INA INA 337 INA337 INA338 338 SBOS248 – JUNE 2002 Wide-Temperature, Precision INSTRUMENTATION AMPLIFIER FEATURES DESCRIPTION ● PRECISION LOW OFFSET: 100µV (max) LOW OFFSET DRIFT: 0.4µV/°C (max) EXCELLENT LONG-TERM STABILITY VERY-LOW 1/f NOISE The INA337 and INA338 (with shutdown) are high temperature, high-performance, low-cost, precision instrumentation amplifiers. They are true single-supply instrumentation amplifiers with very-low DC errors and input common-mode ranges that extends beyond the positive and approaches the negative rail. These features make them suitable for applications ranging from general-purpose to high-accuracy. ● SMALL SIZE microPACKAGE: MSOP-8, MSOP-10 ● LOW COST APPLICATIONS ● LOW-LEVEL TRANSDUCER AMPLIFIER FOR BRIDGES, LOAD CELLS, THERMOCOUPLES ● WIDE DYNAMIC RANGE SENSOR MEASUREMENTS ● HIGH-RESOLUTION TEST SYSTEMS ● WEIGH SCALES ● MULTI-CHANNEL DATA ACQUISITION SYSTEMS ● MEDICAL INSTRUMENTATION ● AUTOMOTIVE APPLICATIONS ● GENERAL-PURPOSE Excellent long-term stability and very low 1/f noise assure low offset voltage and drift throughout the life of the product. The INA337 (without shutdown) comes in the MSOP-8 package. The INA338 (with shutdown) is offered in MSOP-10. Both are specified over the temperature range, –40°C to +125°C. INA337 AND INA338 RELATED PRODUCTS PRODUCT FEATURES INA326 INA114 INA118 INA122 INA128 INA321 Precision, Rail-to-Rail I/O, 2.4mA IQ 50µV VOS, 0.5nA IB, 115dB CMR, 3mA IQ, 0.25µV/°C drift 50µV VOS, 1nA IB, 120dB CMR, 385µA IQ, 0.5µV/°C drift 250µV VOS, –10nA IB, 85µA IQ, Rail-to-Rail Output, 3µV/°C drift 50µV VOS, 2nA IB, 125dB CMR, 750µA IQ, 0.5µV/°C drift 500µV VOS, 0.5pA IB, 94dB CMRR, 60µA IQ, Rail-to-Rail Output V+ VIN– 2 1 R1 VIN+ V– 7 4 6 INA337 8 3 5 R2 VO G = 2(R2/R1) C2 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. Copyright © 2002, Texas Instruments Incorporated PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. www.ti.com PACKAGE/ORDERING INFORMATION PRODUCT PACKAGE-LEAD PACKAGE DESIGNATOR(1) SPECIFIED TEMPERATURE RANGE PACKAGE MARKING ORDERING NUMBER TRANSPORT MEDIA, QUANTITY MSOP-8 DGK –40°C to +125°C BIM " " " " INA337AIDGKT INA337AIDGKR Tape and Reel, 250 Tape and Reel, 2500 MSOP-10 DGS –40°C to +125°C BIL " " " " INA338AIDGST INA338AIDGSR Tape and Reel, 250 Tape and Reel, 2500 INA337 " INA338 " NOTE: (1) For the most current specifications and package information, refer to our web site at www.ti.com. ABSOLUTE MAXIMUM RATINGS(1) Supply Voltage .................................................................................. +5.5V Signal Input Terminals: Voltage(2) ......................................... –0.5V to (V+) + 0.5V Current(2) ........................................................................ ±10mA Output Short-Circuit ................................................................. Continuous Operating Temperature Range ....................................... –40°C to +150°C Storage Temperature Range .......................................... –65°C to +150°C Junction Temperature .................................................................... +150°C Lead Temperature (soldering, 10s) ............................................... +300°C NOTES: (1) Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may degrade device reliability. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those specified is not implied. (2) Input terminals are diode clamped to the power-supply rails. Input signals that can swing more than 0.5V beyond the supply rails should be current limited to 10mA or less. ELECTROSTATIC DISCHARGE SENSITIVITY This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. PIN CONFIGURATION Top View 8 R1 R1 1 10 R1 7 V+ VIN– 2 9 V+ 3 6 VO VIN+ 3 8 VO 4 5 R2 V– 4 7 R2 (Connect to V+) 5 6 Enable R1 1 VIN– 2 VIN+ V– INA337 MSOP-8 INA338 MSOP-10 2 INA337, INA338 www.ti.com SBOS222A ELECTRICAL CHARACTERISTICS: VS = +2.7V to +5.5V BOLDFACE limits apply over the specified temperature range, TA = –40°C to +125°C At TA = +25°C, RL = 10kΩ, G = 100 (R1 = 2kΩ, R2 = 100kΩ), external gain set resistors, and IACOMMON = VS /2, with external equivalent filter corner of 1kHz filters, unless otherwise noted. INA337AIDGK, INA338AIDGS PARAMETER CONDITION INPUT VS = +5V, VCM = VS /2 Offset Voltage, RTI VOS Over Temperature vs Temperature dVOS/dT vs Power Supply PSR VS = +2.7V to +5.5V, VCM = VS /2 Long-Term Stability Input Impedance, Differential Common-Mode Input Voltage Range Safe Input Voltage Common-Mode Rejection CMR VS = +5V, VCM = (V–) + 0.25V to (V+) + 0.1V Over Temperature INPUT BIAS CURRENT Bias Current vs Temperature Offset Current IB VCM = VS /2 VS = +5V IOS VS = +5V NOISE Voltage Noise, RTI f = 10Hz f = 100Hz f = 1kHz f = 0.01Hz to 10Hz Voltage Noise, RTI f = 10Hz f = 100Hz f = 1kHz f = 0.01Hz to 10Hz Current Noise, RTI f = 1kHz f = 0.01Hz to 10Hz Output Ripple, VO Filtered(2) MAX UNITS ±140 ±0.4 ±100 µV µV µV/°C µV/V (V+) + 0.1 (V+) + 0.5 Ω || pF Ω || pF V V dB dB ±20 ±0.1 ±20 ±3 See Note (1) 1010 || 2 1010 || 14 (V–) + 0.25 (V–) –0.5 106 100 120 ±0.2 See Typical Characteristics ±0.2 ±2 nA ±2 nA 33 33 33 0.8 nV/ √Hz nV/ √Hz nV/ √Hz µVp-p 120 97 97 4 nV/ √Hz nV/ √Hz nV/ √Hz µVp-p 0.15 4.2 See Applications Information pA/ √Hz pAp-p RS = 0Ω, G = 10, R1 = 20kΩ, R2 = 100kΩ G = 2(R2/R1) < 0.1 G = 10, 100, VS = +5V, VO = 0.25V to 4.925V G = 10, 100, VS = +5V, VO = 0.25V to 4.925V G = 10, 100, VS = +5V, VO = 0.25V to 4.925V OUTPUT Voltage Output Swing from Positive Rail Over Temperature Voltage Output Swing from Negative Rail Over Temperature Capacitive Load Drive Short-Circuit Current ISC RL = 10kΩ, VS = 5V RL = 10kΩ, VS = 5V INTERNAL OSCILLATOR Frequency of Auto-Correction Accuracy BW G = 1 to 1k SR VS = 5V, All Gains, CL = 100pF tS 1kHz Filter, G = 1 to 1k, VO = 2V step, CL = 100pF 10kHz Filter, G = 1 to 1k, VO = 2V step, CL = 100pF 1kHz Filter, 50% Output Overload, G = 1 to 1k 10kHz Filter, 50% Output Overload, G = 1 to 1k INA337, INA338 SBOS222A TYP RS = 0Ω, G = 100, R1 = 2kΩ, R2 = 100kΩ GAIN Gain Equation Range of Gain Gain Error(3) vs Temperature Nonlinearity FREQUENCY RESPONSE Bandwidth(4), –3dB Slew Rate(4) Settling Time(4), 0.1% 0.01% 0.1% 0.01% Overload Recovery(4) MIN www.ti.com 0.08 ±6 ±0.003 (V+) – 0.075 (V+) – 0.075 (V–) + 0.25 (V–) + 0.25 (V+) – 0.01 > 10000 ±0.2 ±25 ±0.01 V/V % ppm/°C % of FS 500 ±25 V V V V pF mA 90 ±20 kHz % 1 Filter Limited 0.95 1.3 130 160 30 5 kHz (V+) + 0.01 ms ms µs µs µs µs 3 ELECTRICAL CHARACTERISTICS: VS = +2.7V to +5.5V (Cont.) BOLDFACE limits apply over the specified temperature range, TA = –40°C to +125°C At TA = +25°C, RL = 10kΩ, G = 100 (R1 = 2kΩ, R2 = 100kΩ), external gain set resistors, and IACOMMON = VS /2, with external equivalent filter corner of 1kHz filters, unless otherwise noted. INA337AIDGK, INA338AIDGS PARAMETER POWER SUPPLY Specified Voltage Range Quiescent Current Over Temperature CONDITION TYP MAX UNITS 2.4 +5.5 3.4 3.7 V mA mA 0.25 V V µs µs µA +2.7 IQ SHUTDOWN Disable (Logic-Low Threshold) Enable (Logic-High Threshold) Enable Time(5) Disable Time Shutdown Current and Enable Pin Current TEMPERATURE RANGE Specified Range Operating Range Storage Range Thermal Resistance MIN IO = 0, Diff VIN = 0V, VS = +5V 1.6 75 100 2 VS = +5V, Disabled –40 –40 –65 θJA MSOP-8 Surface-Mount 5 +125 +150 +150 150 °C °C °C °C/W NOTES: (1) 1000-hour life test at 150°C demonstrated randomly distributed variation in the range of measurement limits—approximately 10µV. (2) See Applications Information section, Figures 1 and 2. (3) Does not include error and TCR of external gain-setting resistors. (4) Dynamic response is limited by filtering. Higher bandwidths can be achieved by adjusting the filter. (5) See Typical Characteristics, “Input Offset Voltage vs Warm-Up Time”. 4 INA337, INA338 www.ti.com SBOS222A TYPICAL CHARACTERISTICS At TA = 25°C, VS = +5V, Gain = 100, RL = 10kΩ with external equivalent filter corner of 1kHz filters, unless otherwise noted. GAIN vs FREQUENCY 1kHz FILTER GAIN vs FREQUENCY 10kHz FILTER 80 80 60 60 G = 1k G = 1k 40 Gain (dB) Gain (dB) 40 G = 100 20 G = 10 0 G = 100 20 G = 10 0 G=1 G=1 –20 –20 –40 –40 10 100 1k 10k Frequency (Hz) 100k 1M 10 100 1k 10k Frequency (Hz) CMR vs FREQUENCY 1kHz FILTER 100k 1M 100k 1M CMR vs FREQUENCY 10kHz FILTER 160 160 G = 1k 140 140 G = 100 120 CMR (dB) 100 G = 10 80 G=1 G = 1k 100 80 G = 100 60 60 40 40 G=1 20 20 10 100 1k 10k Frequency (Hz) 100k 1M 10 Input-Referred Voltage Noise (nV/√Hz) G = 100, 1k 100 PSR (dB) 80 G = 10 G=1 60 40 Filter Frequency 10kHz 1kHz 20 100 1k 10k Frequency (Hz) INPUT-REFERRED VOLTAGE NOISE AND INPUT BIAS CURRENT NOISE vs FREQUENCY 10kHz Filter POWER-SUPPLY REJECTION vs FREQUENCY 120 G = 10 0 10k 1 Current Noise (all gains) 1k 0.1 G=1 G = 10 100 0.01 G = 100 G = 1000 10 10 100 1k Frequency (Hz) 10k 100k INA337, INA338 SBOS222A www.ti.com Input Bias Current Noise (pA/√Hz) CMR (dB) 120 0.001 1 10 100 Frequency (Hz) 1k 10k 5 TYPICAL CHARACTERISTICS (Cont.) At TA = 25°C, VS = +5V, Gain = 100, RL = 10kΩ with external equivalent filter corner of 1kHz filters, unless otherwise noted. INPUT OFFSET VOLTAGE vs WARM-UP TIME 10kHz FILTER, G = 100 INPUT OFFSET VOLTAGE vs TURN-ON TIME 1kHz FILTER, G = 100 Input Offset Voltage (20µV/div) Input Offset Voltage (20µV/div) Filter Settling Time Device Turn-On Time (75µs) 0 1 Turn-On Time (ms) Device Turn-On Time Filter Settling Time 0 2 SMALL-SIGNAL RESPONSE G = 1, 10, AND 100 0.1 0.2 0.3 Warm-Up Time (ms) 0.4 SMALL-SIGNAL STEP RESPONSE G = 1000 50mV/div 1kHz Filter 50mV/div 1kHz Filter 10kHz Filter 500µs/div 500µs/div LARGE-SIGNAL RESPONSE G = 1 TO 1000 0.01Hz TO 10Hz VOLTAGE NOISE 2V/div 200nV/div 1kHz Filter 10kHz Filter 10s/div 500µs/div 6 INA337, INA338 www.ti.com SBOS222A TYPICAL CHARACTERISTICS (Cont.) At TA = 25°C, VS = +5V, Gain = 100, RL = 10kΩ with external equivalent filter corner of 1kHz filters, unless otherwise noted. OFFSET VOLTAGE PRODUCTION DISTRIBUTION G=1 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 –10,000 –9000 –8000 –7000 –6000 –5000 –4000 –3000 –2000 –1000 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10,000 Population Population OFFSET VOLTAGE DRIFT PRODUCTION DISTRIBUTION G=1 Offset Voltage Drift (µV/°C) Offset Voltage (µV) OFFSET VOLTAGE PRODUCTION DISTRIBUTION G = 10 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 –1000 –900 –800 –700 –600 –500 –400 –300 –200 –100 0 100 200 300 400 500 600 700 800 900 1000 Population Population OFFSET VOLTAGE DRIFT PRODUCTION DISTRIBUTION G = 10 Offset Voltage Drift (µV/°C) Offset Voltage (µV) OFFSET VOLTAGE PRODUCTION DISTRIBUTION G = 100 and 1000 0.0 0.2 0.4 0.6 0.8 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.26 0.28 0.3 0.32 0.34 0.36 0.38 0.4 100 90 80 70 60 50 40 30 20 10 0 10 20 30 40 50 60 70 80 90 100 Population Population OFFSET VOLTAGE DRIFT PRODUCTION DISTRIBUTION G = 100 and 1000 Offset Voltage (µV) Offset Voltage Drift (µV/°C) INA337, INA338 SBOS222A www.ti.com 7 TYPICAL CHARACTERISTICS (Cont.) At TA = 25°C, VS = +5V, Gain = 100, RL = 10kΩ with external equivalent filter corner of 1kHz filters, unless otherwise noted. VOUT (dBV) Population 100 100 110 31.6 120 1 130 0.316 140 0.10 150 0.03 160 0.01 170 0.003 –200 –180 –160 –140 –120 –100 –80 –60 –40 –20 0 20 40 60 80 100 120 140 160 180 200 180 0 200k 400k 600k Frequency (Hz) Gain Error (m%) QUIESCENT CURRENT vs TEMPERATURE INPUT BIAS CURRENT vs TEMPERATURE 3.0 2.0 VS = +5V 1.5 2.5 1.0 IB+ 0.5 VS = +2.7V IB (nA) IQ (mA) 2.0 1.5 0 –0.5 1.0 IB– –1.0 0.5 0 –50 0.001 1M 800k –1.5 –2.0 –25 0 25 50 Temperature (°C) 75 100 –40 125 –20 0 20 40 60 80 100 120 Temperature (°C) OUTPUT SWING TO THE NEGATIVE RAIL vs TEMPERATURE Output Swing to Negative Rail (mV) 16 14 12 10 8 6 4 2 0 –40 –20 0 20 40 60 80 100 120 Temperature (°C) 8 INA337, INA338 www.ti.com SBOS222A VOUT (µVrms) INPUT-REFERRED RIPPLE SPECTRUM G = 100 GAIN ERROR PRODUCTION DISTRIBUTION APPLICATIONS INFORMATION SETTING THE GAIN The INA337 is a 2-stage amplifier with each stage gain set by R1 and R2, respectively (see Figure 4, “Inside the INA337", for details.) Overall gain is described by the equation: Figure 1 shows the basic connections required for operation of the INA337. A 0.1µF capacitor, placed close to and across the power-supply pins is strongly recommended for highest accuracy. RoCo is an output filter that minimizes auto-correction circuitry noise. This output filter may also serve as an antialiasing filter ahead of an Analog-to-Digital (A/D) converter. It is also optional based on desired precision. G= 2R2 R1 (1) The stability and temperature drift of the external gain-setting resistors will affect gain by an amount that can be directly inferred from the gain equation (1). The output reference terminal is taken at the low side of R2 (IACOMMON). Resistor values for commonly used gains are shown in Figure 1. Gain-set resistor values for best performance are different for +5V single-supply and for ±2.5V dual-supply operation. Optimum value for R1 can be calculated by: The INA337 uses a unique internal topology to achieve excellent common-mode rejection (CMR). Unlike conventional instrumentation amplifiers, CMR is not affected by resistance in the reference connections. See “Inside the INA337” for further detail. To achieve best high-frequency CMR, minimize capacitance on pins 1 and 8. R1 = VIN, MAX/12.5µA (2) where R1 must be no less than 2kΩ. Dual-Supply Operation DESIRED GAIN R1 (Ω) 0.1 0.2 0.5 1 2 5 10 20 50 100 200 500 1000 2000 5000 10000 400k 400k 400k 200k 100k 40k 20k 10k 4k 2k 2k 2k 2k 2k 2k 2k R2 || C2 (Ω || nF) 20k || 40k || 100k || 100k || 100k || 100k || 100k || 100k || 100k || 100k || 200k || 500k || 1M || 2M || 5M || 10M || 5 2.5 1 1 1 1 1 1 1 1 0.5 0.2 0.1 0.05 0.02 0.01 –2.5V +2.5V 0.1µF VIN– R1 VIN+ 2 7 1 4 6 INA337 RO VO 100Ω VO Filtered CO(1) 1µF 8 5 3 G = 2(R2/R1) fO = 1kHz C2(1) R2 IACOMMON(2) NOTES: (1) C2 and CO combine to form a 2-pole response that is –3dB at 1kHz. Each individual pole is at 1.5kHz. (2) Output voltage is referenced to IACOMMON (see text). Single-Supply Operation DESIRED GAIN R1 (Ω) 0.1 0.2 0.5 1 2 5 10 20 50 100 200 500 1000 2000 5000 10000 400k 400k 400k 400k 200k 80k 40k 20k 8k 4k 2k 2k 2k 2k 2k 2k V+ R2 || C2 (Ω || nF) 20k || 40k || 100k || 200k || 200k || 200k || 200k || 200k || 200k || 200k || 200k || 500k || 1M || 2M || 5M || 10M || 5 2.5 1 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.2 0.1 0.05 0.02 0.01 V– 0.1µF VIN– 2 7 1 R1 4 6 INA337 RO VO 100Ω VIN+ VO Filtered CO(1) 8 5 3 G = 2(R2/R1) 1µF (3) R2 fO = 1kHz C2(1) IACOMMON(2) NOTES: (1) C2 and CO combine to form a 2-pole response that is –3dB at 1kHz. Each individual pole is at 1.5kHz. (2) Output voltage is referenced to IACOMMON (see text). (3) Output pedestal required for measurement near zero (see Figure 6). FIGURE 1. Basic Connections. NOTE: Connections for INA338 differ—see Pin Configuration for detail. INA337, INA338 SBOS222A www.ti.com 9 Following this design procedure for R1 produces the maximum possible input stage gain for best accuracy and lowest noise. Circuit layout and supply bypassing can affect performance. Minimize the stray capacitance on pins 1 and 8. Use recommended supply bypassing, including a capacitor directly from pin 7 to pin 4 (V+ to V–), even with dual (split) power supplies (see Figure 1). DYNAMIC PERFORMANCE The typical characteristic “Gain vs Frequency” shows that the INA337 has nearly constant bandwidth regardless of gain. This results from the bandwidth limiting from the recommended filters. NOISE PERFORMANCE Internal auto-correction circuitry eliminates virtually all 1/f noise (noise that increases at low frequency) in gains of 100 or greater. Noise performance is affected by gain-setting resistor values. Follow recommendations in the “Setting Gain” section for best performance. Total noise is a combination of input stage noise and output stage noise. When referred to the input, the total mid-band noise is: VN = 33nV / Hz + 800nV / Hz G (3) The output noise has some 1/f components that affect performance in gains less than 10. See typical characteristic “Input-Referred Voltage Noise vs Frequency.” High-frequency noise is created by internal auto-correction circuitry and is highly dependent on the filter characteristics chosen. This may be the dominant source of noise visible when viewing the output on an oscilloscope. Low cutoff frequency filters will provide lowest noise. Figure 2 shows the typical noise performance as a function of cutoff frequency. Applications sensitive to the spectral characteristics of highfrequency noise may require consideration of the spurious frequencies generated by internal clocking circuitry. “Spurs” occur at approximately 90kHz and its harmonics (see typical characteristic “Input Referred Ripple”) which may be reduced by additional filtering below 1kHz. Insufficient filtering at pin 5 can cause nonlinearity with large output voltage swings (very near the supply rails). Noise must be sufficiently filtered at pin 5 so that noise peaks do not “hit the rail” and change the average value of the signal. Figure 2 shows guidelines for filter cutoff frequency. HIGH-FREQUENCY NOISE C2 and CO form filters to reduce internally generated autocorrection circuitry noise. Filter frequencies can be chosen to optimize the tradeoff between noise and frequency response of the application, as shown in Figure 2. The cutoff frequencies of the filters are generally set to the same frequency. Figure 2 shows the typical output noise for four gains as a function of the –3dB cutoff frequency of each filter response. Small signals may exhibit the addition of internally generated auto-correction circuitry noise at the output. This noise, combined with broadband noise, becomes most evident in higher gains with filters of wider bandwidth. INPUT BIAS CURRENT RETURN PATH The input impedance of the INA337 is extremely high— approximately 1010Ω. However, a path must be provided for the input bias current of both inputs. This input bias current is approximately ±0.2nA. High input impedance means that this input bias current changes very little with varying input voltage. Input circuitry must provide a path for this input bias current for proper operation. Figure 3 shows provisions for an input bias current path in a thermocouple application. Without a bias current path, the inputs will float to an undefined potential and the output voltage may not be valid. Total Output Noise (µVRMS) 1k G = 1000 100 Thermocouple 10 5 G = 100 G = 10 G=1 1 1 10 100 1k Required Filter Cutoff Frequency (Hz) 10k FIGURE 2. Total Output Noise vs Filter Cutoff Frequency. 10 INA337 FIGURE 3. Providing Input Bias Current Return Path. INA337, INA338 www.ti.com SBOS222A INPUT AND OUTPUT VOLTAGE INPUT PROTECTION The INA337 and INA338 feature nearly rail-to-rail input behavior, with the linear input voltage range extending from 0.25V above the negative rail to 0.1V above the positive rail. The output is able to swing to within 0.25V of the negative rail and 0.075V of the positive rail. See Typical Characteristics Curve “Output Swing to the Negative Rail” for additional detail. The inputs of the INA337 are protected with internal diodes connected to the power-supply rails. These diodes will clamp the applied signal to prevent it from damaging the input circuitry. If the input signal voltage can exceed the power supplies by more than 0.5V, the input signal current should be limited to less than 10mA to protect the internal clamp diodes. This can generally be done with a series input resistor. Some signal sources are inherently current-limited and do not require limiting resistors. INSIDE THE INA337 A simplified diagram shows the basic circuit function. The differential input voltage, (VIN+) – (VIN–) is applied across R1. The signal-generated current through R1 comes from A1 and A2’s output stages. A2 combines the current in R1 with a mirrored replica of the current from A1. The resulting current in A2’s output and associated current mirror is two times the current in R1. This current flows in (or out) of pin 5 into R2. The resulting gain equation is: The INA337 uses a new, unique internal circuit topology that provides near rail-to-rail input. Unlike other instrumentation amplifiers, it can linearly process inputs from 0.25V above the negative rail to 0.1V beyond the positive rail. Conventional instrumentation amplifier circuits cannot deliver such performance, even if rail-to-rail op amps are used. The ability to reject common-mode signals is derived in most instrumentation amplifiers through a combination of amplifier CMR and accurately matched resistor ratios. The INA337 converts the input voltage to a current. Currentmode signal processing provides rejection of commonmode input voltage and power-supply variation without accurately matched resistors. G= 2R2 R1 Amplifiers A1, A2 and their associated mirrors are powered from internal charge-pumps that provide voltage supplies that are beyond the positive negative supply. As a result, the voltage developed on R2 can actually swing 100mV above the positive power-supply rail. A3 provides a buffered output of the voltage on R2. A3’s input stage is also operated from the charge-pumped power supplies for true rail-to-rail operation. The topology of the INA337 avoids aliasing issues that appear in instrumentation amplifiers that use sampled data techniques. V+ V– 0.1µF Current Mirror IR1 VIN– IR1 A1 Current Mirror IR1 R1 Current Mirror IR1 2IR1 2IR1 VIN+ A2 2IR1 A3 2IR1 Current Mirror VO 2IR1 R2 C2 IACOMMON FIGURE 4. Simplified Circuit Diagram. INA337, INA338 SBOS222A www.ti.com 11 FILTERING Filtering can be adjusted through selection of R2C2 and ROCO for the desired tradeoff of noise and bandwidth. Adjustment of these components will result in more or less ripple due to auto-correction circuitry noise and will also affect broadband noise. Filtering limits slew rate, settling time, and output overload recovery time. R0 R1 5 VREF = 10V to 5V C0 R´2 It is generally desirable to keep the resistance of RO relatively low to avoid DC gain error created by the subsequent stage loading. This may result in relatively high values for CO to produce the desired filter response. The impedance of ROCO can be scaled higher to produce smaller capacitor values if the load impedance is very high. Certain capacitor types greater than 0.1µF may have dielectric absorption effects that can significantly increase settling time in high-accuracy applications (settling to 0.01%). Polypropylene, polystyrene, and polycarbonate types are generally good. Certain “high-K” ceramic types may produce slow settling “tails.” Settling time to 0.1% is not generally affected by high-K ceramic capacitors. Electrolytic types are not recommended for C2 and CO. INA337 R2 and R´2 are chosen to create a small pedestal voltage (e.g., 250mV). Gain is determined by the parallel combination of R2 and R´2. R2 C2 G = 2 (R2 || R´2)/R1 FIGURE 6. Output Range Pedestal. +5V RS must be chosen so that the input voltage does not exceed 100mV above the rail. RS INA338 ENABLE FUNCTION IL RO The INA338 can be enabled by applying a logic “High” voltage level to the Enable pin. Conversely, a logic “Low” voltage level will disable the amplifier, reducing its supply current from 2.4mA to typically 2µA. For battery-operated applications, this feature may be used to greatly reduce the average current and extend battery life. This pin should be connected to a valid high or low voltage or driven, not left open circuit. The Enable pin can be modeled as a CMOS input gate as in Figure 5. R1 INA337 5 NOTE: Connection point of V+ will include ( ) or exclude ( ) quiescent current in the measurement as desired. Output pedestal required for measurements near zero (see Figure 6). CO R2 C2 FIGURE 7. High-Side Shunt Measurement of Current Load. V+ 2µA Enable VREF VREF 6 V– RO FIGURE 5. Enable Pin Model. 2kΩ 5 The enable time following shutdown is 75µs plus the settling time due to filters (see Typical Characteristics, “Input Offset Voltage vs Warm-up Time”). Disable time is 100µs. This allows the INA338 to be operated as a “gated” amplifier, or to have its output multiplexed onto a common output bus. When disabled, the output assumes a high-impedance state. A/D Converter INA337 CO 200kΩ G = 2(200kΩ || 200kΩ)/2kΩ = 100 200kΩ C2 INA338 PIN 5 Pin 5 of the INA338 should be connected to V+ to ensure proper operation. 12 FIGURE 8. Output Referenced to VREF/2. INA337, INA338 www.ti.com SBOS222A PACKAGE DRAWINGS MPDS028B – JUNE 1997 – REVISED SEPTEMBER 2001 DGK (R-PDSO-G8) PLASTIC SMALL-OUTLINE PACKAGE 0,38 0,25 0,65 8 0,08 M 5 0,15 NOM 3,05 2,95 4,98 4,78 Gage Plane 0,25 1 0°– 6° 4 3,05 2,95 0,69 0,41 Seating Plane 1,07 MAX 0,15 0,05 0,10 4073329/C 08/01 NOTES: A. B. C. D. All linear dimensions are in millimeters. This drawing is subject to change without notice. Body dimensions do not include mold flash or protrusion. Falls within JEDEC MO-187 INA337, INA338 SBOS222A www.ti.com 13 PACKAGE DRAWINGS (Cont.) MPDS035A – JANUARY 1998 – REVISED SEPTEMBER 2001 DGS (S-PDSO-G10) PLASTIC SMALL-OUTLINE PACKAGE 0,27 0,17 0,50 10 0,08 M 6 0,15 NOM 3,05 2,95 4,98 4,78 Gage Plane 0,25 1 0°– 6° 5 3,05 2,95 0,69 0,41 Seating Plane 1,07 MAX 0,15 0,05 0,10 4073272/B 08/01 NOTES: A. B. C. A. 14 All linear dimensions are in millimeters. This drawing is subject to change without notice. Body dimensions do not include mold flash or protrusion. Falls within JEDEC MO-187 INA337, INA338 www.ti.com SBOS222A PACKAGE OPTION ADDENDUM www.ti.com 3-Oct-2003 PACKAGING INFORMATION ORDERABLE DEVICE STATUS(1) PACKAGE TYPE PACKAGE DRAWING PINS PACKAGE QTY INA337AIDGKR ACTIVE VSSOP DGK 8 2500 INA337AIDGKT ACTIVE VSSOP DGK 8 250 INA338AIDGSR ACTIVE VSSOP DGS 10 2500 INA338AIDGST ACTIVE VSSOP DGS 10 250 (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All products are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment. TI warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with TI’s standard warranty. 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