Precision INSTRUMENTATION AMPLIFIER

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1 Precision INSTRUMENTATION AMPLIFIER FEATURES LOW OFFSET VOLTAGE: µv max LOW DRIFT:.µV/ C max LOW INPUT BIAS CURRENT: na max HIGH COMMON-MODE REJECTION: db min INPUT OVER-VOLTAGE PROTECTION: ±V WIDE SUPPLY RANGE: ±. TO ±V LOW QUIESCENT CURRENT: ma max SOL- SURFACE-MOUNT PACKAGE APPLICATIONS SWITCHED-GAIN AMPLIFIER BRIDGE AMPLIFIER THERMOCOUPLE AMPLIFIER RTD SENSOR AMPLIFIER MEDICAL INSTRUMENTATION DATA ACQUISITION DESCRIPTION The is a low cost, general purpose instrumentation amplifier offering excellent accuracy. Its versatile three-op amp design and small size make it ideal for a wide range of applications. Similar to the model INA, the provides additional connections to the input op amps, A and A, which improve gain accuracy in high gains and are useful in forming switched-gain amplifiers. A single external resistor sets any gain from to,. Internal input protection can withstand up to ±V without damage. The is laser trimmed for very low offset voltage (µv), drift (.µv/ C) and high commonmode rejection (db at G=). It operates with power supplies as low as ±.V, allowing use in battery operated and single V supply systems. Quiescent current is ma maximum. The is available in the SOL- surface-mount package, specified for the C to C temperature range. V A Feedback A G = kω A Ref V International Airport Industrial Park Mailing Address: PO Box, Tucson, AZ Street Address: S. Tucson Blvd., Tucson, AZ Tel: () - Twx: 9-9- Internet: FAXLine: () - (US/Canada Only) Cable: BBRCORP Telex: -9 FAX: () 9- Immediate Product Info: () - 99 Burr-Brown Corporation PDS-9B Printed in U.S.A. October, 99

2 SPECIFICATIONS ELECTRICAL At T A = C, V S = ±V, R L = kω unless otherwise noted. BU AU PARAMETER CONDITIONS MIN TYP MAX MIN TYP MAX UNITS INPUT Offset Voltage, RTI Initial T A = C ± /G ± /G ± /G ± /G µv vs Temperature T A = T MIN to T MAX ±../G ±. /G ±. /G ± /G µv/ C vs Power Supply V S = ±.V to ±V. /G /G µv/v Long-Term Stability ±../G µv/mo Impedance, Differential Ω pf Common-Mode Ω pf Input Common-Mode Range ± ±. V Safe Input Voltage ± V Common-Mode Rejection V CM = ±V, R S = kω G = 9 9 db G = 9 9 db G = db G = db BIAS CURRENT ±. ± ± na vs Temperature ± pa/ C OFFSET CURRENT ±. ± ± na vs Temperature ± pa/ C NOISE VOLTAGE, RTI G =, R S = Ω f = Hz nv/ Hz f = Hz nv/ Hz f = khz nv/ Hz f B =.Hz to Hz. µvp-p Noise Current f=hz. pa/ Hz f=khz. pa/ Hz f B =.Hz to Hz pap-p GAIN Gain Equation (kω/ ) V/V Range of Gain V/V Gain Error G = ±. ±. % G = ±. ±. ±. % G = ±. ±. ±. % G = ±. ± ± % Gain vs Temperature G = ± ± ± ppm/ C kω Resistance () ± ± ppm/ C Nonlinearity G = ±. ±. ±. % of FSR G = ±. ±. ±. % of FSR G = ±. ±. ±. % of FSR G = ±. ±. ±. % of FSR OUTPUT () Voltage I O = ma, T MIN to T MAX ±. ±. V V S = ±.V, R L = kω ± ±. V V S = ±.V, R L = kω ± ±. V Load Capacitance Stability pf Short Circuit Current / ma FREQUENCY RESPONSE Bandwidth, db G = MHz G = khz G = khz G = khz Slew Rate = ±V, G =.. V/µs Settling Time,.% G = µs G = µs G = µs G = µs Overload Recovery % Overdrive µs POWER SUPPLY Voltage Range ±. ± ± V Current = V ±. ± ma TEMPERATURE RANGE Specification C Operating C θ JA C/W Specification same as BU. NOTE: () Temperature coefficient of the kω term in the gain equation. () Output specifications are for output amplifier, A. A and A provide the same output voltage swing but have less output current drive. A and A can drive external loads of pf.

3 PIN CONFIGURATIONS Gain Sense U Package V IN V IN SOL- Surface-Mount Top View NC V Gain Sense Feedback ELECTROSTATIC DISCHARGE SENSITIVITY 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. NC V Ref ABSOLUTE MAXIMUM RATINGS 9 NC Supply Voltage... ±V Input Voltage Range... ±V Output Short-Circuit (to ground)... Continuous Operating Temperature... C to C Storage Temperature... C to C Junction Temperature... C Lead Temperature (soldering, s)... C PACKAGE/ORDERING INFORMATION PACKAGE DRAWING TEMPERATURE PRODUCT PACKAGE NUMBER () RANGE AU SOL- Surface-Mount C to C BU SOL- Surface-Mount C to C NOTE: () For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book. The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support devices and/or systems.

4 TYPICAL PERFORMANCE CURVES At T A = C, V S = ±V, unless otherwise noted. Gain (V/V) k GAIN vs FREQUENCY connected to Gain Sense and connected to Gain Sense. See text. k k k M Common-Mode Rejection (db) COMMON-MODE REJECTION vs FREQUENCY G =, k G = G = k G = G = G = k k k M Common-Mode Voltage (V) INPUT COMMON-MODE VOLTAGE RANGE vs OUTPUT VOLTAGE Limited by A Output Swing V D/ V D/ V CM (Any Gain) A Output Swing Limit Limited by A Output Swing Output Voltage (V) Limited by A Output Swing A Output Swing Limit Limited by A Output Swing Power Supply Rejection (db) POSITIVE POWER SUPPLY REJECTION vs FREQUENCY k k k M G = G = G = G = Power Supply Rejection (db) NEGATIVE POWER SUPPLY REJECTION vs FREQUENCY G = G = G = k k k M G = Input-Referred Noise Voltage (nv/ Hz) k INPUT- REFERRED NOISE VOLTAGE vs FREQUENCY G =, k G = G = G = BW Limit k

5 TYPICAL PERFORMANCE CURVES (CONT) At T A = C, V S = ±V, unless otherwise noted. SETTLING TIME vs GAIN OFFSET VOLTAGE WARM-UP vs TIME Settling Time (µs).%.% Offset Voltage Change (µv) G > Gain (V/V) 9 Time from Power Supply Turn-on (s) Input Bias and Input Offset Current (na) ±I B INPUT BIAS AND INPUT OFFSET CURRENT vs TEMPERATURE I OS Input Bias Current (ma) INPUT BIAS CURRENT vs DIFFERENTIAL INPUT VOLTAGE G = G = G = G = Differential Overload Voltage (V) Input Bias Current (ma) One Input INPUT BIAS CURRENT vs COMMON-MODE INPUT VOLTAGE Normal Operation I b I b Both Inputs One Input Both Inputs Common-Mode Voltage (V) Peak to Peak Amplitude (V) MAXIMUM OUTPUT SWING vs FREQUENCY G =, G = G = k k k M

6 TYPICAL PERFORMANCE CURVES (CONT) At T A = C, V S = ±V, unless otherwise noted.. SLEW RATE vs TEMPERATURE OUTPUT CURRENT LIMIT vs TEMPERATURE Slew Rate (V/µs).... Short Circuit Current (ma) I CL I CL. QUIESCENT CURRENT vs TEMPERATURE. QUIESCENT CURRENT AND POWER DISSIPATION vs POWER SUPPLY VOLTAGE Quiescent Current (ma).... Quiescent Current (ma)..... Power Dissipation Quiescent Current Power Dissipation (mw).. ± ± ±9 ± ± ± Power Supply Voltage (V) POSITIVE SIGNAL SWING vs TEMPERATURE (R L = kω) V S = ±V NEGATIVE SIGNAL SWING vs TEMPERATURE (R L = kω) V S = ±V Output Voltage (V) V S = ±.V V S = ±.V Output Voltage (V) V S = ±.V V S = ±.V

7 TYPICAL PERFORMANCE CURVES (CONT) At T A = C, V S = ±V, unless otherwise noted. LARGE SIGNAL RESPONSE, G = SMALL SIGNAL RESPONSE, G = V mv V mv connected to Gain Sense and connected to Gain Sense LARGE SIGNAL RESPONSE, G = SMALL SIGNAL RESPONSE, G = V mv V mv INPUT-REFERRED NOISE,. to Hz.µV/div s/div

8 APPLICATION INFORMATION Figure shows the basic connections required for operation of the. Applications with noisy or high impedance power supplies may require decoupling capacitors close to the device pins as shown. The output is referred to the output reference (Ref) terminal which is normally grounded. This must be a low-impedance connection to assure good common-mode rejection. A resistance of Ω in series with the Ref pin will cause a typical device to degrade to approximately db CMR (G=). The has a separate output sense feedback connection (pin ). Pin must be connected (normally to the output terminal, pin ) for proper operation. The output sense connection can be used to sense the output voltage directly at the load for best accuracy. SETTING THE GAIN Gain of the is set by connecting a single external resistor, : G = kω () Commonly used gains and resistor values are shown in Figure. For G=, no resistor is required, but connect pins - and connect pins -. Gain peaking in G= can be reduced by shorting the internal feedback resistors (see typical performance curve Gain vs Frequency). To do this, connect pins -- and connect pins --. The kω term in equation comes from the sum of the two internal feedback resistors. These are on-chip metal film resistors which are laser trimmed to accurate absolute values. The accuracy and temperature coefficient of these resistors are included in the gain accuracy and drift specifications of the. The stability and temperature drift of the external gain setting resistor,, also affects gain. s contribution to gain error and drift can be directly inferred from the gain equation (). Low resistor values required for high gain can make wiring resistance important. The force and sense type connections illustrated in Figure help reduce the effect of interconnection resistance. V.µF A = G ( ) G = kω A Load A.µF DESIRED NEAREST % GAIN (Ω) (Ω) No Connection No Connection.k 9.9k.k.k.k.k.k.k.k.k V Also drawn in simplified form: R G Ref FIGURE. Basic Connections.

9 SWITCHED GAIN Figure shows a circuit for digital selection of four gains. Multiplexer on resistance does not significantly affect gain. The resistor values required for some commonly used gain steps are shown. This circuit uses the internal feedback resistors, so the resistor values shown cannot be scaled to a different impedance level. Figure shows an alternative switchable gain configuration. This circuit does not use the internal feedback resistors, so the nominal values shown can be scaled to other impedance levels. This circuit is ideal for use with a precision resistor network to achieve excellent gain accuracy and lowest gain drift. NOISE PERFORMANCE The provides very low noise in most applications. For differential source impedances less than kω, the INA may provide lower noise. For source impedances greater than kω, the INA FET-Input Instrumentation Amplifier may provide lower noise. Low frequency noise of the is approximately.µvp-p measured from. to Hz. This is approximately one-tenth the noise of low noise chopper-stabilized amplifiers. OFFSET TRIMMING The is laser trimmed for very low offset voltage and drift. Most applications require no external offset adjustment. Figure shows an optional circuit for trimming the output offset voltage. The voltage applied to Ref terminal is summed at the output. Low impedance must be maintained at this node to assure good common-mode rejection. This is achieved by buffering the trim voltage with an op amp as shown. INPUT BIAS CURRENT RETURN PATH The input impedance of the is extremely high approximately Ω. However, a path must be provided for the input bias current of both inputs. This input bias current is typically less than ±na (it can be either polarity due to cancellation circuitry). 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 if the is to operate properly. Figure shows various provisions for an input bias current path. Without a bias current return path, the inputs will float to a potential which exceeds the common-mode range of the and the input amplifiers will saturate. If the differential source resistance is low, a bias current return path can be connected to one input (see thermocouple example in Figure ). With higher source impedance, using two resistors provides a balanced input with possible advantages of lower input offset voltage due bias current and better common-mode rejection. V 9 Enable A A R R R A A Feedback R A HI-9 V A A Gain L L H L L H H H Highest R R R R GAIN STEPS (Ω) (Ω) (Ω) (Ω),,,.k..k,,,.k.k.k.k,,, k k k k,,, 9dB.k.k k.k FIGURE. Switched-Gain Instrumentation Amplifier (minimum components). 9

10 V 9 Enable A A R R R R R NC NC A A Feedback HI-9 R R A V A A Gain L L H L L H H H Highest R R R R R R R GAIN STEPS (Ω) (Ω) (Ω) (Ω) (Ω) (Ω) (Ω),,, V/V k.k.k k,,, V/V k 9k.k 9k.k 9k k,,, V/V k.k.k.k.k.k k,,, 9dB k.k 9.k.k 9.k.k k FIGURE. Switched-Gain Instrumentation Amplifier (improved gain drift). Ref V µa / REF Microphone, Hydrophone etc. kω kω OPA ±mv Adjustment Range kω Ω Ω Thermocouple µa / REF V kω FIGURE. Optional Trimming of Output Offset Voltage. Center-tap provides bias current return. FIGURE. Providing an Input Common-Mode Current Path.

11 INPUT COMMON-MODE RANGE The linear common-mode range of the input op amps of the is approximately ±.V (or.v from the power supplies). As the output voltage increases, however, the linear input range will be limited by the output voltage swing of the input amplifiers, A and A. The common-mode range is related to the output voltage of the complete amplifier see performance curve Input Common-Mode Range vs Output Voltage. A combination of common-mode and differential input signals can cause the output of A or A to saturate. Figure shows the output voltage swing of A and A expressed in terms of a common-mode and differential input voltages. Output swing capability of the input amplifiers, A and A is the same as the output amplifier, A. For applications where input common-mode range must be maximized, limit the output voltage swing by connecting the in a lower gain (see performance curve Input Common-Mode Voltage Range vs Output Voltage ). If necessary, add gain after the to increase the voltage swing. Input-overload often produces an output voltage that appears normal. For example, an input voltage of V on one input and V on the other input will obviously exceed the linear common-mode range of both input amplifiers. Since both input amplifiers are saturated to the nearly the same output voltage limit, the difference voltage measured by the output amplifier will be near zero. The output of the will be near V even though both inputs are overloaded. INPUT PROTECTION The inputs of the are individually protected for voltages up to ±V. For example, a condition of V on one input and V on the other input will not cause damage. Internal circuitry on each input provides low series impedance under normal signal conditions. To provide equivalent protection, series input resistors would contribute excessive noise. If the input is overloaded, the protection circuitry limits the input current to a safe value (approximately.ma). The typical performance curve Input Bias Current vs Common-Mode Input Voltage shows this input current limit behavior. The inputs are protected even if the power supply voltage is zero. OTHER APPLICATIONS See the INA data sheet for other applications circuits of general interest. V CM G V D V V D A G = kω A = G V D V D V CM A V CM G V D V FIGURE. Voltage Swing of A and A. RA LA 9kΩ RL 9kΩ OPA.9kΩ.9kΩ FIGURE. ECG Amplifier with Right Leg Drive.

Precision, Low Power INSTRUMENTATION AMPLIFIER

Precision, Low Power INSTRUMENTATION AMPLIFIER FEATURES LOW OFFSET VOLTAGE: µv max LOW DRIFT:.µV/ C max LOW INPUT BIAS CURRENT: na max HIGH CMR: db min INPUTS PROTECTED TO ±V WIDE SUPPLY RANGE: ±. to ±V