Datasheet AD8422 (Analog Devices) - 23

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Data Sheet AD8422 APPLICATIONS INFORMATION PRECISION BRIDGE CONDITIONING
ADA4096-2, ensure that the desired output voltage of the AD8276 With its high CMRR, low drift, and rail-to-rail output, the is within its output range, and VL is within the input and output AD8422 is an excellent choice for conditioning a signal from a range of the ADA4096-2. The transistor must have sufficient Wheatstone bridge. With appropriate supply voltages, the gain breakdown voltage and IC. Low cost transistors, such as the BC847 and reference pin voltage can be adjusted to match the full-scale or 2N5210, are recommended. bridge output to any desired output range, such as 0 V to 5 V.
PROCESS CONTROL ANALOG INPUT
Figure 63 shows a circuit to convert a bridge signal into a 4 mA In process control systems such as programmable logic controllers to 20 mA output using the AD8276 low power, precision difference (PLC) and distributed control systems (DCS), analog variables amplifier, and the ADA4096-2 low power, rail-to-rail input and typically occur in just a few standard voltage or current ranges, output, overvoltage protected op amp. With high precision bridge including 4 mA to 20 mA and ±10 V. Variables within these input circuits, care must be taken to compensate offsets and temperature ranges must often be gained or attenuated and level shifted to errors. For example, if the voltage at the REF pin is used to match a specific ADC input range such as 0 V to 5 V. The circuit in compensate for the bridge offset, ensure that the AD8422 is within Figure 64 shows one way this can be done with a single AD8422. its operating range for the maximum expected offset. If the zero- Low power, overvoltage protection, and high precision make the adjust potentiometer is excluded, connect the positive op amp AD8422 a good match for process control applications, and high input to the center of the 24.9 kΩ, 10.7 kΩ divider, which is at input impedance, low bias current, and low current noise allow 1.5 V. If lower supply voltages are used for the AD8276 and the significant source resistance with minimum additional errors.
+5V +5V +IN +24V SENSE +24V V = 0.5V TO 2.5V +IN VOUT_FS = ±15mV RG AD8422 V +5V OUT REF AD8276 –IN REF 24.9kΩ +24V –IN RG = 301Ω 1 +24V 124Ω G = 66.8V/V IOUT = 4mA TO 20mA V 10.7kΩ L ADA4096-2 RL 1 ADA4096-2 OPTIONAL
066
ZERO ADJUST
11197- Figure 63. Bridge Circuit with 4 mA to 20 mA Output
TERMINAL BLOCK 0V TO 10V, ±10V 42.2kΩ 0V TO 5V, ±5V 34kΩ +15V 0V TO 1V, ±1V 1kΩ +IN 4mA TO 20mA, 8.45kΩ VOUT = 2.5V ±2.5V 0mA TO 20mA RG AD8422 ±20mA 49.9Ω REF 1kΩ 2.5V –IN –15V
067
RG = 13.2kΩ G = 2.5V/V
11197- Figure 64. Process Control Analog Input Rev. A | Page 23 of 24 Document Outline FEATURES APPLICATIONS CONNECTION DIAGRAM GENERAL DESCRIPTION TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS SOIC PACKAGE MSOP PACKAGE ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION ARCHITECTURE GAIN SELECTION RG Power Dissipation REFERENCE TERMINAL INPUT VOLTAGE RANGE LAYOUT Common-Mode Rejection Ratio over Frequency Power Supplies and Grounding Reference Pin INPUT BIAS CURRENT RETURN PATH INPUT VOLTAGES BEYOND THE SUPPLY RAILS Input Voltages Beyond the Maximum Ratings RADIO FREQUENCY INTERFERENCE (RFI) APPLICATIONS INFORMATION PRECISION BRIDGE CONDITIONING PROCESS CONTROL ANALOG INPUT OUTLINE DIMENSIONS ORDERING GUIDE