Datasheet AD8216 (Analog Devices) - 10

link to page 10
AD8216 Data Sheet THEORY OF OPERATION
The AD8216 is a single-supply difference amplifier typically used The reference inputs, VREF1 and VREF2, are tied through resistors to accurately amplify a smal differential current shunt voltage in to the positive input of A1, which allows the output offset to be the presence of a rapidly changing common-mode voltage. adjusted anywhere in the output operating range. The gain is 1 V/V from the reference pins to the output when the reference The AD8216 consists of an amplifier (A1), a resistor network, pins are used in parallel. When they are used to divide the supply, a small voltage reference, and a bias circuit (not shown), the gain is 0.5 V/V. see Figure 23. The ratios of RA, RB, RC, and RF are trimmed to a high level of The set of input attenuators preceding A1 consist of RA, RB, and precision to allow the CMRR to exceed 80 dB. This performance is RC, which feature a combined series resistance of approximately accomplished by laser trimming the resistor ratio matching to 200 kΩ ± 20%. The purpose of these resistors is to attenuate the better than 0.01%. input voltage to match the input voltage range of A1. This balanced resistor network attenuates the common-mode signal
+IN –IN
by a ratio of 1/18. A1 amplifier inputs are held within the power
RA RA
supply range, even if Pin 1 and Pin 8 exceed the supply or fall below common (ground). A reference voltage of 250 mV biases
A1 VOUT
the attenuator above ground, which allows the amplifier to
R R F V B RB REF1
operate in the presence of negative common-mode voltages.
RREF
The input resistor network also attenuates normal (differential)
R R C RC REF
mode voltages. Therefore, Amplifier A1 features a gain of
VREF2 AD8216
54 V/V to provide a total system gain of 3V/V.
250mV
028 Total Gain (V/V) = 1/18 (V/V) × 54 (V/V) = 3 V/V
GND
07062- Figure 23. Simplified Schematic Rev. C | Page 10 of 16 Document Outline FEATURES APPLICATIONS FUNCTIONAL BLOCK DIAGRAM GENERAL DESCRIPTION TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION OUTPUT OFFSET ADJUSTMENT UNIDIRECTIONAL OPERATION GROUND REFERENCED OUTPUT V+ REFERENCED OUTPUT BIDIRECTIONAL OPERATION EXTERNAL REFERENCED OUTPUT SPLITTING THE SUPPLY SPLITTING AN EXTERNAL REFERENCE APPLICATIONS INFORMATION HIGH-SIDE CURRENT SENSE WITH A LOW-SIDE SWITCH HIGH-SIDE CURRENT SENSE WITH A HIGH-SIDE SWITCH OUTLINE DIMENSIONS ORDERING GUIDE AUTOMOTIVE PRODUCTS