capacitor to GND for best performance (see the Typical Operating Circuit).
MAX1391/MAX1394
Serial Interface
The MAX1391/MAX1394 serial interface is fully compatible with SPI, QSPI, and MICROWIRE (see Figure 7). If a serial interface is available, set the C's serial interface in master mode so the C generates the serial clock. Choose a clock frequency between 100kHz and 5MHz. CS and OE can be connected together and driven simultaneously. OE can also be connected to GND if the DOUT bus is not shared and driven independently. SPI and MICROWIRE When using SPI or MICROWIRE, make the C the bus master and set CPOL = 0 and CPHA = 0 or CPOL = 1 and CPHA = 1. (These are the bits in the SPI or MICROWIRE control register.) Two consecutive 1-byte reads are required to get the entire 8-bit result from the ADC. The MAX1391/MAX1394 shut down after clocking out the LSB. DOUT then becomes high impedance. DOUT transitions on SCLK's falling edge and is clocked into the C on the SCLK's rising edge. See Figure 7 for connections and Figures 8 and 9 for timing diagrams. The conversion result contains 4 zeros, followed by the 8 data bits with the data in MSB-first format. When using CPOL = 0 and CPHA = 0 or CPOL = 1 and CPHA = 1, the MSB of the data is clocked into the C on the SCLK's fifth rising edge. To be compatible with SPI and MICROWIRE, connect CS and OE together and drive simultaneously. QSPI Unlike SPI, which requires two 1-byte reads to acquire the 8 bits of data from the ADC, QSPI allows the minimum number of clock cycles necessary to clock in the data. The MAX1391/MAX1394 require a minimum of 12 clock cycles from the C to clock out the 8 bits of data. See Figure 7 for connections and Figures 8 and 9 for timing diagrams. The conversion result contains 4 zeros, followed by the 8 data bits with the data in MSBfirst format. The MAX1391/MAX1394 shut down after clocking out the LSB. DOUT then becomes high impedance. When using CPOL = 0 and CPHA = 0 or CPOL = 1 and CPHA = 1, the MSB of the data is clocked into the C on the SCLK's fifth rising edge. To be compatible with QSPI, connect CS and OE together and drive simultaneously.
External Reference
The MAX1391/MAX1394 use an external reference between 0.6V and (VDD + 50mV). Bypass REF with a
I/O SCK
OE CS SCLK MAX1391
MAX1394
MISO I/O DOUT UNI/BIP (CH1/CH2)*
a) SPI
CS SCK
OE CS SCLK MAX1391
MAX1394
MISO I/O DOUT UNI/BIP (CH1/CH2)*
b) QSPI
I/O SK
OE CS SCLK MAX1391
MAX1394
SI I/O DOUT UNI/BIP (CH1/CH2)*
DSP Interface
c) MICROWIRE *INDICATES THE MAX1394
Figure 10 shows the timing for DSP operation. Figure 11 shows the connections between the MAX1391/ MAX1394 and several common DSPs.
Figure 7. Common Serial-Interface Connections to the MAX1391/MAX1394 ______________________________________________________________________________________ 11
1.5V to 3.6V, 416ksps, 1-Channel True-Differential/ 2-Channel Single-Ended, 8-Bit, SAR ADCs MAX1391/MAX1394
SAMPLING INSTANT ADC STATE UNI/BIP (CH1/CH2)* POWERDOWN POWER-UP AND ACQUIRE (tACQ) BIPOLAR (AIN1)* HOLD AND CONVERT (tCONV) POWER-DOWN UNI (AIN2)*
CS = OE 1 SCLK HIGH-Z HIGH-Z 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1
DOUT
D7
D6
D5
D4
D3
D2
D1
D0
*INDICATES THE MAX1394
Figure 8. Serial-Interface Timing for SPI/QSPI (CPOL = CPHA = 1) and MICROWIRE (G6 = 0, G5 = 1)
SAMPLING INSTANT ADC STATE UNI/BIP (CH1/CH2)* POWERDOWN POWER-UP AND ACQUIRE (tACQ) BIPOLAR (AIN1)* HOLD AND CONVERT (tCONV) POWER-DOWN UNI (AIN2)*
CS = OE 1 SCLK HIGH-Z HIGH-Z 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1
DOUT
D7
D6
D5
D4
D3
D2
D1
D0
*INDICATES THE MAX1394
Figure 9. Serial-Interface Timing for SPI/QSPI (CPOL = CPHA = 0) and MICROWIRE (G6 = 0, G5 = 0)
12
______________________________________________________________________________________
1.5V to 3.6V, 416ksps, 1-Channel True-Differential/ 2-Channel Single-Ended, 8-Bit, SAR ADCs MAX1391/MAX1394
SAMPLING INSTANT ADC STATE OE POWERDOWN POWER-UP AND ACQUIRE (tACQ) HOLD AND CONVERT (tCONV) POWERDOWN
UNI/BIP (CH1/CH2)* CS 16 SCLK 1
BIPOLAR (AIN1)*
UNI (AIN2)*
FS 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 2
DOUT
D7
D6
D5
D4
D3
D2
D1
D0
*INDICATES THE MAX1394
Figure 10. DSP Serial-Timing Diagram
As shown in Figure 11, drive the MAX1391/MAX1394 chip-select input (CS) with the DSP's frame-sync signal. OE may be connected to GND or driven independently. For continuous conversion operation, keep OE low and make the CS falling edge coincident with the 16th falling edge of the SCLK.
Unregulated Two-Cell or Single Lithium LiMnO2 Cell Operation
Low operating voltage (1.5V to 3.6V) and ultra-low-power consumption make the MAX1391/MAX1394 ideal for low cost, unregulated, battery-powered applications without the need for a DC-DC converter. Power the MAX1391/ MAX1394 directly from two alkaline/NiMH/NiCd cells in series or a single lithium coin cell as shown in the Typical Operating Circuit. Fresh alkaline cells have a voltage of approximately 1.5V per cell (3V with 2 cells in series) and approach end of life at 0.8V (1.6V with 2 cells in series). A typical 2 x AA alkaline discharge curve is shown in Figure 12a. A typical CR2032 lithium (LiMnO2) coin cell discharge curve is shown in Figure 12b.
Figure 13 shows the recommended system ground connections. Establish a single-point analog ground (star ground point) at the MAX1391/MAX1394s' GND pin or use the ground plane. High-frequency noise in the power supply (V DD ) degrades the ADC's performance. Bypass VDD to GND with a 0.1F capacitor as close to the device as possible. Minimize capacitor lead lengths for best supply noise rejection. To reduce the effects of supply noise, a 10 resistor can be connected as a lowpass filter to attenuate supply noise.
Exposed Pad
The MAX1391/MAX1394 TDFN package has an exposed pad on the bottom of the package. This pad is not internally connected. Connect the exposed pad to the GND pin on the MAX1391/MAX1394 or leave floating for proper electrical performance.
Definitions
Integral Nonlinearity (INL)
INL is the deviation of the values on an actual transfer function from a straight line. For the MAX1391/ MAX1394, this straight line is between the end points of the transfer function once offset and gain errors have been nullified. INL deviations are measured at every step and the worst-case deviation is reported in the Electrical Characteristics section.
Layout, Grounding, and Bypassing
For best performance, use PCBs. Board layout must ensure that digital and analog signal lines are separated from each other. Do not run analog and digital (especially clock) lines parallel to one another, or digital lines underneath the ADC package.
______________________________________________________________________________________
13
1.5V to 3.6V, 416ksps, 1-Channel True-Differential/ 2-Channel Single-Ended, 8-Bit, SAR ADCs MAX1391/MAX1394
I/O FSX FSR CLKX CLKR DR I/O DOUT UNI/BIP (CH1/CH2)* OE CS
3.0 2.8 2.6 VOLTAGE (V) 2.4 2.2 2.0
MAX1391 SCLK MAX1394
a) TMS320C541 CONNECTION DIAGRAM
1.8
I/O TFS RFS SCLK DR I/O SCLK DOUT UNI/BIP (CH1/CH2)* OE CS
TA = +25C 1.6 0 100 200 300 400 500 600 700
MAX1391 MAX1394
DAYS
Figure 12a. Typical 2 x AA Discharge Curve at 100ksps
3.0
b) ADSP218x CONNECTION DIAGRAM
2.8
I/O SC2 SLK SDR I/O OE CS SCLK DOUT
2.6 VOLTAGE (V)
MAX1391 MAX1394
2.4 2.2 2.0
UNI/BIP (CH1/CH2)*
1.8 TA = +25C 1.6
c) DSP563xx CONNECTION DIAGRAM *INDICATES THE MAX1394 ONLY
0
10
20 DAYS
30
40
50
Figure 11. Common DSP Connections to the MAX1391/MAX1394
Figure 12b. Typical CR2032 Discharge Curve at 100ksps
Differential Nonlinearity (DNL)
DNL is the difference between an actual step width and the ideal value of 1 LSB. A DNL error specification less than 1 LSB guarantees no missing codes and a monotonic transfer function. For the MAX1391/ MAX1394, DNL deviations are measured at every step and the worst-case deviation is reported in the Electrical Characteristics section.
Signal-to-Noise Plus Distortion (SINAD)
SINAD is computed by taking the ratio of the RMS signal to the RMS noise plus the RMS distortion. RMS noise includes all spectral components to the Nyquist frequency excluding the fundamental, the first five harmonics (HD2-HD6), and the DC offset. RMS distortion includes the first five harmonics (HD2-HD6).
SIGNALRMS SINAD = 20 x log 2 2 NOISE RMS + DISTORTIONRMS
14
______________________________________________________________________________________
1.5V to 3.6V, 416ksps, 1-Channel True-Differential/ 2-Channel Single-Ended, 8-Bit, SAR ADCs
POWER SUPPLY VDD 10 (OPTIONAL) STAR GROUND POINT VDD GND
where V1 is the fundamental amplitude, and V2 through V6 are the amplitudes of the 2nd- through 6th-order harmonics.
MAX1391/MAX1394
Spurious-Free Dynamic Range (SFDR)
SFDR is a dynamic figure of merit that indicates the lowest usable input signal amplitude. SFDR is the ratio of the RMS amplitude of the fundamental (maximum signal component) to the RMS value of the next-largest spurious component, excluding DC offset. SFDR is specified in decibels relative to the carrier (dBc).
Intermodulation Distortion (IMD)
VDD GND DATA DVDD DGND
MAX1391/MAX1394
DIGITAL CIRCUITRY
IMD is the ratio of the RMS sum of the intermodulation products to the RMS sum of the two fundamental input tones. This is expressed as:
VIM12 + VIM22 + ..... + VIM32 + VIMN2 IMD = 20 x log V12 + V22
Figure 13. Power-Supply Grounding Connections
Signal-to-Noise Ratio (SNR)
SNR is a dynamic figure of merit that indicates the converter's noise performance. For a waveform perfectly reconstructed from digital samples, the theoretical maximum SNR is the ratio of the full-scale analog input (RMS value) to the RMS quantization error (residual error). The ideal, theoretical minimum analog-to-digital noise is caused by quantization error only and results directly from the ADC's resolution (N bits): SNRdB[max] = 6.02dB x N + 1.76dB In reality, there are other noise sources such as thermal noise, reference noise, and clock jitter that also degrade SNR. SNR is computed by taking the ratio of the RMS signal to the RMS noise. RMS noise includes all spectral components to the Nyquist frequency excluding the fundamental, the first five harmonics, and the DC offset.
The fundamental input tone amplitudes (V1 and V2) are at -6.5dBFS. 14 intermodulation products (V IM_) are used in the MAX1391/MAX1394 IMD calculation. The intermodulation products are the amplitudes of the output spectrum at the following frequencies, where f IN1 and fIN2 are the fundamental input tone frequencies: * 2nd-order intermodulation products: fIN1 + fIN2, fIN2 - fIN1 * 3rd-order intermodulation products: 2 x fIN1 - fIN2, 2 x fIN2 - fIN1, 2 x fIN1 + fIN2, 2 x fIN2 + fIN1 * 4th-order intermodulation products: 3 x fIN1 - fIN2, 3 x fIN2 - fIN1, 3 x fIN1 + fIN2, 3 x fIN2 + fIN1 * 5th-order intermodulation products: 3 x fIN1 - 2 x fIN2, 3 x fIN2 - 2 x fIN1, 3 x fIN1 + 2 x fIN2, 3 x fIN2 + 2 x fIN1
Channel-to-Channel Crosstalk
Channel-to-channel crosstalk indicates how well each analog input is isolated from the others. The channel-tochannel crosstalk for the MAX1394 is measured by applying DC to channel 2 while a sine wave is applied to channel 1. An FFT is taken for channels 1 and 2, and the difference (in dB) is reported as the channel-tochannel crosstalk.
Total Harmonic Distortion (THD)
THD is a dynamic figure of merit that indicates how much harmonic distortion the converter adds to the signal. THD is the ratio of the RMS sum of the first five harmonics of the fundamental signal to the fundamental itself. This is expressed as:
2 2 2 2 2 V2 + V3 + V4 + V5 + V6 THD = 20 x log V1
Aperture Delay
The MAX1391/MAX1394 sample data on the falling edge of its third SCLK cycle (Figure 14). In actuality, there is a small delay between the falling edge of the sampling clock and the actual sampling instant. Aperture delay (tAD) is the time defined between the
15
______________________________________________________________________________________
1.5V to 3.6V, 416ksps, 1-Channel True-Differential/ 2-Channel Single-Ended, 8-Bit, SAR ADCs MAX1391/MAX1394
falling edge of the sampling clock and the instant when an actual sample is taken.
Aperture Jitter
Aperture jitter (tAJ) is the sample-to-sample variation in the aperture delay (Figure 14).
SCLK
THIRD FALLING EDGE
DC Power-Supply Rejection Ratio (PSRR)
DC PSRR is defined as the change in the positive fullscale transfer function point caused by a full range variation in the analog power-supply voltage (VDD).
tAD ANALOG INPUT tAJ SAMPLED DATA T/H (INTERNAL SIGNAL)
Chip Information
TRANSISTOR COUNT: 9106 PROCESS: BiCMOS
TRACK
HOLD
Figure 14. T/H Aperture Timing
Typical Operating Circuit
0.1F
2 x AA CELLS REF INPUT VOLTAGE
VDD REF 0.1F + MAX1391 MAX1394 AIN+ (AIN1)* AIN- (AIN2)* GND OE CS SCLK DOUT UNI/BIP (CH1/CH2)* SS SCL MISO CPU
INPUT VOLTAGE
*INDICATES THE MAX1394
16
______________________________________________________________________________________
1.5V to 3.6V, 416ksps, 1-Channel True-Differential/ 2-Channel Single-Ended, 8-Bit, SAR ADCs MAX1391/MAX1394
Pin Configurations
DOUT SCLK DOUT SCLK CH1/CH2 6 5 REF
CS
CS 8 3 AIN1
TOP VIEW
UNI/BIP
TOP VIEW
OE
10
9
8
7
6
10
9
MAX1391
MAX1394
1 VDD
2 AIN-
3 AIN+
4 GND
5 REF
1 VDD
2 AIN2
3mm x 3mm TDFN
3mm x 3mm TDFN
______________________________________________________________________________________
GND
OE 7 4
17
1.5V to 3.6V, 416ksps, 1-Channel True-Differential/ 2-Channel Single-Ended, 8-Bit, SAR ADCs MAX1391/MAX1394
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
6, 8, &10L, DFN THIN.EPS
PACKAGE OUTLINE, 6,8,10 & 14L, TDFN, EXPOSED PAD, 3x3x0.80 mm
21-0137
H
1 2
COMMON DIMENSIONS SYMBOL A D E A1 L k A2 MIN. 0.70 2.90 2.90 0.00 0.20 MAX. 0.80 3.10 3.10 0.05 0.40
PACKAGE VARIATIONS PKG. CODE T633-1 T633-2 T833-1 T833-2 T833-3 T1033-1 T1033-2 T1433-1 T1433-2 N 6 6 8 8 8 10 10 14 14 D2 1.50-0.10 1.50-0.10 1.50-0.10 1.50-0.10 1.50-0.10 1.50-0.10 1.50-0.10 1.70-0.10 1.70-0.10 E2 2.30-0.10 2.30-0.10 2.30-0.10 2.30-0.10 2.30-0.10 2.30-0.10 2.30-0.10 2.30-0.10 2.30-0.10 e 0.95 BSC 0.95 BSC 0.65 BSC 0.65 BSC 0.65 BSC 0.50 BSC 0.50 BSC 0.40 BSC 0.40 BSC JEDEC SPEC MO229 / WEEA MO229 / WEEA MO229 / WEEC MO229 / WEEC MO229 / WEEC MO229 / WEED-3 MO229 / WEED-3 ------b 0.40-0.05 0.40-0.05 0.30-0.05 0.30-0.05 0.30-0.05 0.25-0.05 0.25-0.05 0.20-0.05 0.20-0.05 [(N/2)-1] x e 1.90 REF 1.90 REF 1.95 REF 1.95 REF 1.95 REF 2.00 REF 2.00 REF 2.40 REF 2.40 REF
0.25 MIN. 0.20 REF.
PACKAGE OUTLINE, 6,8,10 & 14L, TDFN, EXPOSED PAD, 3x3x0.80 mm
-DRAWING NOT TO SCALE-
21-0137
H
2 2
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
18 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2006 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

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