19-0924; Rev 1; 4/09 KIT ATION EVALU E L B AVAILA Ultra-Low Offset/Drift, Precision Instrumentation Amplifiers with REF Buffer The MAX4208/MAX4209 ultra-low offset and drift instrumentation amplifiers feature exceptional precision specifications, low power consumption, rail-to-rail output, excellent gain-bandwidth product, and buffered REFIN/MODE input in a very small MAX(R) package. These devices use a spread-spectrum, autozeroing technique that constantly measures and corrects the input offset, eliminating drift over time and temperature and the effect of 1/f noise. This technique achieves less than 20V offset voltage, allows ground-sensing capability, provides ultra-low CMOS input bias current and increased common-mode rejection performance. The MAX4208/MAX4209 provide high-impedance inputs optimized for small-signal differential voltages (100mV). All devices provide a gain-bandwidth product of 750kHz. The MAX4208 provides an adjustable gain with two external resistors or unity gain with FB connected to OUT. The MAX4209 is available with a fixed gain of 100V/V with 0.03% (typ) accuracy. Both devices include a reference input (REF) to level-shift the output, allowing for bipolar signals in single-supply applications. In both devices, REFIN/MODE is an input to a precision unity-gain buffer, which sets the REF voltage to level-shift the output. The internal REF buffer allows the reference to be set by a simple resistive divider or an ADC reference without any loading error. The MAX4208/MAX4209 operate with a 2.85V to 5.5V single-supply voltage and consume only 750A of quiescent current (when the internal buffer is off) and only 1.4A in shutdown mode. These amplifiers also operate with 2.5V dual supplies with REF connected to ground and REFIN/MODE to V SS . The MAX4208/MAX4209 are available in space-saving 8-pin MAX packages and are specified over the automotive operating temperature range (-40C to +125C). Applications Automotive Transducer Applications Strain-Gauge Amplifiers Features Ultra-Low Input Offset Voltage 20V (max) at +25C 0.25% (max) Gain Error Low 0.2V/C Offset Voltage Drift 1pA CMOS Input Bias Current True Ground Sensing with Rail-to-Rail Output Buffered REF Input for High Accuracy and Bipolar Operation 2.85V to 5.5V Single-Supply Operation (or 1.425V to 2.75V Dual Supplies) 750A Supply Current 1.4A Shutdown Mode 750kHz Gain-Bandwidth Product Operate Over the -40C to +125C Automotive Temperature Range Tiny 8-Pin MAX Package Ordering Information PART -40C to +125C 8 MAX ADJ MAX4209HAUA+T -40C to +125C 8 MAX 100 Note: All 8-pin MAX packages have package code U8-1. +Denotes a lead(Pb)-free/RoHS-compliant package. Typical Application Circuit 5V R4 VDD/2 IN- R3 IN+ VDD OUT REFIN/MODE Battery-Powered Medical Equipment REF Precision Low-Side Current Sense FB Notebook Computers MAX4208 G = 1 + R2 R1 MAX is a registered trademark of Maxim Integrated Products, Inc. GAIN (V/V) MAX4208AUA+T Industrial Process Control Differential Voltage Amplification PINPACKAGE TEMP RANGE VSS R2 CFB FB R1 REF BUFFER OUT = VDD/2 ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com. 1 MAX4208/MAX4209 General Description MAX4208/MAX4209 Ultra-Low Offset/Drift, Precision Instrumentation Amplifiers with REF Buffer ABSOLUTE MAXIMUM RATINGS VDD to VSS ...............................................................-0.3V to +6V All Other Pins ...................................(VSS - 0.3V) to (VDD + 0.3V) OUT Short-Circuit Duration .......................................Continuous Current Into OUT, VDD, and VSS.......................................25mA Current Into Any Other Pin................................................20mA Continuous Power Dissipation (TA = +70C) 8-Pin MAX (derate 4.5mW/C above +70C) ............362mW Operating Temperature Range .........................-40C to +125C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C 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 = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL = 100k to VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for G = 100V/V (R1 = 1k, R2 = 99k), TA = +25C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX MAX4208, G = 100V/V 3 20 MAX4209H, G = 100V/V 3 20 UNITS INPUT DC CHARACTERISTICS Input Offset Voltage VOS V IB -100mV VDIFF +100mV (Note 3) 1 pA Input Offset Current IOS -100mV VDIFF +100mV (Note 3) 1 pA Input Resistance RIN VCM = VDD/2 Differential mode 2 Common mode 2 Input Bias Current Gain Error Gain Nonlinearity (Note 2) Input Common-Mode Range Input Common-Mode Rejection Ratio 2 VCM CMRR G -20mV VDIFF +20mV MAX4208, G = 100V/V 0.05 0.25 -20mV VDIFF +20mV MAX4209H, G = 100V/V 0.05 0.25 MAX4208, G = 100V/V 25 150 MAX4209H, G = 100V/V 25 150 Guaranteed by CMRR test VCM = (VSS - 0.1V) to (VDD - 1.30V) % VSS 0.1 106 VDD 1.30 135 _______________________________________________________________________________________ ppm V dB Ultra-Low Offset/Drift, Precision Instrumentation Amplifiers with REF Buffer (VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL = 100k to VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for G = 100V/V (R1 = 1k, R2 = 99k), TA = +25C, unless otherwise noted.) (Note 1) PARAMETER Power-Supply Rejection Ratio SYMBOL PSRR CONDITIONS VDD = 2.85V to 5.5V, VREF = VCM = (VSS + 0.5V) MIN TYP 100 125 MAX UNITS dB REFIN/MODE AND REF DC CHARACTERISTICS REFIN/MODE Buffer Input Offset Voltage (Note 2) 10 40 V VSS VSS + 0.05 V REFIN/MODE Input-Voltage Low VIL Reference buffer is OFF REFIN/MODE Input-Voltage High VIH Shutdown mode VDD 0.2 REFIN/MODE Buffered Reference Input Range VREFIN/MODE Reference buffer is ON, guaranteed by REFIN/MODE CMRR test VSS + 0.2 VDD V VDD 1.3 V REFIN/MODE Buffer Common-Mode Rejection Ratio (VSS + 0.2V) VREF/MODE (VDD - 1.3V) (Note 2) 106 135 dB REFIN/MODE Buffer Power-Supply Rejection Ratio VDD = 2.85V to 5.5V, VREF/MODE = VCM = (VSS + 0.5V) 100 125 dB 1 pA REFIN/MODE Bias Current IREFIN VSS < VREFIN/MODE < VDD (Note 3) REF Common-Mode Range Guaranteed by reference CMRR test (Note 4) VSS REF Common-Mode Rejection Ratio VSS VREF (VDD - 1.30V) (Note 4) 106 REF, FB Bias Current REF Input Current (MAX4209) IREF VDD 1.30 V 135 dB MAX4208 (Note 3) 1 pA VDIFF = 0V (Note 5) 10 nA VDIFF = 100mV (Note 5) 100 A OUTPUT DC CHARACTERISTICS RL = 100k VOH VDD - VOUT Output-Voltage Swing (Notes 6 and 7) VOL Short-Circuit Current ISC VOUT - VSS 30 45 RL = 10k 50 70 RL = 1k 250 325 RL = 100k 30 40 RL = 10k 50 65 RL = 1k 250 285 Source +20 Sink -25 Short-Circuit Recovery Time 0.50 mV mA ms AC CHARACTERISTICS Gain-Bandwidth Product GBW MAX4208, G = 1V/V 750 kHz Small-Signal Bandwidth BW MAX4209H, G =100V/V 7.5 kHz Slew Rate (Note 8) SR MAX4208, G = 1V/V, VOUT = 100mV step 80 V/ms _______________________________________________________________________________________ 3 MAX4208/MAX4209 ELECTRICAL CHARACTERISTICS (continued) MAX4208/MAX4209 Ultra-Low Offset/Drift, Precision Instrumentation Amplifiers with REF Buffer ELECTRICAL CHARACTERISTICS (continued) (VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL = 100k to VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for G = 100V/V (R1 = 1k, R2 = 99k), TA = +25C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS Settling Time tS To within 0.1% of final value Maximum Capacitive Load CL No sustained oscillations Input-Voltage Noise en MIN MAX4208, G = 1V/V Shutdown Enable/Disable Time MAX 10 MAX4209H Power-Up Time TYP UNITS s 120 200 pF f = 0.1Hz to 10Hz 2.5 VP-P f = 1kHz 140 nV/Hz To within 0.1% of final value 20 ms 20 ms tEN, tDIS POWER SUPPLY Supply Voltage VDD Supply Current IDD Guaranteed by PSRR test 2.85 5.50 VREFIN/MODE = VSS, buffer OFF VDD = 5V 0.75 1.30 (VSS + 0.2V) VREFIN/MODE (VDD - 1.3V), buffer ON VDD = 5V 1.40 2.30 1.4 5.0 V mA VREFIN/MODE = VDD, shutdown mode A ELECTRICAL CHARACTERISTICS (VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL = 100k to VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for G = 100V/V (R1 = 1k, R2 = 99k), TA = -40C to +125C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS INPUT DC CHARACTERISTICS MAX4208, G = 100V/V Input Offset Voltage VOS MAX4209H, G = 100V/V Input Offset Voltage Temperature Drift (Note 2) Input Bias Current Gain Error MAX4208, G = 100V/V TCVOS MAX4209H, G = 100V/V (Note 3) -100mV VDIFF < +100mV MAX4208, G = 100V/V, -20mV VDIFF +20mV MAX4209H, G = 100V/V, -20mV VDIFF +20mV 4 TA = +25C to +85C 45 TA = -40C to +125C 60 TA = +25C to +85C 30 TA = -40C to +125C V 40 TA = +25C to +85C 0.1 0.45 TA = -40C to +125C 0.1 0.45 TA = +25C to +85C 0.01 0.17 TA = -40C to +125C 0.01 0.17 TA = +85C 10 TA = +125C 20 pA TA = +25C to +85C 0.30 TA = -40C to +125C 0.35 TA = +25C to +85C 0.30 TA = -40C to +125C 0.35 _______________________________________________________________________________________ V/C % Ultra-Low Offset/Drift, Precision Instrumentation Amplifiers with REF Buffer (VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL = 100k to VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for G = 100V/V (R1 = 1k, R2 = 99k), TA = -40C to +125C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL -20mV VDIFF +20mV (MAX4208), G = 100V/V Gain Error Temperature Drift (Note 2) Gain Nonlinearity (Note 2) CONDITIONS Input Common-Mode Rejection Ratio Power-Supply Rejection Ratio TA = -40C to +125C VCM TYP MAX 50 180 TA = -40C to +125C 50 180 MAX4208, G = 100V/V TA = +25C to +85C 210 TA = -40C to +125C 700 MAX4209H, G = 100V/V TA = +25C to +85C 210 TA = -40C to +125C 700 Guaranteed by CMRR test, TA = -40C to +125C CMRR (VSS - 0.1V) VCM (VDD - 1.6V) PSRR VDD = 2.85V to 5.5V, VREF = VCM = VSS + 0.5V UNITS ppm/C -20mV VDIFF +20mV (MAX4209H), G = 100V/V GNL Input Common-Mode Range MIN VSS 0.1 TA = +25C to +85C 96 TA = -40C to +125C 90 TA = +25C to +85C 96 TA = -40C to +125C 90 VDD 1.6 ppm V dB dB REFIN/MODE AND REF DC CHARACTERISTICS REFIN/MODE Buffer Input Offset Voltage REFIN/MODE Buffered Reference Input Range REFIN/MODE Input-Voltage Low VREFIN/MODE VIL TA = +25C to +85C 100 TA = -40C to +125C 100 Reference buffer is ON, guaranteed by REFIN/MODE CMRR test Reference buffer is OFF VSS + 0.2 V VDD 1.6 V VSS + 0.05 V _______________________________________________________________________________________ 5 MAX4208/MAX4209 ELECTRICAL CHARACTERISTICS (continued) MAX4208/MAX4209 Ultra-Low Offset/Drift, Precision Instrumentation Amplifiers with REF Buffer ELECTRICAL CHARACTERISTICS (continued) (VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL = 100k to VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for G = 100V/V (R1 = 1k, R2 = 99k), TA = -40C to +125C, unless otherwise noted.) (Note 1) PARAMETER REFIN/MODE Input-Voltage High SYMBOL VIH CONDITIONS MIN (VSS + 0.2V) VREF (VDD - 1.6V) REF Common-Mode Range (Note 4) Guaranteed by REF CMRR test REF Common-Mode Rejection Ratio VSS VREF (VDD 1.6V) REFIN/MODE Buffer Power-Supply Rejection Ratio VDD = 2.85V to 5.5V, VREFIN/MODE = VCM = (VSS + 0.5V) MAX VDD 0.2 MAX4208/MAX4209 in shutdown REFIN/MODE Buffer Common-Mode Rejection Ratio TYP TA = +25C to +85C 96 TA = -40C to +125C 90 UNITS V dB VSS TA = +25C to +85C 96 TA = -40C to +125C 90 TA = +25C to +85C 96 TA = -40C to +125C 90 VDD 1.6 V dB dB OUTPUT DC CHARACTERISTICS VOH VDD - VOUT Output-Voltage Swing (Note 6) VOL VOUT - VSS RL = 100k 60 RL = 10k 90 RL = 1k 375 RL = 100k 50 RL = 10k 75 RL = 1k 325 mV POWER SUPPLY Supply Voltage Supply Current VDD Guaranteed by PSRR test 2.85 5.50 VREFIN/MODE = VSS, buffer OFF VDD = 5V 1.70 (VSS + 0.2V) VREFIN/MODE (VDD - 1.6V), buffer ON VDD = 5V 3.0 V mA REFIN/MODE = VDD, shutdown mode 10 A Note 1: Specifications are 100% production tested at +25C, unless otherwise noted. Limits over temperature are guaranteed by design. Note 2: Guaranteed by design. Thermocouple and leakage effects preclude measurement of this parameter during production testing. Devices are screened during production testing to eliminate defective units. Note 3: IN+ and IN- are gates to CMOS transistors with typical input bias current of 1pA. CMOS leakage is so small that it is impractical to test and guarantee in production. Max VDIFF is 100mV. Devices are screened during production testing to eliminate defective units. For the MAX4208, when there are no external resistors, the input bias current at FB and REF is 1pA (typ). Note 4: Setting REF to ground (VSS) is allowed if the REF buffer is off. The unity-gain buffer is on when VREFIN/MODE is between 0.15V and (VDD - 1.3V). In this range, VREF = VREFIN/MODE 40V (maximum buffer input offset voltage over temperature). Setting REFIN/MODE to VDD puts the part in shutdown (IDD = 1.4A). Note 5: This is the REF current needed to directly drive the end terminal of the gain-setting resistors when REFIN/MODE is connected to VSS to put the buffer in high-impedance mode. The REF input current is tested at the gain of 100. At gain 10 and 1000, IREF = 100A and 3.4A, respectively at +25C. See the Detailed Description. Note 6: Output swing high (VOH) and output swing low (VOL) are measured only on G = 100 and G = 1000 devices. Devices with G = 1 and G = 10 have output swing high limited by the range of VREF, VCM, and VDIFF (see the Output Swing section). Note 7: Maximum range for VDIFF is from -100mV to +100mV. Note 8: At G = 100V/V and G = 1000V/V, these instrumentation amplifiers are bandwidth limited and not capable of slew-rate-limited dV/dt. 6 _______________________________________________________________________________________ Ultra-Low Offset/Drift, Precision Instrumentation Amplifiers with REF Buffer OFFSET VOLTAGE DRIFT HISTOGRAM (TA = -20C TO +85C) 15 10 15 10 AV = +100V/V 45 40 FREQUENCY (%) 20 FREQUENCY (%) 20 GAIN ACCURACY HISTOGRAM 50 MAX4208/9 toc02 AV = +100V/V 25 FREQUENCY (%) 25 MAX4208/9 toc01 30 MAX4208/9 toc03 INPUT OFFSET VOLTAGE HISTOGRAM 35 30 25 20 15 5 5 10 5 0 0 -20 -15 -10 -5 0 5 10 15 INPUT OFFSET VOLTAGE vs. SUPPLY VOLTAGE INPUT OFFSET VOLTAGE vs. INPUT COMMON-MODE VOLTAGE INPUT OFFSET VOLTAGE vs. REFIN COMMON-MODE (BUFFER ENABLED) TA = -40C 0 -10 TA = -40C 3.0 3.5 4.0 4.5 5.0 5.5 6.0 20 TA = -40C TA = -20C TA = +25C 10 0 -10 -20 TA = +125C TA = +125C TA = +85C -30 -30 2.5 MAX4208/9 toc06 MAX4208/9 toc05 TA = +85C TA = -20C TA = +25C 10 -20 TA = +125C -30 -1 0 1 2 3 0 4 1 2 3 SUPPLY VOLTAGE (V) INPUT COMMON-MODE VOLTAGE (V) REFIN COMMON-MODE (V) LINEARITY ERROR vs. DIFFERENTIAL INPUT VOLTAGE GAIN vs. FREQUENCY COMMON-MODE REJECTION RATIO vs. FREQUENCY 60 0 60 4 MAX4208/9 toc09 AV = +100V/V MAX4208/9 toc08 80 MAX4208/9 toc07 100 -20 -40 40 0 -20 40 CMRR (dB) 20 GAIN (dB) LINEARITY ERROR (ppm) 20 30 INPUT OFFSET VOLTAGE (V) -10 30 INPUT OFFSET VOLTAGE (V) MAX4208/9 toc04 INPUT OFFSET VOLTAGE (V) 0 80 0.05 0.10 0.15 0.20 0.25 GAIN ACCURACY (%) TA = +85C TA = -20C TA = +25C 2.0 0 VOS DRIFT (nV/C) 20 -20 -0.15 -0.10 -0.05 INPUT OFFSET VOLTAGE (V) 30 10 0 -250-200-150-100 -50 0 50 100 150 200 250 300 20 20 -40 -60 -80 -100 -60 0 -120 -80 -100 -140 -20 -30 -20 -10 0 10 20 DIFFERENTIAL INPUT VOLTAGE (mV) 30 10 100 1k 10k 100k FREQUENCY (Hz) 1M 10M 10 100 1k 10k 100k 1M FREQUENCY (Hz) _______________________________________________________________________________________ 7 MAX4208/MAX4209 Typical Operating Characteristics (VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL = 100k to VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for G = 100V/V (R1 = 1k, R2 = 99k), TA = +25C, unless otherwise noted.) Typical Operating Characteristics (continued) (VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL = 100k to VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for G = 100V/V (R1 = 1k, R2 = 99k), TA = +25C, unless otherwise noted.) POWER-SUPPLY REJECTION RATIO vs. FREQUENCY MAX4208 INPUT-REFERRED NOISE MAX4208/9 toc11 MAX4208/9 toc10 0 -20 GAIN (dB) -40 -60 1.2V/div -80 -100 -120 -140 10 100 1k 10k 1s/div 1M 100k FREQUENCY (Hz) 1.2 GREY = OUT OF COMMON-MODE RANGE 0.6 0.3 INTERNAL BUFFER OFF VREFIN/MODE (VSS + 0.05V) CFB = 10nF CAPACITOR 100 1k 10k 2.5 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 3.0 3.5 SHUTDOWN CURRENT vs. SUPPLY VOLTAGE SUPPLY CURRENT (BUFFER ON) vs. SUPPLY VOLTAGE 6.0 MAX4208/9 toc15 VREFIN/MODE = VDD/2 VREFIN/MODE = VDD 5.0 1.5 IDD (A) IDD (mA) 4.0 1.0 TA = +125C 3.0 TA = +25C TA = -40C TA = +25C TA = +125C 2.0 0.5 1.0 2.5 3.0 3.5 4.0 VDD (V) 8 TA = -40C 0 0 4.5 5.0 5.5 4.0 VDD (V) VREFIN/MODE (V) FREQUENCY (Hz) 2.0 TA = +25C 400 0 100k MAX4208/9 toc16 10 TA = -40C 500 0 1 700 600 SHUTDOWN MODE 10 TA = +125C 800 0.9 IDD (A) IDD (mA) 100 VREFIN/MODE = VSS 900 INTERNAL BUFFER ON VREFIN/MODE (VSS + 0.2V) CFB = 1nF CAPACITOR MAX4208/9 toc14 1000 MAX4208/9 toc13 WHITE NOISE 140nV/Hz 1000 1.5 MAX4208/9 toc12 10,000 SUPPLY CURRENT (BUFFER OFF) vs. SUPPLY VOLTAGE IDD vs. VREFIN/MODE INPUT NOISE vs. FREQUENCY INPUT-NOISE DENSITY (nV/Hz) MAX4208/MAX4209 Ultra-Low Offset/Drift, Precision Instrumentation Amplifiers with REF Buffer 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VDD (V) _______________________________________________________________________________________ 4.5 5.0 5.5 Ultra-Low Offset/Drift, Precision Instrumentation Amplifiers with REF Buffer LARGE-SIGNAL PULSE RESPONSE TIME LARGE-SIGNAL PULSE RESPONSE TIME MAX4208/9 toc17 MAX4208/9 toc18 VIN+ 5mV/div 2.5V VIN+ 5mV/div 2.5V OUTPUT 50mV/div 2.5V OUTPUT 500mV/div 2.5V 100s/div AV = 10V/V VIN+ = 10mV STEP VIN- = VREF = (VDD - VSS)/2 VREFIN/MODE = VSS 400s/div AV = 100V/V VIN+ = 10mV STEP VIN- = VREF = (VDD - VSS)/2 VREFIN/MODE = VSS LARGE-SIGNAL PULSE RESPONSE TIME MAX4208/9 toc19 VIN+ 1mV/div 2.5V OUTPUT 1V/div 2.5V 400s/div AV = 1000V/V VIN+ = 2mV STEP VIN- = VREF = (VDD - VSS)/2 VREFIN/MODE = VSS _______________________________________________________________________________________ 9 MAX4208/MAX4209 Typical Operating Characteristics (continued) (VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL = 100k to VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for G = 100V/V (R1 = 1k, R2 = 99k), TA = +25C, unless otherwise noted.) Typical Operating Characteristics (continued) (VDD = 5V, VSS = 0V, VCM = VREF = VDD/2, VREFIN/MODE = VSS, RL = 100k to VDD/2, VDIFF = (VIN+ - VIN-) = 0V, MAX4208 set for G = 100V/V (R1 = 1k, R2 = 99k), TA = +25C, unless otherwise noted.) 0.1% SETTLING TIME vs. GAIN 180 G = 100 160 SETTLING TIME (s) 140 1000 100 MAX4208/9 toc22 SETTLING TIME vs. ACCURACY MAX4208/9 toc21 10,000 SETTLING TIME (s) MAX4208/MAX4209 Ultra-Low Offset/Drift, Precision Instrumentation Amplifiers with REF Buffer 120 100 80 60 40 20 10 0 1 10 100 GAIN (V/V) 1000 0.10 0.01 1.00 ACCURACY (%) Pin Description PIN 1 2 10 NAME FUNCTION Reference/Shutdown Mode Input. Trimode function is as follows: Connect to VDD to put the device in shutdown mode. Connect to an external reference (between VSS + 0.2V and VDD - 1.3V) to buffer the voltage at REFIN/MODE REFIN/MODE. Using the REF buffer allows the use of a simple resistor-divider or high-impedance external reference to set the OUT level at 0mV IN with minimum error. Connect to VSS to force the internal buffer output into a high-impedance state to allow external direct drive of REF. INNegative Differential Input 3 IN+ Positive Differential Input 4 VSS Negative Supply Input. Bypass VSS to ground with a 0.1F capacitor or connect to ground for single-supply operation. 5 REF Output Reference Level. REF sets the OUT voltage for zero differential input. The internal buffer sets the voltage at REF when the voltage at REFIN/MODE is between VSS + 0.2V and VDD - 1.3V. 6 FB 7 OUT Amplifier Output 8 VDD Positive Supply Input. Bypass VDD to ground with a 0.1F capacitor. Feedback Input. Connect FB to the center tap of an external resistive divider from OUT to REF to set the gain for the MAX4208. MAX4209 FB is internally connected to gain-setting resistors. Connect an optional capacitor, CFB, from OUT to FB to reduce autozero noise. ______________________________________________________________________________________ Ultra-Low Offset/Drift, Precision Instrumentation Amplifiers with REF Buffer VDD MAX4208 MAX4209 OUT AMP OUT AMP R2 FB INgm R2 IN- FB R1 gm IN+ REF +1 gm gm REF REFIN/MODE VSS Figure 1. MAX4208 Functional Diagram Detailed Description The MAX4208/MAX4209 family of instrumentation amplifiers implements a spread-spectrum, autozeroing technique that minimizes the input offset error, drift over time and temperature, and the effect of 1/f noise. Unlike the traditional three-op amp instrumentation amplifier, this technique allows true ground-sensing capability combined with a low input bias current and increased common-mode rejection. The differential input signal is converted to a current by an input transconductance stage. An output transconductance stage converts a portion of the output voltage (equal to the output voltage divided by the gain) into another precision current. These two currents are subtracted and the result is fed to a loop amplifier with sufficient gain to minimize errors (Figures 1 and 2). The MAX4209 has a factory-trimmed gain of 100V/V. The MAX4208 has an adjustable gain, set with an external pair of resistors between OUT, FB, and REF (Figure 1). The MAX4208/MAX4209 have an output reference input (REF) that is connected to an external reference for bipolar operation of the device. For single-supply operation, the range for VREF is 0V to (VDD - 1.3V). Although full output-swing capability and maximum symmetrical dynamic range is obtained at REF = VDD/2, the optimal VREF setting depends on the supply voltage and output-voltage R1 IN+ +1 SHDN G = 1 + R2 R1 MAX4208/MAX4209 VDD REFIN/MODE SHDN G = 1 + R2 R1 VSS Figure 2. MAX4209 Functional Diagram swing needed by the application. The maximum recommended differential input voltage is 100mV. Linearity and accuracy are degraded above that level. The MAX4208/MAX4209 operate with single 2.85V to 5.5V supply voltages or dual 1.425V to 2.75V supplies. The MAX4208/MAX4209 have a shutdown feature to reduce the supply current to 1.4A (typ) when REFIN/ MODE is connected to VDD. REF, REFIN/MODE, and Internal REFIN Buffer of the MAX4208/MAX4209 In a single-supply system, bipolar operation of an instrumentation amplifier requires the application of a voltage reference (REF) to set the output voltage level when a zero differential voltage is applied to the input. The output swing is around this reference level, which is usually set to half of the supply voltage for the largest swing and dynamic range. In many instrumentation amplifiers, the gain-setting resistors as well as the RL are connected between OUT and REF. OUT can sink and source current but the need for REF to sink and source current is often overlooked and can lead to significant errors. Therefore, the MAX4208/MAX4209 include a REFIN buffer, an internal, precision unity-gain buffer on-chip to sink and source the currents needed at REF without loading the reference voltage supplied at REFIN/MODE. ______________________________________________________________________________________ 11 MAX4208/MAX4209 Ultra-Low Offset/Drift, Precision Instrumentation Amplifiers with REF Buffer Table 1. REFIN/MODE Pin Functions REFIN/MODE VOLTAGE* VDD (typically +5V) STATE OF MAX4208/MAX4209 and REFIN BUFFER The entire IC is in SHDN mode and draws 1.4A of supply current. Between VSS + 200mV and (VDD - 1.3V) The internal REF buffer is activated. REF MUST NOT be fed by any external source. The voltage at REFIN/MODE is transferred to REF within 40V, max (VOS of the internal REF buffer). VSS (typically ground) The internal REF buffer is OFF with its output in a high-impedance state to allow direct drive of REF (or connection to ground). REF must be directly connected to an external voltage reference capable of sinking and sourcing the load current. *See the Electrical Characteristics table for detailed specifications. In a conventional instrumentation amplifier, a simple method to apply a reference voltage is the use of a voltage-divider to set the REF level (often halfway between ground and VDD). The voltage-divider should be made of higher value resistors to minimize current consumption, but the sinking and sourcing current from the load and gain-setting resistors create a significant commonmode signal at the divider midpoint. The MAX4208/ MAX4209 precision REFIN buffer essentially eliminates the error voltage at REF. The REFIN buffer is a unity-gain op amp that has a guaranteed VOS of less than 40V with a CMOS input bias current of only 1pA, to allow setting REFIN with a simple resistive divider with minimum errors. REFIN/MODE is a triple function input (see Table 1). To use the internal REFIN buffer, connect REFIN/MODE to an external reference or a simple resistive divider at any voltage between (VSS + 0.2V) and (VDD - 1.3V). These voltages represent the minimum and maximum for the REFIN buffer's input common-mode range (see the Electrical Characteristics table). To use ground at REF or to use an external low-impedance reference directly at REF without the internal REFIN buffer, connect REFIN/MODE to V SS . This disables the REFIN buffer, dropping the IDD to 750A and puts the REFIN buffer output in a high-impedance state to allow external direct drive of REF. To put the MAX4208/MAX4209 into shutdown and reduce the supply current to less than 5A, drive REFIN/MODE to VDD. Note: When driving REF directly, REFIN/MODE must be at VSS and shutdown mode is NOT available. Input Differential Signal Range The MAX4208/MAX4209 feature a proprietary input structure optimized for small differential signals of up to 100mV. The output of the MAX4208/MAX4209 allows for bipolar input signals. The output voltage is equal to the voltage at REF for zero differential input. The gain accuracy of these devices is laser trimmed to better than 0.1% (typ). 12 Output Swing The MAX4208/MAX4209 are designed specifically for small input signals (100mV) from sensors, strain gauges, etc. These instrumentation amplifiers are capable of rail-to-rail output-voltage swings; however, depending on the selected gain and REF level, the railto-rail output swing may not be required or desired. For example, consider single-supply operation of the MAX4208 in a unity-gain configuration with REF connected to a voltage at half of the supply voltage (VDD / 2). In this case, the output-voltage swing would be 100mV around the REF level and would not need to reach either rail. Another example is the MAX4209H (gain internally set to 100) also operating with a single-supply voltage and REF set externally to ground (VSS). REFIN/MODE must also be connected to ground (VSS). In this case, an input voltage of 0 to 10mV differential would ideally drive an output-voltage swing of 0 to 1V. However, the output swing can only get to within 40mV of ground (V SS ) (see the V OL specifications in the Electrical Characteristics table). It is recommended that for best accuracy and linearity, the lowest differential input voltage for unipolar operation is usually picked to be a nonzero value (e.g., 0.5mV or more). Another remedy is to use REFIN/MODE of 250mV (see the REFIN/MODE Buffered Reference Input Range in the Electrical Characteristics table), which causes a 0 to 100mV input to start OUT at 250mV and swing to 1.25V, to prevent the output from going into its bottom nonlinear range. An ADC with differential input can be connected between OUT and REF to record the true 0 to 1V swing. Devices with higher gain and bipolar output swing can be configured to approach either rail for maximum dynamic range. However, as the output approaches within VOL or VOH of the supply voltages, the linearity and accuracy degrades, especially under heavy loading. ______________________________________________________________________________________ Ultra-Low Offset/Drift, Precision Instrumentation Amplifiers with REF Buffer Setting the Gain (MAX4208) Connect a resistive divider from OUT to REF with the center tap connected to FB to set the gain for the MAX4208 (see the Typical Application Circuit). Calculate the gain using the following formula: R2 GAIN = 1 + R1 Choose a value for R1 1k. Resistor accuracy ratio directly affects gain accuracy. Resistor sum less than 10k should not be used because their loading can slightly affect output accuracy. Input Common Mode vs. Input Differential-Voltage Range Traditional three-op amp instrumentation amplifiers have a defined relationship between the maximum input differential voltage and maximum input commonmode voltage that arises from saturation of intermediate amplifier stages. This correlation is frequently represented as a hexagon graph of input common-mode voltage vs. output voltage for the instrumentation amplifier shown in Figure 3. Application limitations hidden in this graph are: * The input common-mode voltage range does not include the negative supply rail, and so no amplification is possible for inputs near ground for singlesupply applications. * Input differential voltages can be amplified with maximum gain only over a limited range of input common-mode voltages (i.e., range of y-axis for max range of x-axis is limited). * If large amplitude common-mode voltages need to be rejected, differential voltages cannot be amplified with a maximum gain possible (i.e., range of x-axis for a maximum range of y-axis is limited). As a consequence, a secondary high-gain amplifier is required to follow the front-end instrumentation amplifier. The indirect current-feedback architecture of the MAX4208/MAX4209 instrumentation amplifiers do not suffer from any of these drawbacks. Figure 4 shows the input common-mode voltage vs. output voltage graph of indirect current-feedback architecture. In contrast to three-op amp instrumentation amplifiers, the MAX4208/MAX4209 features: * The input common-mode voltage range, which includes the negative supply rail and is ideal for single-supply applications. * Input differential voltages that can be amplified with maximum gain over the entire range of input common-mode voltages. * Large common-mode voltages that can be rejected at the same time differential voltages are amplified with maximum gain, and therefore, no secondary amplifier is required to follow the front-end instrumentation amplifier. Gain Error Drift Over Temperature Adjustable gain instrumentation amplifiers typically use a single external resistor to set the gain. However, due to differences in temperature drift characteristics between the internal and external resistors, this leads to large gain-accuracy drift over temperature. The MAX4208 is an adjustable gain instrumentation amplifier that uses two external resistors to set its gain. Since both resistors are external to the device, layout and temperature coefficient matching of these parts deliver a significantly more stable gain over operating temperatures. The fixed gain, MAX4209H has both internal resistors for excellent matching and tracking. Use of External Capacitor CFB for Noise Reduction Zero-drift chopper amplifiers include circuitry that continuously compensates the input offset voltage to deliver precision and ultra-low temperature drift characteristics. This self-correction circuitry causes a small additional noise contribution at its operating frequency (a psuedorandom clock around 45kHz for MAX4208/MAX4209). For high-bit resolution ADCs, external filtering can significantly attenuate this additional noise. Simply adding a feedback capacitor (C FB ) between OUT and FB reduces high-frequency gain, while retaining the excellent precision DC characteristics. Recommended values for CFB are between 1nF and 10nF. Additional anti-aliasing filtering at the output can further reduce this autocorrection noise. Capacitive-Load Stability The MAX4208/MAX4209 are capable of driving capacitive loads up to 200pF. Applications needing higher capacitive drive capability may use an isolation resistor between OUT and the load to reduce ringing on the output signal. However, this reduces the gain accuracy due to the voltage drop across the isolation resistor. ______________________________________________________________________________________ 13 MAX4208/MAX4209 Applications Information MAX4208/MAX4209 Ultra-Low Offset/Drift, Precision Instrumentation Amplifiers with REF Buffer VCM CLASSIC THREE OP-AMP INA VCM VCC VDD VCM-MAX VCM-MAX MAX4208/MAX4209 3/4 VCC 1/2 VCC VREF = 1/2 VCC VREF = 1/2 VDD 1/4 VCC VOUT ( = GAIN x VDIFF + VREF) VOUT ( = GAIN x VDIFF + VREF) 0 VCC/2 0 VCC Figure 3. Limited Common Mode vs. Output Voltage of a Three Op-Amp INA VDD/2 VDD Figure 4. Input Common Mode vs. Output Voltage of MAX4208/MAX4209 Includes 0V (GND) Power-Supply Bypass and Layout Low-Side Current-Sense Amplifier Good layout technique optimizes performance by decreasing the amount of stray capacitance at the instrumentation amplifier's gain-setting pins (OUT, FB, and REF). Excess capacitance produces peaking in the amplifier's frequency response. To decrease stray capacitance, minimize trace lengths by placing external components as close as possible to the instrumentation amplifier. Unshielded long traces at the inputs of the instrumentation amplifier degrade the CMRR and pick-up noise. This produces inaccurate output in highgain configurations. Use shielded or coax cables to connect the inputs of the instrumentation amplifier. Since the MAX4208/MAX4209 feature ultra-low input offset voltage, board leakage and thermocouple effects can easily introduce errors in the input offset voltage readings when used with high-impedance signal sources. Minimize board leakage current and thermocouple effects by thoroughly cleaning the board and placing the matching components very close to each other and with appropriate orientation. For best performance, bypass each power supply to ground with a separate 0.1F capacitor. For noisy digital environments, the use of multilayer PCB with separate ground and power-supply planes is recommended. Keep digital signals far away from the sensitive analog inputs. Refer to the MAX4208 or MAX4209 Evaluation Kit data sheets for good layout examples. The use of indirect current-feedback architecture makes the MAX4208/MAX4209 ideal for low-side current-sensing applications, i.e., where the current in the circuit ground needs to be measured by means of a small sense resistor. In these situations, the input common-mode voltage is allowed to be at or even slightly below ground (VSS - 0.1V). If the currents to be measured are bidirectional, connect REFIN/MODE to VDD/2 to get full dynamic range for each direction. If the currents to be measured are unidirectional, both REFIN/MODE and REF can be tied to GND. However, VOL limitations can limit low-current measurement. If currents need to be measured down to 0A, bias REFIN/MODE to a voltage above 0.2V to activate the internal buffer and to stay above amplifier VOL, and measure both OUT and REF with a differential input ADC. 14 Low-Voltage, High-Side Current-Sense Amplifier Power management is a critical area in high-performance portable devices such as notebook computers. Modern digital processors and ASICs are using smaller transistor geometries to increase speed, reduce size, and also lower their operating core voltages (typically 0.9V to 1.25V). The MAX4208/MAX4209 instrumentation amplifiers can be used as a nearly zero voltage-drop, current-sense amplifier (see Figure 5). ______________________________________________________________________________________ Ultra-Low Offset/Drift, Precision Instrumentation Amplifiers with REF Buffer VSENSE = 10A x 0.002 = 20mV POWER IN RSENSE = 10A x 20mV = 200mW OUT = G x 20mV = 100 x 20mV = 2V MAX4209H gain error is 0.25% max at 100x, so the total accuracy is greatly improved. The 0 to 2V output of MAX4209H can be sent to an ADC for calculation. The adjustable gain of MAX4208, can be set to a gain of 250x using 1k and 249k resistors, to scale up a lower 10mV VSENSE voltage to a larger 2.5V output voltage for wider dynamic range as needed. +3.3V MAX4209H IN+ VDD IN- VSS REF 1V AT 10A OUT ADC REFIN/MODE 0.002 +VSENSE- ANTI-ALIASING FILTER ASIC Figure 5. MAX4208/MAX4209 Used as Precision Current-Sense Amplifiers for Notebook Computers with VSENSE of 20mV Typical Application Circuit 5V R4 VDD/2 IN- R3 IN+ VDD OUT REFIN/MODE REF VSS R2 CFB FB MAX4208 G = 1 + R2 R1 FB R1 REF BUFFER OUT = VDD/2 ______________________________________________________________________________________ 15 MAX4208/MAX4209 The ultra-low VOS of the MAX4208/MAX4209 allows fullscale VSENSE of only 10mV to 20mV for minimally invasive current sensing using milliohm sense resistors to get high accuracy. Previous methods used the internal resistance of the inductor in the step-down DC-DC converter to measure the current, but the accuracy was only 20% to 30%. Using a full-scale VSENSE of 20mV, a 20V max, V OS error term is less than 0.1% and Ultra-Low Offset/Drift, Precision Instrumentation Amplifiers with REF Buffer MAX4208/MAX4209 Pin Configuration TOP VIEW + REFIN/MODE 1 ININ+ 2 3 MAX4208 MAX4209 VSS 4 8 VDD 7 OUT 6 FB 5 REF MAX Package Information Chip Information TRANSISTOR COUNT: 2335 PROCESS: BiCMOS For the latest package outline information, go to www.maxim-ic.com/package. PACKAGE TYPE 8 MAX 16 PACKAGE CODE DOCUMENT NO. U8-1 21-0036 ______________________________________________________________________________________ Ultra-Low Offset/Drift, Precision Instrumentation Amplifiers with REF Buffer REVISION NUMBER REVISION DATE 0 9/07 Initial release 1 4/09 Removed future products DESCRIPTION PAGES CHANGED -- 1-5, 11, 12, 13 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. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 17 (c) 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc. MAX4208/MAX4209 Revision History