EVALUATION KIT AVAILABLE MAX44250/MAX44251/MAX44252 20V, Ultra-Precision, Low-Noise Op Amps General Description The MAX44250/MAX44251/MAX44252 are 20V, ultraprecision, low-noise, low-drift amplifiers that offer nearzero DC offset and drift through the use of patented autocorrelating zeroing techniques. This method constantly measures and compensates the input offset, eliminating drift over time and temperature and the effect of 1/f noise. These single, dual, and quad devices feature rail-to-rail outputs, operate from a single 2.7V to 20V supply or dual ±1.35V to ±10V supplies and consume only 1.15mA per channel, while providing 5.9nV/√Hz input-referred voltage noise. The ICs are unity-gain stable with a gainbandwidth product of 10MHz. With excellent specifications such as offset voltage of 6µV (max), drift of 19nV/°C (max), and 123nVP-P noise in 0.1Hz to 10Hz, the ICs are ideally suited for applications requiring ultra-low noise and DC precision such as interfacing with pressure sensors, strain gauges, precision weight scales, and medical instrumentation. Benefits and Features S 2.7V to 20V Power-Supply Range S Integrated EMI Filter S 6µV Input Offset Voltage (max) at Room Temperature S TCVOS of 19nV/°C (max) S Low 5.9nV/√Hz Input-Referred Voltage Noise S 123nVP-P in 0.1Hz to 10Hz S Fast 400ns Settling Time S 10MHz Gain-Bandwidth Product S Rail-to-Rail Output S High Accuracy Enables Precision Signal Chain Acquisition Applications Strain Gauges Pressure Transducers Medical Instrumentation Precision Instrumentation Load Cell and Bridge Transducer Amplification The ICs are available in 5-pin SOT23, 8-pin SOT23, 8-pin µMAXM, and 14-pin SO packages and are rated over the -40°C to +125°C temperature range. Ordering Information appears at end of data sheet. For related parts and recommended products to use with this part, refer to www.maximintegated.com/MAX44250.related. Functional Diagrams appear at end of data sheet. Typical Operating Circuit 3.3V +10V 3V MAX44251 R BUFFER R1 10V -10V RG 50RG 50RG MAX44251 VDD BUFFER VDD VREF VIN+ R MICROPROCESSOR MAX11211OUTPUT +10V R MAX44251 MAX6126 +10V R BUFFER VOUT -10V 1.5V VIN- VSS C1 -10V µMAX is a registered trademark of Maxim Integrated Products, Inc. For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com. 19-6000; Rev 3; 4/13 MAX44250/MAX44251/MAX44252 20V, Ultra-Precision, Low-Noise Op Amps Absolute Maximum Ratings Supply Voltage (VDD to VSS).................................-0.3V to +22V All Other Pins...................................(VSS - 0.3V) to (VDD + 0.3V) Short-Circuit Duration to Either Supply Rail............................. 1s Continuous Input Current (any pin).................................. ±20mA Differential Input Voltage....................................................... ±6V Maximum Power Dissipation (TA = +70°C) 5-Pin SOT23 (derate 3.1mW/°C above +70°C).........246.7mW 8-Pin SOT23 (derate 9.1mW/°C above +70°C)............727mW µMAX (derate 4.5 mW/°C above +70°C).....................362mW SO (derate 8.3 mW/°C above +70°C).......................666.7mW Operating Temperature Range......................... -40°C to +125NC Junction Temperature......................................................+150NC Storage Temperature Range............................. -65°C to +150NC Lead Temperature (soldering, 10s)............................... +300NC Soldering Temperature (reflow)..................................... +260NC 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. Package Thermal Characteristics (Note 1) 5-Pin SOT23 Junction-to-Ambient Thermal Resistance (ΘJA)..... 324.3°C/W Junction-to-Case Thermal Resistance (ΘJC)................82°C/W 8-Pin SOT23 Junction-to-Ambient Thermal Resistance (ΘJA)........ 196°C/W Junction-to-Case Thermal Resistance (ΘJC)................70°C/W µMAX Junction-to-Ambient Thermal Resistance (ΘJA).........221°C/W Junction-to-Case Thermal Resistance (ΘJC)................42°C/W SO Junction-to-Ambient Thermal Resistance (ΘJA).........120°C/W Junction-to-Case Thermal Resistance (ΘJC)................37°C/W Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer board. For detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial. Electrical Characteristics (VDD = 10V, VSS = 0V, VIN+ = VIN- = VDD/2, RL = 10kI to VDD/2, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 20 V POWER SUPPLY Supply Voltage Range Power-Supply Rejection Ratio (Note 3) VDD PSRR Guaranteed by PSRR 2.7 VDD = 2.7V to 20V, VCM = 0V 140 Quiescent Current per Amplifier (MAX44250) IDD RL = J Quiescent Current per Amplifier (MAX44251/MAX44252) IDD RL = J Power-Up Time tON 145 1.22 TA = +25NC dB 1.7 1.85 -40NC < TA < +125NC 1.15 TA = +25NC 1.55 1.75 -40NC < TA < +125NC 25 mA mA Fs DC SPECIFICATIONS Input Common-Mode Range Common-Mode Rejection Ratio (Note 3) Input Offset Voltage (MAX44250) (Note 3) Maxim Integrated VCM CMRR VOS Guaranteed by CMRR test VSS 0.05 TA = +25NC, VCM = -0.05V to (VDD 1.5V) 133 -40NC < TA < +125NC 130 TA = +25NC VDD 1.5 140 3 V dB 9 FV 2 MAX44250/MAX44251/MAX44252 20V, Ultra-Precision, Low-Noise Op Amps ELECTRICAL CHARACTERISTICS (continued) (VDD = 10V, VSS = 0V, VIN+ = VIN- = VDD/2, RL = 10kI to VDD/2, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2) PARAMETER Input Offset Voltage (MAX44251/ MAX44252)(Note 3) SYMBOL VOS CONDITIONS MIN TA = +25NC TYP MAX 3 6 7 -40NC < TA < +125NC UNITS FV Input Offset Voltage Drift (MAX44250) (Note 3) TC VOS 5 26 nV/NC Input Offset Voltage Drift (MAX44251/MAX44252)(Note 3) TC VOS 5 19 nV/NC Input Bias Current (MAX44250) (Note 3) IB TA = +25NC 200 1400 pA Input Bias Current (MAX44251/ MAX44252)(Note 3) IB TA = +25NC 200 1300 Input Offset Current (Note 3) Open-Loop Gain (Note 3) 2400 -40NC < TA < +125NC IOS AVOL Output Short-Circuit Current 400 250mV P VOUT P VDD - 250mV, RL = 10kI to VDD/2 To VDD or VSS Output Voltage Low (MAX44250) VOL VOUT - VSS Output Voltage Low (MAX44251/MAX44252) VOL VOUT - VSS Output Voltage High (MAX44250) VOH VDD - VOUT Output Voltage High (MAX44251/MAX44252) VOH VDD - VOUT TA = +25NC 145 -40NC < TA < +125NC 136 pA pA 154 dB Noncontinuous 96 mA RL = 10kI to VDD/2 12 26 RL = 2kI to VDD/2 45 92 RL = 10kI to VDD/2 12 25 RL = 2kI to VDD/2 45 85 RL = 10kI to VDD/2 18 40 RL = 2kI to VDD/2 71 148 RL = 10kI to VDD/2 18 37 RL = 2kI to VDD/2 71 135 mV mV mV mV AC SPECIFICATIONS Input Voltage-Noise Density eN Input Voltage Noise Input Current-Noise Density Input Capacitance Gain-Bandwidth Product iN f = 1kHz 5.9 0.1Hz < f < 10Hz 123 nVP-P f = 1kHz 0.6 pA/√Hz CIN 2 pF GBW 10 MHz 60 Degrees 8 V/Fs 500 pF Phase Margin PM CL = 20pF Slew Rate SR AV = 1V/V, VOUT = 2VP-P Capacitive Loading CL No sustained oscillation, AV = 1V/V VOUT = 2VP-P, f = 1kHz AV = +1V/V, RL = 10kI to f = 20kHz VDD/2 To 0.01%, VOUT = 2V step, AV = -1V/V Total Harmonic Distortion Settling Time Maxim Integrated nV/√Hz THD -124 -119 400 dB ns 3 MAX44250/MAX44251/MAX44252 20V, Ultra-Precision, Low-Noise Op Amps ELECTRICAL CHARACTERISTICS (VDD = 3.3V, VSS = 0V, VIN+ = VIN- = VDD/2, RL = 10kI to VDD/2, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX 1.17 1.65 UNITS POWER SUPPLY Quiescent Current Per Amplifier (MAX44250) IDD RL = J Quiescent Current Per Amplifier (MAX44251/MAX44252)) IDD RL = J Power-Up Time tON TA = +25NC -40NC < TA < +125NC 1.80 TA = +25NC 1.1 -40NC < TA < +125NC 1.5 1.65 25 mA mA Fs DC SPECIFICATIONS Input Common-Mode Range Common-Mode Rejection Ratio (Note 3) VCM CMRR Input Offset Voltage (MAX44250)(Note 3) VOS Input Offset Voltage (MAX44251/ MAX44252)(Note 3) VOS Guaranteed by CMRR test VSS 0.05 TA = +25NC, VCM = -0.05V to (VDD 1.5V) 120 -40NC < TA < +125NC 117 TA = +25NC VDD 1.5 129 dB 3 8.5 3 5.5 -40NC < TA < +125NC V 6.5 FV FV Input Offset Voltage Drift (MAX44250)(Note 3) TC VOS 8 25 nV/NC Input Offset Voltage Drift (MAX44251/MAX44252)(Note 3) TC VOS 8 18 nV/NC Input Bias Current (MAX44250)(Note 3) IB 200 1450 pA Input Bias Current (MAX44251/ MAX44252)(Note 3) IB 200 1100 Input Offset Current (Note 3) IOS Open-Loop Gain (Note 3) AVOL Output Short-Circuit Current TA = +25NC -40NC < TA < +125NC 400 250mV P VOUT P VDD - 250mV, RL = 10kI to VDD/2 TA = +25NC 136 -40NC < TA < +125NC 133 To VDD or VSS Noncontinuous Output Voltage Low (MAX44250) VOL VOUT - VSS Output Voltage Low (MAX44251/MAX44252) VOL VOUT - VSS Output Voltage High VOH VDD - VOUT Maxim Integrated 1200 pA pA 151 dB 58 mA RL = 10kI to VDD/2 5 26 RL = 2kI to VDD/2 17 46 RL = 10kI to VDD/2 5 22 RL = 2kI to VDD/2 17 42 RL = 10kI to VDD/2 9 22 RL = 2kI to VDD/2 29 52 mV mV mV 4 MAX44250/MAX44251/MAX44252 20V, Ultra-Precision, Low-Noise Op Amps ELECTRICAL CHARACTERISTICS (continued) (VDD = 3.3V, VSS = 0V, VIN+ = VIN- = VDD/2, RL = 10kI to VDD/2, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS AC SPECIFICATIONS Input Voltage-Noise Density eN Input Voltage Noise Input Current-Noise Density Input Capacitance Gain-Bandwidth Product iN f = 1kHz 6.2 nV/√Hz 0.1Hz < f < 10Hz 123 nVP-P f = 1kHz 0.3 pA/√Hz CIN 2 pF GBW 10 MHz Phase Margin PM CL = 20pF 60 Degrees Slew Rate SR AV = 1V/V, VOUT = 1VP-P, 10% to 90% 5 V/Fs Capacitive Loading CL No sustained oscillation, AV = 1V/V 500 pF Total Harmonic Distortion VOUT = 1VP-P, AV = +1V/V, VCM = VDD/4, RL = 10kI to VDD/2 THD f = 1kHz -124 dB f = 20kHz -100 To 0.01%, VOUT = 1V step, AV = -1V/V Settling Time 200 ns Note 2: All devices are 100% production tested at TA = +25°C. Temperature limits are guaranteed by design. Note 3: Guaranteed by design. Typical Operating Characteristics (VDD = 10V, VSS = 0V, outputs have RL = 10kI to VDD/2. TA = +25NC, unless otherwise specified.) INPUT OFFSET VOLTAGE DRIFT HISTOGRAM SUPPLY CURRENT (mA) 35 30 25 20 15 10 Maxim Integrated TA = +85°C 1.0 TA = +25°C TA = 0°C TA = -40°C 0.8 0.6 0.4 SUPPLY CURRENT PER AMPLIFIER 0.2 0 OFFSET VOLTAGE (µV) TA = +125°C 1.2 MAX44250 toc03 40 5 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY CURRENT vs. SUPPLY VOLTAGE 1.4 MAX44250 toc02 45 PERCENT OCCURRENCE (%) MAX44250 toc01 PERCENT OCCURRENCE (%) OFFSET VOLTAGE HISTOGRAM 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 0 -0.001 0 0.001 0.002 0.003 0.004 0.005 0.006 OFFSET VOLTAGE DRIFT (µV/°C) 0 5 10 15 20 25 SUPPLY VOLTAGE (V) 5 MAX44250/MAX44251/MAX44252 20V, Ultra-Precision, Low-Noise Op Amps Typical Operating Characteristics (continued) (VDD = 10V, VSS = 0V, outputs have RL = 10kI to VDD/2. TA = +25NC, unless otherwise specified.) INPUT OFFSET VOLTAGE vs. INPUT COMMON MODE 1.24 5 1.22 5 VOS (µV) 1.18 1.16 1.14 1.12 SUPPLY CURRENT PER AMPLIFIER 1.08 4 VOS (µV) 4 1.20 1.10 3 2 1 1 -25 0 25 50 75 100 125 150 2 4 6 8 10 -25 0 25 50 75 100 INPUT COMMON VOLTAGE (V) TEMPERATURE (°C) INPUT BIAS CURRENT vs. COMMON-MODE VOLTAGE INPUT BIAS CURRENT vs. TEMPERATURE COMMON-MODE REJECTION RATIO vs. FREQUENCY TA = +25°C 500 0 -500 -250 -1500 0 -20 -1250 -2 -1 0 1 2 3 INPUT COMMON-MODE VOLTAGE (V) Maxim Integrated 4 60 20 -1000 IBIAS+ 80 40 NEGATIVE IBIAS -750 -1000 -3 120 100 0 -500 -4 140 250 IBIAS (pA) 1000 POSITIVE IBIAS 500 160 CMRR (dB) TA = -40°C 750 125 MAX44250 toc09 1000 MAX44250 toc07 TA = +125°C IBIAS- -5 -50 TEMPERATURE (°C) 2000 1500 0 0 MAX44250 toc08 -50 3 2 0 1.06 INPUT BIAS CURRENT (pA) 6 MAX44250 toc05 1.26 SUPPLY CURRENT (mA) 6 MAX44250 toc04 1.28 INPUT OFFSET VOLTAGE vs. TEMPERATURE MAX44250 toc06 SUPPLY CURRENT vs. TEMPERATURE -50 -25 0 25 50 75 TEMPERATURE (°C) 100 125 150 0.1 1 10 100 1k 10k 100k 1M 10M 100M FREQUENCY (Hz) 6 MAX44250/MAX44251/MAX44252 20V, Ultra-Precision, Low-Noise Op Amps Typical Operating Characteristics (continued) (VDD = 10V, VSS = 0V, outputs have RL = 10kI to VDD/2. TA = +25NC, unless otherwise specified.) 400 300 200 250 25 200 150 100 20 15 10 100 50 5 0 0 0 6 8 10 0 2 OUTPUT VOLTAGE SWING LOW vs. TEMPERATURE 12 10 8 6 4 2 -50 10 140 120 0 25 50 75 100 80 60 40 20 0 1 15 10 5 INPUT CURRENT NOISE vs. FREQUENCY MAX44250 toc17 5 4 0 -2 MAGNITUDE (dB) INPUT CURRENT NOISE (pA/√Hz) 2 10k 100k 3 2 -4 -6 -8 -10 -12 -14 1 VIN = 100mVP-P -16 -18 1 10 100 FREQUENCY (Hz) Maxim Integrated 1k SMALL-SIGNAL RESPONSE 0 1s /div 100 10 FREQUENCY (Hz) 6 0.2µV/div 100 125 150 20 FREQUENCY (Hz) MAX44250 toc16 75 25 10 100 1k 10k 100k 1M 10M 100M TEMPERATURE (°C) INPUT VOLTAGE 0.1Hz TO 10Hz NOISE 50 0 0.1 100 125 150 25 30 -60 0 -25 0 INPUT VOLTAGE NOISE vs. FREQUENCY -20 -40 RL = 10kI to VDD/2 -50 -25 TEMPERATURE (°C) OPEN-LOOP GAIN vs. FREQUENCY OPEN-LOOP GAIN (dB) 14 8 MAX44250 toc14 16 6 180 160 MAX44250 toc13 18 4 OUTPUT SINK CURRENT (mA) MAX44250 toc15 4 RL = 10kI to VDD/2 MAX44250 toc18 2 OUTPUT SOURCE CURRENT (mA) INPUT VOLTAGE NOISE (nV/√Hz) 0 VOL (mV) 30 VOH (mV) OUTPUT VOLTAGE LOW (mV) 500 35 MAX44250 toc11 300 MAX44250 toc10 OUTPUT VOLTAGE HIGH (mV) 600 OUTPUT VOLTAGE SWING HIGH vs. TEMPERATURE OUTPUT VOLTAGE LOW vs. OUTPUT SINK CURRENT MAX44250 toc12 OUTPUT VOLTAGE HIGH vs. OUTPUT SOURCE CURRENT (VDD - VOH) 1k 10k 1 10 100 1k 10k 100k 1M 10M 100M FREQUENCY (Hz) 7 MAX44250/MAX44251/MAX44252 20V, Ultra-Precision, Low-Noise Op Amps Typical Operating Characteristics (continued) (VDD = 10V, VSS = 0V, outputs have RL = 10kI to VDD/2. TA = +25NC, unless otherwise specified.) SMALL-SIGNAL STEP RESPONSE vs. TIME LARGE-SIGNAL RESPONSE MAX44250 toc20 MAX44250 toc19 0 -5 MAX44250 toc21 AV = 1V/V VIN = 100mVP-P VOLTAGE (100mV/div) -10 -15 -20 -25 -30 -35 AV = 1V/V VIN = 2VP-P INPUT INPUT VOLTAGE (1V/div) 5 MAGNITUDE (dB) LARGE-SIGNAL STEP RESPONSE vs. TIME OUTPUT OUTPUT -40 VIN = 2VP-P -45 -50 0.1 1 10 100 1k 10k 100k 1M 10M 100M TIME (2µs/div) TIME (2µs/div) TOTAL HARMONIC DISTORTION vs. FREQUENCY TOTAL HARMONIC DISTORTION vs. INPUT VOLTAGE FREQUENCY (Hz) -105 -110 MAGNITUDE (dB) VOLTAGE (1V/div) VSS = 5V -115 -120 -125 VOFFSET (10mV/div) 100 10k TIME (10µs/div) STABILITY vs. CAPACITIVE AND RESISTIVE LOAD IN PARALLEL WITH CL STABILITY vs. CAPACITIVE AND RISO IN SERIES WITH CLOAD 7 UNSTABLE 40 5 4 UNSTABLE 2 20 100 1k CAPACITIVE LOAD (pF) Maxim Integrated 10k 1.25 1.50 1.75 2.00 80 70 60 50 40 30 10 0 0 0 1.00 20 1 10 0.75 MAX44251 EMIRR 3 30 0.50 INPUT VOLTAGE (V) EMIRR (dB) STABLE 50 RISO (I) 60 STABLE 6 70 0.25 100k MAX44250 toc26 8 MAX44250 toc25 80 RESISTIVE LOAD (kI) 1k FREQUENCY (Hz) 90 -80 -140 -140 100 -60 -120 -135 25µs -40 -100 -130 0V VCC = 3.3V -20 MAGNITUDE (dB) VDD = VSS = 0V 0 MAX44250 toc23 -100 VDD = 5V MAX44250 toc27 MAX44250 toc22 SUPPLY VOLTAGE (5V/div) 0V MAX44250 toc24 POWER-UP TIME 100 1k 10k CAPACITIVE LOAD (pF) 100k 10 100 1000 10,000 FREQUENCY (MHz) 8 MAX44250/MAX44251/MAX44252 20V, Ultra-Precision, Low-Noise Op Amps Pin Configurations TOP VIEW + OUTA 1 5 VDD MAX44250 VSS 2 INA+ 3 4 N.C. 1 INAINA+ 2 3 VSS 4 + 8 MAX44250 N.C. 7 VDD 6 OUTA 5 N.C. INA- 8 µMAX 5 SOT23 OUTA 1 + OUTA 1 8 VDD INA- 2 7 OUTB INA+ 3 6 INB- VSS 4 5 INB+ MAX44251 + INA- 2 OUTA 1 INA- 2 INA+ 3 VSS 4 + 8 MAX44251 VDD 7 OUTB 6 INB- 5 INB+ 8 µMAX 8 SOT23 14 OUTD MAX44252 13 IND- INA+ 3 12 IND+ VDD 4 11 VSS INB+ 5 10 INC+ INB- 6 9 INC- OUTB 7 8 OUTC 14 SO Pin Description PIN MAX44250 MAX44251 MAX44252 NAME FUNCTION 5 SOT23 8 µMAX 8 SOT23 8 µMAX 14 SO 1 6 1 1 1 OUTA 4 2 2 2 2 INA- Channel A Negative Input 3 3 3 3 3 INA+ Channel A Positive Input 2 4 4 4 11 VSS Negative Supply Voltage Channel A Output — — 5 5 5 INB+ Channel B Positive Input — — 6 6 6 INB- Channel B Negative Input — — 7 7 7 OUTB 5 7 8 8 4 VDD Channel B Output Positive Supply Voltage — — — — 8 OUTC — — — — 9 INC- Channel C Negative Input — — — — 10 INC+ Channel C Positive Input Channel D Positive Input — — — — 12 IND+ — — — — 13 IND- — — — — 14 OUTD — 1, 5, 8 — — — N.C. Maxim Integrated Channel C Output Channel D Negative Input Channel D Output No Connection 9 MAX44250/MAX44251/MAX44252 20V, Ultra-Precision, Low-Noise Op Amps Detailed Description The MAX44250/MAX44251/MAX44252 are high-precision amplifiers that have less than 3FV of typical inputreferred offset and low flicker noise. These characteristics are achieved through an autozeroing technique that samples and finds repeating patterns of signal to cancel the input offset voltage and 1/f noise of the amplifier. Autozero The ICs feature an autozero circuit that allows the devices to achieve less than 6FV (max) of input offset voltage at room temperature and eliminate the 1/f noise. Electromagnetic interference (EMI) noise occurs at higher frequency that results in malfunction or degradation of electrical equipment. The ICs have an input EMI filter to avoid the output getting affected by radio frequency interference. The EMI filter composed of passive devices presents significant higher impedance to higher frequency. High Supply Voltage Range The ICs feature 1.15mA current consumption per channel and a voltage supply range from either 2.7V to 20V single supply or ±1.35V to ±10V split supply. Applications Information Noise Suppression Flicker noise, inherent in all active devices, is inversely proportional to frequency presented. Charges at the oxide-silicon interface that are trapped-and-released by MOSFET oxide occurs at low frequency more often. For this reason, flicker noise is also called 1/f noise. The ICs are ultra-high-precision operational amplifiers with a high supply voltage range designed for load cell, medical instrumentation and precision instrument applications. These devices are also designed to interface with pressure transducers and are ideal for precision weight scale application as shown in Figure 1. 3.3V +10V MAX44251 3V BUFFER R R1 10V -10V RG 50RG MAX44251 BUFFER VDD BUFFER VDD VREF VIN+ R +10V MAX6126 +10V R 50RG VOUT MICROPROCESSOR MAX11211OUTPUT R 1.5V -10V VIN- VSS C1 MAX44251 -10V Figure 1. Weight Scale Application Circuit Maxim Integrated 10 MAX44250/MAX44251/MAX44252 20V, Ultra-Precision, Low-Noise Op Amps ADC Buffer Amplifier The MAX44250/MAX44251/MAX44252's low input offset voltage, low noise, and fast settling time make these amplifiers ideal for ADC buffers. Weigh scales are one application that often require a low-noise, high-voltage amplifier in front of an ADC. Figure 1 details an example of a load cell and amplifier driven from the same Q10V supplies, along with the MAX11211 18-bit delta sigma ADC. Load cells produce a very small voltage change at their outputs, therefore driving the excitation source with a higher voltage produces a wider dynamic range that can be measured at the ADC inputs. The MAX11211 ADC operates from a single 2.7V to 3.6V analog supply, offers 18-bit noise-free resolution and 0.86mW power dissipation. The MAX11211 also offers > 100dB rejection at 50Hz and 60Hz. This ADC is part of a family of 16-, 18-, 20-, and 24-bit delta sigma ADCs with high precision and < 1mW power dissipation. The MAX44250/MAX44251/MAX44252's low input offset voltage and low noise allow a gain circuit prior to the MAX11211 without losing any dynamic range at the ADC. The ICs, with a typical offset drift of 5nV/°C, guarantee that the drift over a 10°C range is only 50nV. Setting this equal to 0.5 LSB in a 18-bit system yields a full-scale range of 13mV. With a single 10V supply, an acceptable closed-loop gain of 770V/V provides sufficient gain while maintaining headroom. Precision Low-Side Current Sensing The ICs’ autozero feature produces ultra-low offset voltage and drift, making them ideal for precision current-sensing applications. Figure 2 shows the ICs in a low-side current-sense configuration. This circuit produces an accurate output voltage, VOUT equal to ILOAD x RSENSE x (1 + R2/R1). R2 VSUPPLY R1 ILOAD Error Budget Example When using the ICs as an ADC buffer in strain gauge application, the temperature drift should be taken into consideration to determine maximum input signal. A typical strain gauge has sensitivity specification of just 2mV/V at rated out load. This means that when the strain gauge load cell is powered with 10V, the full-scale output voltage is 20mV. In this application, both offset voltage and drift are critical parameters that directly affect the accuracy of measurement. Even though offset voltage could be calibrated out, its drift over temperature is still a problem. Maxim Integrated OUT MAX44251 MAX44252 RSENSE Figure 2. Low-Side Current Sensing 11 MAX44250/MAX44251/MAX44252 20V, Ultra-Precision, Low-Noise Op Amps Functional Diagrams TOP VIEW + + OUT 1 5 OUTA 1 VDD VSS 2 IN+ 3 4 IN- 8 VDD INA- 2 7 OUTB INA+ 3 6 INB- VSS 4 5 INB+ MAX44251 MAX44250 + OUTA + 1 14 OUTD 8 N.C. INA- 2 13 IND- IN- 2 7 VDD INA+ 3 12 IND+ IN+ 3 6 OUT VDD 4 VSS 4 5 N.C. INB+ 5 10 INC+ INB- 6 9 INC- OUTB 7 8 OUTC N.C. 1 MAX44250 Chip Information MAX44252 11 VSS Ordering Information PROCESS: BiCMOS TEMP RANGE PINPACKAGE TOP MARK MAX44250AUK+ -40NC to +125NC 5 SOT23 AFMA MAX44250AUA+ -40NC to +125NC 8 FMAX — MAX44251AKA+ -40NC to +125NC 8 SOT23 AERC MAX44251AUA+ -40NC to +125NC 8 FMAX — MAX44252ASD+ -40NC to +125NC 14 SO — PART +Denotes a lead(Pb)-free/RoHS-compliant package. Maxim Integrated 12 MAX44250/MAX44251/MAX44252 20V, Ultra-Precision, Low-Noise Op Amps Package Information For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN 5 SOT23 U5+1 21-0057 90-0174 8 SOT23 K8+5 21-0078 90-0176 8 FMAX U8+1 21-0036 90-0092 14 SO S14M+5 21-0041 90-0096 Maxim Integrated 13 MAX44250/MAX44251/MAX44252 20V, Ultra-Precision, Low-Noise Op Amps Revision History REVISION NUMBER REVISION DATE 0 10/11 Initial release 1 12/11 Released the MAX44252 and updated the Typical Operating Characteristics. 2 8/12 Added the MAX44250 to the data sheet, added MAX44251 EMIRR graph to Typical Operating Characteristics, and revised Figure 2. 1–16 3 4/13 Updated General Description, Typical Operating Circuit, and Figure 1. 1, 10 DESCRIPTION PAGES CHANGED — 5, 6, 11 Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000 © 2013 Maxim Integrated 14 The Maxim logo and Maxim Integrated are trademarks of Maxim Integrated Products, Inc.