INA 322 INA322 INA2322 ® www.ti.com microPower, Single-Supply, CMOS INSTRUMENTATION AMPLIFIER FEATURES APPLICATIONS ● LOW COST ● LOW QUIESCENT CURRENT: 40µA/channel Shut Down: < 1µA ● HIGH GAIN ACCURACY: G = 5, 0.07%, 2ppm/°C ● GAIN SET WITH EXTERNAL RESISTORS ● LOW BIAS CURRENT: 10pA ● BANDWIDTH: 500kHz, G = 5V/V ● RAIL-TO-RAIL OUTPUT SWING: (V+) – 0.02V ● WIDE TEMPERATURE RANGE: –55°C to +125°C ● SINGLE VERSION IN MSOP-8 PACKAGE AND DUAL VERSION IN TSSOP-14 PACKAGE ● INDUSTRIAL SENSOR AMPLIFIERS: Bridge, RTD, Thermistor, Position ● PHYSIOLOGICAL AMPLIFIERS: ECG, EEG, EMG ● A/D CONVERTER SIGNAL CONDITIONING ● DIFFERENTIAL LINE RECEIVERS WITH GAIN ● FIELD UTILITY METERS ● PCMCIA CARDS ● COMMUNICATION SYSTEMS ● TEST EQUIPMENT ● AUTOMOTIVE INSTRUMENTATION DESCRIPTION Configured internally for 5V/V gain, the INA322 offers exceptional flexibility with user-programmable external gain resistors. The INA322 reduces common-mode error over frequency and with CMRR remaining high up to 3kHz, line noise and line harmonics are rejected. The INA322 family is a series of low cost, rail-to-rail output, micropower CMOS instrumentation amplifiers that offer wide-range, single-supply, as well as bipolarsupply operation. The INA322 family provides lowcost, low-noise amplification of differential signals with micropower current consumption of 40µA. When shutdown the INA322 has a quiescent current of less than 1µA. Returning to normal operations within nanoseconds, the shutdown feature makes the INA322 optimal for low-power battery or multiplexing applications. The low-power design does not compromise on bandwidth or slew rate, making the INA322 ideal for driving sampling Analog-to-Digital (A/D) converters as well as general-purpose applications. With high precision, low cost, and small packaging, the INA322 outperforms discrete designs, while offering reliability and performance. R1 160kΩ 40kΩ RG 40kΩ R2 160kΩ REF A1 A3 VIN– VOUT A2 VIN+ Gain = 5 + 5(R2/R1) VOUT = (VIN+ – VIN–) • Gain Shutdown Copyright © 2000, Texas Instruments Incorporated V+ SBOS174A V– Printed in U.S.A. December, 2000 SPECIFICATIONS: VS = +2.7V TO +5.5V BOLDFACE limits apply over the specified temperature range, TA = –55°C TO 125°C At TA = +25°C, RL = 25kΩ, G = 25, and IA common = VS /2, unless otherwise noted. INA322EA INA2322EA PARAMETER INPUT Input Offset Voltage, RTI Over Temperature vs Temperature vs Power Supply Over Temperature Long-Term Stability Input Impedance Input Common-Mode Range Common-Mode Rejection Over Temperature CONDITION VOS dVOS/dT PSRR MIN TYP MAX UNITS VS = +5V ±2 VS = +2.7V to +5.5V ±7 ±50 ±10 ±11 mV mV µV/°C µV/V µV/V µV/month Ω || pF V V dB dB dB dB ±0.4 1013 || 3 CMRR VS = 2.7V VS = 5V VS = 5V, VCM = 0.55V to 3.8V VS = 5V, VCM = 0.55V to 3.8V VS = 2.7V, VCM = 0.35V to 1.5V 0.35 0.55 60 60 NOISE, RTI Voltage Noise: f = 10Hz f = 100Hz f = 1kHz f = 0.1Hz to 10Hz Current Noise: f = 1kHz Slew Rate Settling Time, 0.1% 0.01% Overload Recovery POWER SUPPLY Specified Voltage Range Operating Voltage Range Quiescent Current per Channel Over Temperature Shutdown Quiescent Current/Chan TEMPERATURE RANGE Specified Range Operating/Storage Range Thermal Resistance pA pA RS = 0Ω G>5 ±0.07 ±2 ±0.001 ±0.002 G=5 G = 25, VS = 5V, VO = 0.05 to 4.95 G ≥ 10 nV/√Hz nV/√Hz nV/√Hz µVp-p fA/√Hz G = 5 + 5(R2/R1) 5 OUTPUT Output Voltage Swing from Rail(2, 5) FREQUENCY RESPONSE Bandwidth, –3dB ±10 ±10 500 190 100 20 3 GAIN(1) Gain Equation, Externally Set Range of Gain Gain Error vs Temperature Nonlinearity Over Temperature Over Temperature Capacitance Load Drive Short-Circuit Current 73 ±0.5 ±0.5 IB IOS en 1.5 3.8 73 110 Crosstalk, Dual INPUT BIAS CURRENT Bias Current Offset Current ±250 ±260 50 1000 ±0.4 ±10 ±0.010 ±0.015 25 mV 50 mV pF See Typical Curve(3) 8 16 ISC– ISC+ V/V % ppm/°C % of FS % of FS mA BW G=5 500 kHz SR tS VS = 5V, G = 25 G = 5, CL = 50pF, VO = 2V step 0.4 8 12 2 V/µs µs µs µs 50% Input Overload G = 25 +2.7 +5.5 IQ VSD > 2.5(4) +2.5 to +5.5 40 ISD VSD < 0.8(4) 0.01 –55 –65 θJA MSOP-8, TSSOP-14 Surface Mount 60 70 1 +125 +150 150 V V µA µA µA °C °C °C/W NOTES: (1) Does not include errors from external gain setting resistors (2) Output voltage swings are measured between the output and power-supply rails. Output swings and rail only if G ≥ 10. (3) See typical performance curve “Percent Overshoot vs Load Capacitance.” (4) See typical performance curve “Shutdown Voltage vs Supply Voltage.” (5) Output does not swing to positive rail if gain is less than 10. 2 INA322 SBOS174 PIN CONFIGURATION Top View Top View INA2322 INA322 RGA 1 14 Shutdown A RG 1 8 Shutdown VIN–A 2 13 VOUTA VIN– 2 7 V+ VIN+A 3 12 REFA VIN+ 3 6 VOUT V– 4 11 V+ V– 4 5 REF VIN+B 5 10 REFB VIN–B 6 9 VOUTB RGB 7 8 Shutdown B MSOP-8 (EA) Dual, TSSOP-14 (EA) ABSOLUTE MAXIMUM RATINGS(1) ELECTROSTATIC DISCHARGE SENSITIVITY Supply Voltage, V+ to V– ................................................................... 7.5V Signal Input Terminals, Voltage(2) .................. (V–) – 0.5V to (V+) + 0.5V Current(2) .................................................... 10mA Output Short-Circuit(3) .............................................................. Continuous Operating Temperature .................................................. –65°C to +150°C Storage Temperature ..................................................... –65°C to +150°C Junction Temperature .................................................................... +150°C Lead Temperature (soldering, 10s) ............................................... +300°C This integrated circuit can be damaged by ESD. Burr-Brown 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. NOTE: (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. (3) Short-circuit to ground one amplifier per package. PACKAGE/ORDERING INFORMATION PRODUCT PACKAGE PACKAGE DRAWING NUMBER SINGLE INA322EA MSOP-8 337 –55°C to +125°C C22 " " " " TSSOP-14 357 –55°C to +125°C INA2322EA " " " " " DUAL INA2322EA " SPECIFIED TEMPERATURE RANGE PACKAGE MARKING ORDERING NUMBER(1) TRANSPORT MEDIA INA322EA/250 INA322EA/2K5 Tape and Reel Tape and Reel INA2322EA/250 INA2322EA/2K5 Tape and Reel Tape and Reel NOTES: (1) Models with a slash (/) are available only in Tape and Reel in the quantities indicated (e.g., /2K5 indicates 2500 devices per reel). Ordering 2500 pieces of “INA322E/2K5” will get a single 2500-piece Tape and Reel. INA322 SBOS174 3 TYPICAL PERFORMANCE CURVES At TA = +25°C, VS = 5V, VCM = 1/2 VS, RL = 25kΩ, CL = 50pF, unless otherwise noted. COMMON-MODE REJECTION RATIO vs FREQUENCY GAIN vs FREQUENCY 120 80 70 60 50 80 Gain = 100 CMRR (dB) Gain (dB) 100 Gain = 500 40 Gain = 25 30 20 Gain = 5 10 0 60 40 20 –10 –20 0 10 100 1k 10k 100k 1M 10 10M 100 POWER-SUPPLY REJECTION RATIO vs FREQUENCY Maximum Output Voltage (Vp-p) 90 80 70 PSRR (dB) 100k 10k MAXIMUM OUTPUT VOLTAGE vs FREQUENCY 6 100 60 50 40 30 20 10 0 VS = 5.5V 5 VS = 5.0V 4 VS = 2.7V 3 2 1 0 1 10 100 1k 10k 100 100k NOISE vs FREQUENCY 10 100 1 10 100 1k 100k 1M 10M 10k 0.1 100k 10µv/div 1k INoise (fA/√Hz) 100 10 10k 0.1Hz TO 10Hz VOLTAGE NOISE 10k 1 1k Frequency (Hz) Frequency (Hz) VNoise (nV/√Hz) 1k Frequency (Hz) Frequency (Hz) 1s/div Frequency (Hz) 4 INA322 SBOS174 TYPICAL PERFORMANCE CURVES (Cont.) At TA = +25°C, VS = 5V, VCM = 1/2 VS, RL = 25kΩ, CL = 50pF, unless otherwise noted. COMMON-MODE INPUT RANGE vs REFERENCE VOLTAGE OUTPUT SWING vs LOAD RESISTANCE 6 Output—Referred to Ground (V) 25 15 To Positive Rail 10 To Negative Rail 5 Outside of Normal Operation 4 3 REF Increasing 2 1 0 0 0 20k 40k 80k 60k 0 100k 2 4 3 5 RLoad (Ω) QUIESCENT CURRENT AND SHUTDOWN CURRENT vs POWER SUPPLY QUIESCENT CURRENT AND SHUTDOWN CURRENT vs TEMPERATURE 50 500 60 45 450 55 350 300 25 250 20 200 15 150 10 40 IQ (µA) 30 0 3 3.5 4 4.5 5 400 IQ 35 30 300 25 20 200 15 100 ISD 5 500 45 ISD (nA) 35 600 50 400 IQ 2.5 1 Input Common-Mode Voltage (V) 40 IQ (µA) 5 10 50 5 0 0 5.5 ISD –75 –50 –25 0 Supply Voltage (V) 25 50 75 100 125 100 0 150 Temperature (°C) SHORT-CIRCUIT CURRENT vs TEMPERATURE SHORT-CIRCUIT CURRENT vs POWER SUPPLY 20 30 25 ISC+ 15 10 ISC (mA) ISC (mA) 20 ISC– ISC+ 15 10 5 ISC– 5 0 0 2.5 3 3.5 4 4.5 Supply Voltage (V) INA322 SBOS174 5 5.5 –75 –50 –25 0 25 50 75 100 125 150 Temperature (°C) 5 ISD (nA) Swing to Rail (mV) 20 TYPICAL PERFORMANCE CURVES (Cont.) At TA = +25°C, VS = 5V, VCM = 1/2 VS, RL = 25kΩ, CL = 50pF, unless otherwise noted. 50µs/div SMALL-SIGNAL STEP RESPONSE (G = 5, CL = 1000pF) SMALL-SIGNAL STEP RESPONSE (G = 100, CL = 1000pF) 50mv/div 100mv/div 10µs/div 50µs/div SMALL-SIGNAL STEP RESPONSE (G = 100, CL = 5000pF) LARGE-SIGNAL STEP RESPONSE (G = 25, CL = 50pF) 1V/div 50mv/div 10µs/div 50µs/div 6 SMALL-SIGNAL STEP RESPONSE (G = 100) 50mv/div 100mv/div SMALL-SIGNAL STEP RESPONSE (G = 5) 50µs/div INA322 SBOS174 TYPICAL PERFORMANCE CURVES (Cont.) At TA = +25°C, VS = 5V, VCM = 1/2 VS, RL = 25kΩ, CL = 50pF, unless otherwise noted. SETTLING TIME vs GAIN PERCENT OVERSHOOT vs LOAD CAPACITANCE 100 60 Output 2Vp-p Differential Input Drive Settling Time (µs) 80 Output 100mVp-p Differential Input Drive 50 70 Overshoot (%) 90 0.01% 60 50 40 30 G=5 40 30 G = 25 20 0.1% 20 10 10 0 0 1 10 100 1000 10 100 1k Gain (V/V) Load Capacitance (pF) SHUTDOWN VOLTAGE vs SUPPLY VOLTAGE SHUTDOWN TRANSIENT BEHAVIOR 10k 3 Operation in this Region is not Recommended 2.5 VSD 2 1V/div Shutdown (V) Normal Operation Mode 1.5 1 VOUT Shutdown Mode 0.5 Part Draws Below 1µA Quiescent Current 0 2.3 3 3.5 4 4.5 5 50µs/div 5.5 Supply Voltage (V) OFFSET VOLTAGE DRIFT PRODUCTION DISTRIBUTION 20 18 18 Percentage of Amplifiers (%) 20 16 14 12 10 8 6 4 16 14 12 10 8 6 4 2 0 0 –20 –18 –16 –14 –12 –10 –8 –6 –4 –2 0 2 4 6 8 10 12 14 16 18 20 2 –10 –9 –8 –7 –6 –5 –4 –3 –2 –1 0 1 2 3 4 5 6 7 8 9 10 Percentage of Amplifiers (%) OFFSET VOLTAGE PRODUCTION DISTRIBUTION Offset Voltage (mV) Offset Voltage Drift (µV/°C) INA322 SBOS174 7 TYPICAL PERFORMANCE CURVES (Cont.) At TA = +25°C, VS = 5V, VCM = 1/2 VS, RL = 25kΩ, CL = 50pF, unless otherwise noted. INPUT BIAS CURRENT vs TEMPERATURE 10k 0.8 1k Input Bias Current (pA) SR (V/µs) SLEW RATE vs TEMPERATURE 1 0.6 0.4 0.2 0 100 10 0 0.1 –75 –50 –25 0 25 50 75 100 125 –75 150 –50 –25 0 CROSSTALK vs FREQUENCY 75 100 125 150 5 100 4 Output Voltage (V) Crosstalk (dB) 50 OUTPUT VOLTAGE SWING vs OUTPUT CURRENT 120 80 60 40 125°C 25°C –55°C 3 2 125°C 25°C –55°C 1 20 0 0 0.1 1 10 100 1k Frequency (Hz) 8 25 Temperature (°C) Temperature (°C) 10k 100k 1M 0 2 4 6 8 10 12 14 16 18 20 22 24 Output Current (mA) INA322 SBOS174 APPLICATIONS INFORMATION OPERATING VOLTAGE The INA322 family is fully specified and guaranteed over a supply range of +2.7V to +5.5V, with key parameters guaranteed over the temperature range of -55°C to +125°C. Parameters that vary significantly with operating conditions, such as load conditions or temperature, are shown in the Typical Performance Curves. The INA322 is a modified version of the classic “two op amp” instrumentation amplifier, with an additional gain amplifier. Figure 1 shows the basic connections for the operation of the INA322 and INA2322. The power supply should be capacitively decoupled with 0.1µF capacitors as close to the INA322 as possible for noisy or high-impedance applications. The output is referred to the reference terminal, which must be at least 1.2V below the positive supply rail. The INA322 may be operated on a single supply. Figure 2 shows a bridge amplifier circuit operated from a single +5V supply. The bridge provides a small differential voltage riding on an input common-mode voltage. G = 5 + 5(R2 / R1 ) Short VOUT to RG for G = 5 R1 DESIRED GAIN (V/V) R2 5 10 50 100 RG 1 REF VIN– VIN+ 5 160kΩ 40kΩ R2 R1 OPEN SHORT 100kΩ 100kΩ 10kΩ 90kΩ 10kΩ 190kΩ 160kΩ 40kΩ A1 2 A3 6 VO = ((VIN+) – (VIN –)) • G A2 3 Also drawn in simplified form: 8 4 7 Shutdown VIN+ (For Single Supply) 0.1µF V+ 7 5 INA322 0.1µF 8 REF V– V+ Shutdown 3 VIN– 2 6 VOUT 1 4 V– RG FIGURE 1. Basic Connections. +5V Bridge Sensor VIN+ 3 V+ 7 REF(1) 5 INA322 Shutdown 8 VIN– 6 VOUT 1 2 4 V– RG NOTE: (1) REF should be adjusted for the desired output level, keeping in mind that the value of REF affects the common-mode input range. See Typical Performance Curves. FIGURE 2. Bridge Amplifier of the INA322. INA322 SBOS174 9 SETTING THE GAIN The ratio of R2 to R1, or the impedance between pins 1, 5, and 6, determines the gain of the INA322. With an internally set gain of 5, the INA322 can be programmed for gains greater than 5 according to the following equation: G = 5 + 5(R2/R1) V+ VIN+ 3 8 Microphone, Hydrophone, etc. REF 47kΩ VB (See Typical Performance Curves for Input Common-Mode Range vs Reference Voltage). REFERENCE The reference terminal defines the zero output voltage level. In setting the reference voltage, the common mode input of A3 should be considered according to the following equation: VOA2 = VREF + 5(VIN+ – VIN–) For guaranteed operation, VOA2 should be less than VDD – 1.2V. The reference pin requires a low-impedance connection. Any resistance in series with the reference pin will degrade the CMRR. The reference pin may be used to compensate for the offset voltage (see Offset Trimming section). The reference voltage level also influences the common-mode input range (see Common-Mode Input Range section). INPUT BIAS CURRENT RETURN With a high input impedance of 1013Ω, the INA322 is ideal for use with high-impedance sources. The input bias current of less than 10pA makes the INA322 nearly independent of input impedance and ideal for low-power applications. For proper operation, a path must be provided for input bias currents for both inputs. Without input bias current paths, 10 INA322 VOUT 4 V– RG (1) VIN+ 3 Shutdown 7 8 Transformer 6 1 V+ INPUT COMMON-MODE RANGE VOA1 = 5/4 VCM – 1/4 VREF 5 VIN– 2 The INA322 is designed to provide accurate gain, with gain error guaranteed to be less than 0.4%. Setting gain with matching TC resistors will minimize gain drift. Errors from external resistors will add directly to the guaranteed error, and may become dominant error sources. The upper limit of the common mode input range is set by the common-mode input range of the second amplifier, A2, to 1.2V below positive supply. Under most conditions, the amplifier operates beyond this point with reduced performance. The lower limit of the input range is bounded by the output swing of amplifier A1, and is a function of the reference voltage according to the following equation: Shutdown 7 REF 5 INA322 6 VOUT 1 VIN– 2 4 VB(1) Bridge Amplifier V– Center-tap RG provides bias current return VEX V+ Bridge Sensor VIN+ 3 Shutdown 7 8 REF 5 INA322 6 VOUT 1 VIN– 2 4 V– RG Bridge resistance provides bias current return NOTE: (1) VB is bias voltage within common-mode range, dependent on REF. FIGURE 3. Providing an Input Common-Mode Path. the inputs will “float” to a potential that exceeds commonmode range and the input amplifier will saturate. Figure 3 shows how bias current path can be provided in the cases of microphone applications, thermistor applications, ground returns, and dc-coupled resistive bridge applications. When differential source impedance is low, the bias current return path can be connected to one input. With higher source impedance, two equal resistors will provide a balanced input. The advantages are lower input offset voltage due to bias current flowing through the source impedance and better high-frequency gain. INA322 SBOS174 OUTPUT BUFFERING +5V The INA322 is optimized for a load impedance of 10kΩ or greater. For higher output current the INA322 can be buffered using the OPA340, as shown in Figure 4. The OPA340 can swing within 50mV of the supply rail, driving a 600Ω load. The OPA340 is available in the tiny MSOP-8 package. 0.1µF VIN+ 3 V+ 7 5 INA322 8 REF VIN– 0.1µF Shutdown 6 VOUT 1 2 OFFSET TRIMMING VOUT OPA340 4 RG FIGURE 4. Output Buffering Circuit. Able to drive loads as low as 600Ω. In the event that external offset adjustment is required, the offset can be adjusted by applying a correction voltage to the reference terminal. Figure 6 shows an optional circuit for trimming offset voltage. The voltage applied to the REF terminal is added to the output signal. The gain from REF to VOUT is +1. An op-amp buffer is used to provide low impedance at the REF terminal to preserve good commonmode rejection. SHUTDOWN MODE The shutdown pin of the INA322 is nominally connected to V+. When the pin is pulled below 0.8V on a 5V supply, the INA322 goes into sleep mode within nanoseconds. For actual shutdown threshold, see typical performance curve “Shutdown Voltage vs Supply Voltage”. Drawing less than 1µA of current, and returning from sleep mode in microseconds, the shutdown feature is useful for portable applications. Once in ‘sleep-mode’ the amplifier has high output impedance, making the INA322 suitable for multiplexing. V+ VIN+ +5V V+ 7 5 INA322 VIN– 2 1 4 V– INA322 2 VIN– 6 VOUT ADS7818 or ADS7822 V– RG Adjustable Voltage NOTE: (1) REF should be adjusted for the desired output level. The value of REF affects the common-mode input range. FIGURE 6. Optional Offset Trimming Voltage. INPUT PROTECTION Device inputs are protected by ESD diodes that will conduct if the input voltages exceed the power supplies by more than 500mV. Momentary voltages greater than 500mV beyond the power supply can be tolerated if the current through the input pins is limited to 10mA. This is easily accomplished with input resistor RLIM, as shown in Figure 7. Many input signals are inherently current-limited to less than 10mA, therefore, a limiting resistor is not required. V+ 12-Bits RLIM 3 VIN+ IOVERLOAD 10mA max RG fS < 100kHz FIGURE 5. INA322 Directly Drives a Capacitive-Input, A/D Converter. SBOS174 VOUT 4 REF 5 Shutdown 7 8 INA322 6 VOUT 1 2 VIN– INA322 6 1 Shutdown 8 REF 5 OPA336 A class AB output stage with common-source transistors is used to achieve rail-to-rail output for gains of 10 or greater. When the amplifier is in G = 5 the output will not swing to positive rail. For resistive loads greater than 25kΩ, the output voltage can swing to within a few millivolts of the supply rail while maintaining low gain error. For heavier loads and over temperature, see the typical performance curve “Output Voltage Swing vs Output Current.” The INA322’s low output impedance at high frequencies makes it suitable for directly driving Capacitive Digital-to-Analog (CDAC) input A/D converters, as shown in Figure 5. 3 7 8 REF(1) RAIL TO RAIL OUTPUT VIN+ Shutdown 3 4 RLIM V– RG FIGURE 7. Input Protection. 11 OFFSET VOLTAGE ERROR CALCULATION FEEDBACK CAPACITOR IMPROVES RESPONSE The offset voltage (VOS) of the INA322EA has a specified maximum of 10mV with a +5V power supply and the common-mode voltage at VS/2. Additional specifications for power-supply rejection and common-mode rejection are provided to allow the user to easily calculate worst-case expected offset under the conditions of a given application. Power Supply Rejection Ratio (PSRR) is specified in µV/V. For the INA322, worst case PSRR is 250µV/V, which means for each volt of change in power supply, the offset may shift up to 250µV. Common-Mode Rejection Ratio (CMRR) is specified in dB, which can be converted to µV/V using the following equation: For optimum settling time and stability with high-impedance feedback networks, it may be necessary to add a feedback capacitor across the feedback resistor, RF, as shown in Figure 8. This capacitor compensates for the zero created by the feedback network impedance and the INA322’s RGpin input capacitance (and any parasitic layout capacitance). The effect becomes more significant with higher impedance networks. Also, RX and CL can be added to reduce highfrequency noise. CMRR (in µV/V) = 10[(CMRR in dB)/–20] • 106 V+ VIN+ 7 3 Shutdown 8 INA322 For the INA322, the worst case CMRR over the specified common-mode range is 60dB (at G = 25) or about 1mV/V This means that for every volt of change in common-mode, the offset will shift less than 1mV. These numbers can be used to calculate excursions from the specified offset voltage under different application conditions. For example, an application might configure the amplifier with a 3.3V supply with 1V common-mode. This configuration varies from the specified configuration, representing a 1.7V variation in power supply (5V in the offset specification versus 3.3V in the application) and a 0.65V variation in common-mode voltage from the specified VS/2. Calculation of the worst-case expected offset would be as follows: Adjusted VOS = Maximum specified VOS + (power-supply variation) • PSRR + (common-mode variation) • CMRR VOS = 10mV + (1.7V • 0.250mV/V) + (0.65V • 1mV/V) = ±11.075mV However, the typical value will be closer to 2.2mV (calculated using the typical values). 12 REF 6 5 VOUT CIN CL 1 VIN– RX 2 4 RG V– RIN RF RIN • CIN = RF • CF CF Where CIN is equal to the INA322’s input capacitance (approximately 3pF) plus any parastic layout capacitance. FIGURE 8. Feedback Capacitor Improves Dynamic Performance. It is suggested that a variable capacitor be used for the feedback capacitor since input capacitance may vary between instrumentation amplifiers, and layout capacitance is difficult to determine. For the circuit shown in Figure 8, the value of the variable feedback capacitor should be chosen by the following equation: RIN • CIN = RF • CF Where CIN is equal to the INA322’s RG-pin input capacitance (typically 3pF) plus the layout capacitance. The capacitor can be varied until optimum performance is obtained. INA322 SBOS174 APPLICATION CIRCUITS drive. Filtering can be modified to suit application needs by changing the capacitor value of the output filter. Low-Power, Single-Supply Data Acquisition Systems Refer to Figure 5 to see the INA322 configured to drive an ADS7818. Functioning at frequencies of up to 500kHz, the INA322 is ideal for low-power data acquisition. Medical ECG Applications Figure 9 shows the INA322 configured to serve as a lowcost ECG amplifier, suitable for moderate accuracy heartrate applications such as fitness equipment. The input signals are obtained from the left and right arms of the patient. The common-mode voltage is set by two 2MΩ resistors. This potential through a buffer, provides optional right leg VR OPA336 1.6nF 0.1µF V+ 100kΩ VIN+ 3 Left Arm 100kΩ Right Arm Shutdown 7 8 REF 5 VIN– 2 INA322 1 V– 2MΩ 10kΩ 6 10kΩ OPA336 VOUT PUT VR 4 +5V 1MΩ 1MΩ RG 1MΩ 2MΩ 2kΩ VR = +2.5V 2kΩ OPA336 Right Leg FIGURE 9. Simplified ECG Circuit for Medical Applications. INA322 SBOS174 13 PACKAGE OPTION ADDENDUM www.ti.com 30-Mar-2005 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Drawing Pins Package Eco Plan (2) Qty Lead/Ball Finish MSL Peak Temp (3) INA2322EA/250 ACTIVE TSSOP PW 14 250 TBD CU NIPDAU Level-3-220C-168 HR INA2322EA/2K5 ACTIVE TSSOP PW 14 2500 TBD CU NIPDAU Level-3-220C-168 HR INA322EA/250 ACTIVE MSOP DGK 8 250 TBD CU NIPDAU Level-3-260C-168 HR INA322EA/2K5 ACTIVE MSOP DGK 8 2500 TBD CU NIPDAU Level-3-260C-168 HR (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. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS) or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. 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