Precision, Low Power INSTRUMENTATION AMPLIFIER

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1 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 LOW QUIESCENT CURRENT: µa -PIN PLASTIC DIP, SO- APPLICATIONS BRIDGE AMPLIFIER THERMOCOUPLE AMPLIFIER RTD SENSOR AMPLIFIER MEDICAL INSTRUMENTATION DATA ACQUISITION DESCRIPTION The is a low power, general purpose instrumentation amplifier offering excellent accuracy. Its versatile -op amp design and small size make it ideal for a wide range of applications. Current-feedback input circuitry provides wide bandwidth even at high gain (7kHz at G = ). 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 common-mode rejection (db at G = ). It operates with power supplies as low as ±.V, and quiescent current is only µa ideal for battery operated systems. The is available in -pin plastic DIP, and SO- surface-mount packages, specified for the C to C temperature range. V 7 Over-Voltage Protection A kω kω kω G = kω A kω Over-Voltage Protection A kω kω V International Airport Industrial Park Mailing Address: PO Box, Tucson, AZ 7 Street Address: 7 S. Tucson Blvd., Tucson, AZ 7 Tel: () 7- Twx: 9-9- Internet: FAXLine: () - (US/Canada Only) Cable: BBRCORP Telex: -9 FAX: () 9- Immediate Product Info: () - 99 Burr-Brown Corporation PDS-99D Printed in U.S.A. April, 99

2 SPECIFICATIONS ELECTRICAL At T A = C, V S = ±V, R L = kω unless otherwise noted. PB, UB P, U 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 ± ±/G µv/v Long-Term Stability ±. ±/G µv/mo Impedance, Differential Ω pf Common-Mode Ω pf Linear Input Voltage Range (V) (V). V (V). (V).9 V Safe Input Voltage ± V Common-Mode Rejection V CM = ±V, R S = kω G = 9 7 db G = 97 9 db G = 7 9 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 = ±. ±. ±.7 % 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: Positive R L = kω (V) (V). V Negative R L = kω (V). (V). V Single Supply High V S =.7V/V (), R L = kω.. V Single Supply Low V S =.7V/V (), R L = kω mv Load Capacitance Stability pf Short Circuit Current / ma FREQUENCY RESPONSE Bandwidth, db G = khz G = khz G = 7 khz G = 7 khz Slew Rate = ±V, G =.9 V/µs Settling Time,.% G = µs G = µs G = µs G = µs Overload Recovery % Overdrive µs POWER SUPPLY Voltage Range ±. ± ± V Current = V ± ± µa TEMPERATURE RANGE Specification C Operating C θ JA C/W Specification same as PB, UB. NOTE: () Temperature coefficient of the kω term in the gain equation. () Common-mode input voltage range is limited. See text for discussion of low power supply and single power supply operation.

3 PIN CONFIGURATION -Pin DIP and SO- ELECTROSTATIC DISCHARGE SENSITIVITY V IN V IN V Top View 7 V 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. ABSOLUTE MAXIMUM RATINGS ORDERING INFORMATION Supply Voltage... ±V Analog 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 DRAWING TEMPERATURE PRODUCT PACKAGE NUMBER () RANGE P -Pin Plastic DIP C to C PB -Pin Plastic DIP C to C U SO- Surface-Mount C to C UB SO- 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 (db) G = G = G = G = GAIN vs FREQUENCY Common-Mode Rejection (db) COMMON-MODE REJECTION vs FREQUENCY G= G= G= G= k k k M M k k k Common-Mode Voltage (V) INPUT COMMON-MODE RANGE vs OUTPUT VOLTAGE G G G = G = V D/ V D/ V CM V V All All Gains Gains Output Voltage (V) Common-Mode Voltage (V) INPUT COMMON-MODE RANGE vs OUTPUT VOLTAGE G G All Gains G = G = V D/ V D/ V CM Output Voltage (V) V V All Gains INPUT COMMON-MODE RANGE vs OUTPUT VOLTAGE INPUT COMMON-MODE RANGE vs OUTPUT VOLTAGE Common-Mode Voltage (V) G = G = V D/ V D/ G Single Supply V Common-Mode Voltage (V) G = G Single Supply V V D/ V D/ V CM V CM Output Voltage (V) Output Voltage (V)

5 TYPICAL PERFORMANCE CURVES (CONT) At T A = C, V S = ±V, unless otherwise noted. POSITIVE POWER SUPPLY REJECTION vs FREQUENCY NEGATIVE POWER SUPPLY REJECTION vs FREQUENCY Power Supply Rejection (db) G = G = G = G = Power Supply Rejection (db) G = G = G = G = k k k k k k Input-erred Noise Voltage (nv/ Hz) k INPUT- REFERRED NOISE VOLTAGE vs FREQUENCY G = G = G =, G = BW Limit k Current Noise (All Gains). k Input Bias Current Noise (pa/ Hz) Settling Time (µs) SETTLING TIME vs GAIN R L = kω C L = pf Gain (V/V).%.% Quiescent Current (µa) QUIESCENT CURRENT and SLEW RATE vs TEMPERATURE 7 7 Temperature ( C) Slew Rate I Q V S = ±V V S = ±.V.. Slew Rate (V/µs) Input Bias Current (ma) INPUT BIAS CURRENT vs INPUT OVERLOAD VOLTAGE G = G = G = G = Overload Voltage (V)

6 TYPICAL PERFORMANCE CURVES (CONT) At T A = C, V S = ±V, unless otherwise noted. Offset Voltage Change (µv) OFFSET VOLTAGE vs WARM-UP TIME G = Time from Power Supply Turn On (ms) Input Bias and Offset Current (na) INPUT BIAS AND OFFSET CURRENT vs TEMPERATURE I OS ±I b 7 7 Temperature ( C) Output Voltage Swing (V) V (V). (V). (V). (V). OUTPUT VOLTAGE SWING vs OUTPUT CURRENT Positive Single Power Supply, V = V Ground-erred Load V S ±V V S = ±V Negative V Output Current (ma) Output Voltage Swing (V) OUTPUT VOLTAGE SWING vs POWER SUPPLY VOLTAGE V (V). Positive (V). C C (V). (V). (V) C R L = kω (V). C Negative C (V). C V ± ± ± ± Power Supply Voltage (V) OUTPUT CURRENT LIMIT vs TEMPERATURE MAXIMUM OUTPUT SWING vs FREQUENCY G =, Short Circuit Current (ma) I CL I CL Peak-to-Peak Output Voltage (V) G = G = 7 7 Temperature ( C) k k k M

k k k s/div SMALL-SIGNAL RESPONSE SMALL-SIGNAL RESPONSE G = G

7 TYPICAL PERFORMANCE CURVES (CONT) At T A = C, V S = ±V, unless otherwise noted. THD N vs FREQUENCY INPUT-REFERRED NOISE,.Hz to Hz G = THD N (%).. R L = kω.µv/div (Noise Floor) R L =. k k k s/div SMALL-SIGNAL RESPONSE SMALL-SIGNAL RESPONSE G = G = mv/div mv/div G = G = µs/div µs/div LARGE-SIGNAL RESPONSE LARGE-SIGNAL RESPONSE G = G = V/div V/div G = G = µs/div µs/div 7

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 () 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 pin will cause a typical device to degrade to approximately db CMR (G = ). SETTING THE GAIN Gain of the is set by connecting a single external resistor,, connected between pins and : G = kω Commonly used gains and resistor values are shown in Figure. The kω term in Equation comes from the sum of the two internal feedback resistors of A and A. These on-chip metal film resistors 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 accuracy and drift can be directly inferred from the gain equation (). Low resistor values required for high gain can make wiring resistance important. Sockets add to the wiring resistance which will contribute additional gain error (possibly an unstable gain error) in gains of approximately or greater. DYNAMIC PERFORMANCE The typical performance curve Gain vs Frequency shows that, despite its low quiescent current, the achieves wide bandwidth, even at high gain. This is due to the current-feedback topology of the. Settling time also remains excellent at high gain. The exhibits approximately db peaking at khz in unity gain. This is a result of its current-feedback topology and is not an indication of instability. Unlike an op amp with poor phase margin, the rise in response is a predictable db/octave due to a response zero. A simple pole at khz or lower will produce a flat passband unity gain response. V.µF 7 DESIRED NEAREST % GAIN (Ω) (Ω) NC NC.k 9.9k.k.k.k.k.k.k.k.k Over-Voltage Protection Over-Voltage Protection A kω kω A kω kω.µf kω A kω = G ( ) G = kω Load NC: No Connection. Also drawn in simplified form: V FIGURE. Basic Connections.

9 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 (G ). This provides dramatically improved noise when compared to stateof-the-art chopper-stabilized amplifiers. Microphone, Hydrophone etc. 7kΩ 7kΩ OFFSET TRIMMING The is laser trimmed for 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 terminal is summed at the output. The op amp buffer provides low impedance at the terminal to preserve good commonmode rejection. Thermocouple kω V µa / REF Center-tap provides bias current return. FIGURE. Providing an Input Common-Mode Current Path. OPA77 ±mv Adjustment Range kω Ω Ω µa / REF FIGURE. Optional Trimming of Output Offset Voltage. 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 approximately ±na. 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 shows various provisions for an input bias current path. Without a bias current path, the inputs will float to a potential which exceeds the commonmode range of the and the input amplifiers will saturate. If the differential source resistance is low, the bias current return path can be connected to one input (see the thermocouple example in Figure ). With higher source impedance, using two equal resistors provides a balanced input with possible advantages of lower input offset voltage due to bias current and better high-frequency common-mode rejection. V INPUT COMMON-MODE RANGE The linear input voltage range of the input circuitry of the is from approximately.v below the positive supply voltage to V above the negative supply. As a differential input voltage causes the output voltage to increase, however, the linear input range will be limited by the output voltage swing of amplifiers A and A. Thus, the linear common-mode input range is related to the output voltage of the complete amplifier. This behavior also depends on supply voltage see performance curves Input Common-Mode Range vs Output Voltage. Input-overload can produce an output voltage that appears normal. For example, if an input overload condition drives both input amplifiers to their positive output swing 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. LOW VOLTAGE OPERATION The can be operated on power supplies as low as ±.V. Performance of the remains excellent with power supplies ranging from ±.V to ±V. Most parameters vary only slightly throughout this supply voltage range see typical performance curves. Operation at very low supply voltage requires careful attention to assure that the input voltages remain within their linear range. Voltage swing requirements of internal nodes limit the input commonmode range with low power supply voltage. Typical performance curves, Input Common-Mode Range vs Output Voltage show the range of linear operation for a various supply voltages and gains. 9

10 SINGLE SUPPLY OPERATION The can be used on single power supplies of.7v to V. Figure shows a basic single supply circuit. The output terminal is connected to ground. Zero differential input voltage will demand an output voltage of V (ground). Actual output voltage swing is limited to approximately mv above ground, when the load is referred to ground as shown. The typical performance curve Output Voltage vs Output Current shows how the output voltage swing varies with output current. With single supply operation, and must both be.9v above ground for linear operation. You cannot, for instance, connect the inverting input to ground and measure a voltage connected to the non-inverting input. To illustrate the issues affecting low voltage operation, consider the circuit in Figure. It shows the, operating from a single V supply. A resistor in series with the low side of the bridge assures that the bridge output voltage is within the common-mode range of the amplifier s inputs. er to the typical performance curve Input Common-Mode Range vs Output Voltage for V single supply operation. 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 of approximately. to ma. The typical performance curve Input Bias Current vs Input Overload Voltage shows this input current limit behavior. The inputs are protected even if the power supplies are disconnected or turned off. INSIDE THE Figure shows a simplified representation of the. The more detailed diagram shown here provides additional insight into its operation. Each input is protected by two FET transistors that provide a low series resistance under normal signal conditions, preserving excellent noise performance. When excessive voltage is applied, these transistors limit input current to approximately. to ma. The differential input voltage is buffered by Q and Q and impressed across, causing a signal current to flow through, R and R. The output difference amp, A, removes the common-mode component of the input signal and refers the output signal to the terminal. Equations in the figure describe the output voltages of A and A. The V BE and IR drop across R and R produce output voltages on A and A that are approximately V lower than the input voltages. A Out = V CM V BE (µa kω) / A Out = V CM V BE (µa kω) / Output Swing Range A, A ; (V).V to (V).V Amplifier Linear Input Range: (V).V to (V).9V Input Bias Current Compensation µa V B µa A A C C kω = G ( ) Output Swing Range: (V).V to (V).V kω kω A Q R kω R kω Q kω V D / (External) V CM V D / FIGURE. Simplified Circuit Diagram.

11 V V V V.V REF V R R Ω V V Pt Ω R () K Cu Cu NOTE: () R required to create proper common-mode voltage, only for low voltage operation see text. FIGURE. Single-Supply Bridge Amplifier. R C MΩ.µF R Ω = RTD at C SEEBECK ISA COEFFICIENT TYPE MATERIAL (µv/ C) R, R E Chromel..kΩ Constantan J Iron. 7.kΩ Constantan K Chromel kΩ Alumel T Copper. kω Constantan FIGURE 7. Thermocouple Amplifier With Cold Junction Compensation. OPA f db = πr C =.9Hz R I B I O = R G FIGURE. AC-Coupled Instrumentation Amplifier. A I B Error A Load I O OPA77 OPA OPA ±.na ±pa ±7fA FIGURE. Differential Voltage to Current Converter..kΩ RA LA /.kω G = RL 9kΩ 9kΩ / OPA kω / OPA FIGURE 9. ECG Amplifier With Right-Leg Drive.

Precision, Low Power INSTRUMENTATION AMPLIFIERS

INA9 INA9 INA9 Precision, Low Power INSTRUMENTATION AMPLIFIERS 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