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INA121

FET-Input, Low Power INSTRUMENTATION AMPLIFIER

INA121
FET-Input, Low Power INSTRUMENTATION AMPLIFIER
FEATURES
DESCRIPTION
APPLICATIONS
q LOW-LEVEL TRANSDUCER AMPLIFIERS Bridge, RTD, Thermocouple q PHYSIOLOGICAL AMPLIFIERS ECG, EEG, EMG, Respiratory q HIGH IMPEDANCE TRANSDUCERS q CAPACITIVE SENSORS q MULTI-CHANNEL DATA ACQUISITION q PORTABLE, BATTERY OPERATED SYSTEMS q GENERAL PURPOSE INSTRUMENTATION
V+ 7 INA121
Over-Voltage Protection
A1 40k 25k 40k
50k RG
RG 8 25k A2 40k
Over-Voltage Protection
International Airport Industrial Park · Mailing Address: PO Box 11400, Tucson, AZ 85734 · Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 · Tel: (520) 746-1111 · Twx: 910-952-1111 Internet: http://www.burr-brown.com / · FAXLine: (800) 548-6133 (US / Canada Only) · Cable: BBRCORP · Telex: 066-6491 · FAX: (520) 889-1510 · Immediate Product Info: (800) 548-6132
PDS-1412A 1
INA121
Printed in U.S.A. May, 1998
SBOS078
Gain vs Temperature(1) Nonlinearity
OUTPUT Voltage: Positive Negative Positive Negative Capacitance Load Drive Short-Circuit Current FREQUENCY RESPONSE Bandwidth, -3dB
(V+)-1.5 (V-)+1
Overload Recovery POWER SUPPLY Voltage Range Quiescent Current TEMPERATURE RANGE Specification Operating Storage Thermal Resistance, JA 8-Lead DIP SO-8 Surface Mount T Specification same as INA121P, U.
NOTE: (1) Temperature coefficient of the "Internal Resistor" in the gain equation. Does not include TCR of gain-setting resistor, RG.
INA121
PIN CONFIGURATION
Top View 8-Pin DIP and SO-8
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.
Top View RG V-IN V
RG V+ VO Ref
ABSOLUTE MAXIMUM RATINGS(1)
PACKAGE / ORDERING INFORMATION
PACKAGE DRAWING NUMBER(1) 006 006 182 " 182 " SPECIFIED TEMPERATURE RANGE -40°C to +85°C -40°C to +85°C -40°C to +85°C " -40°C to +85°C " PACKAGE MARKING INA121P INA121PA INA121U " INA121UA " ORDERING NUMBER(2) INA121P INA121PA INA121U INA121U / 2K5 INA121UA INA121UA / 2K5 TRANSPORT MEDIA Rails Rails Rails Tape and Reel Rails Tape and Reel
PRODUCT Single INA121P INA121PA INA121U " INA121UA "
PACKAGE 8-Pin DIP 8-Pin DIP SO-8 Surface-Mount " SO-8 Surface-Mount "
NOTES: (1) For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book. (2) 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 "INA121U / 2K5" will get a single 2500-piece Tape and Reel. For detailed Tape and Reel mechanical information, refer to Appendix B of Burr-Brown IC Data Book.
INA121
TYPICAL PERFORMANCE CURVES
GAIN vs FREQUENCY 60
COMMON-MODE REJECTION vs FREQUENCY 120
Common-Mode Rejection (dB)
Gain (dB)
Frequency (Hz)
POSITIVE POWER SUPPLY REJECTION vs FREQUENCY 120 120
Power Supply Rejection (dB)
Common-Mode Voltage (V)
Ref -15V
Output Voltage (V)
INA121
TYPICAL PERFORMANCE CURVES
(CONT)
INPUT BIAS CURRENT vs TEMPERATURE 10k 1k
Bias Current (pA)
Input Bias Current (A)
1m 100µ 10µ 10p 1p -10µ -100µ
INPUT BIAS CURRENT vs COMMON-MODE INPUT VOLTAGE
100 10 1 0.1 0.01 -75 IB IOS
-1m -20 -15 -10 -5 0 5 10 15 20 Common-Mode Voltage (V)
Temperature (°C)
INPUT OVER-VOLTAGE V / I CHARACTERISTICS 1 0.8 0.6
Input Current (mA)
SETTLING TIME vs GAIN 1000
Settling Time (µs)
Flat region represents normal linear operation.
10 Gain (V / V)
Input Voltage (V)
SHORT-CIRCUIT CURRENT vs TEMPERATURE
Quiescent Current (µA)
475 IQ 450
Short-Circuit Current (µA)
Slew Rate (V / µs)
425 SR 400
375 -75 -50 -25 0 25 50 75 100 Temperature (°C)
Temperature (°C)
INA121
TYPICAL PERFORMANCE CURVES
(CONT)
OUTPUT VOLTAGE SWING vs OUTPUT CURRENT V+ (V+) -0.3 +85°C +25°C -40°C, -55°C +125°C
MAXIMUM OUTPUT VOLTAGE vs FREQUENCY 30
Peak-to-Peak Output Voltage (Vp-p)
Output Voltage Swing (V)
+25°C -40°C, -55°C
10k Frequency (Hz)
Output Current (mA)
INPUT OFFSET VOLTAGE WARM-UP 10 8
Offset Voltage Change (µV)
INPUT OFFSET VOLTAGE DRIFT PRODUCTION DISTRIBUTION Typical production distribution of packaged units.
6 4 2 0 -2 -4 -6 -8 -10 0 100 200 300 400 Time (µs) 500
0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 Offset Voltage Drift (µV / °C)
INPUT-REFERRED NOISE VOLTAGE vs FREQUENCY 1000
VOLTAGE NOISE 0.1 TO 10Hz INPUT-REFERRED, G 100
Voltage Noise (nV / Hz)
1 1 10 100 Frequency (Hz) 1k 10k
0.5µV
INA121
TYPICAL PERFORMANCE CURVES
(CONT)
50mV / div
10µs / div
100µs / div
INA121
APPLICATION INFORMATION
Commonly used gains and resistor values are shown in Figure 1.
V+ 0.1µF
7 - VIN 2 Over-Voltage Protection INA121 A1 40k 25k RG 8 25k A2 40k 40k 5 Ref A3 6
DESIRED GAIN 1 2 5 10 20 50 100 200 500 1000 2000 5000 10000
RG () NC 50.00k 12.50k 5.556k 2.632k 1.02k 505.1 251.3 100.2 50.05 25.01 10.00 5.001
50k RG
Load VO
Over-Voltage Protection
0.1µF
NC: No Connection.
Also drawn in simplified form: - VIN RG + VIN INA121 Ref VO
FIGURE 1. Basic Connections.
INA121
Input circuitry must provide a path for this input bias current if the INA121 is to operate properly. Figure 3 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 INA121 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 3). With higher source impedance, using two resistors provides a balanced input with possible advantages of lower input offset voltage due to bias current and better high-frequency common-mode rejection.
Crystal or Ceramic Transducer
INA121
Thermocouple
INA121
- VIN RG + VIN INA121 Ref
V+ 100µA 1 / 2 REF200
Center-tap provides bias current return.
INA121
Bridge
Bridge resistance provides bias current return.
NOTE: (1) For wider trim range required in high gains, scale resistor values larger V-
100µA 1 / 2 REF200
FIGURE 3. Providing an Input Common-Mode Current Path. INPUT COMMON-MODE RANGE The linear input voltage range of the input circuitry of the INA121 is from approximately 1.2V below the positive supply voltage to 2.1V above the negative supply. A differential input voltage causes the output voltage to increase. The linear input range, however, will be limited by the output voltage swing of amplifiers A1 and A2. So the linear common-mode input range is related to the output voltage of the complete amplifier. This behavior also depends on supply voltage-see typical performance curve "Input Common-Mode Range vs Output Voltage".
FIGURE 2. Optional Trimming of Output Offset Voltage. INPUT BIAS CURRENT RETURN PATH The input impedance of the INA121 is extremely high- approximately 1012. However, a path must be provided for the input bias current of both inputs. This input bias current is typically 4pA. High input impedance means that this input bias current changes very little with varying input voltage.
INA121
FIGURE 4. Voltage Swing of A1 and A2.
C1 VIN C3 INA121 Ref
R2 VIN
INA121 Ref
FET input allows use of large resistors and small capacitors.
FIGURE 5. Input Low-Pass Filter.
FIGURE 6. Bridge Transducer Amplifier. 10
INA121
INA121 Ref
1 2R1C1
INA121 VIN
ISO124
Isolated Common
FIGURE 7. High-Pass Input Filter.
FIGURE 8. Galvanically Isolated Instrumentation Amplifier.
VIN OPA277
- VIN + RG INA121 Ref C1 0.1µF
C1 50nF
R1 10k INA121 RG R2 VIN G · R2
OPA277
FIGURE 9. AC-Coupled Instrumentation Amplifier.
FIGURE 10. Voltage Controlled Current Source.
VAC R1 R2
C1 Transducer
C2 Null
INA121 Ref
FIGURE 11. Capacitive Bridge Transducer Circuit.
INA121
+5V VREF Channel 1 VIN + - MPC800 MUX Channel 8 VIN + - +In RG INA121 -In Ref ADS7816 12 Bits Out Serial
FIGURE 12. Multiplexed-Input Data Acquisition System.
22.1k 22.1k
INA121 Ref
100 NOTE: Driving the shield minimizes CMR degradation due to unequally distributed capacitance on the input line. The shield is driven at approximately 1V below the common-mode input voltage. OPA130
FIGURE 13. Shield Driver Circuit.
FIGURE 14. ECG Amplifier With Right-Leg Drive.
INA121