Datasheet AD8215 (Analog Devices) - 10

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AD8215 Data Sheet THEORY OF OPERATION
In typical applications, the AD8215 amplifies a small differential A load current flowing through the external shunt resistor input voltage generated by the load current flowing through a produces a voltage at the input terminals of the AD8215. R and shunt resistor. The AD8215 rejects high common-mode voltages R1 connect the input terminals to A1. The inverting terminal, (up to 65 V) and provides a ground-referenced, buffered output which has very high input impedance, is held to that interfaces with an analog-to-digital converter (ADC). (VCM) − (ISHUNT × RSHUNT) Figure 26 shows a simplified schematic of the AD8215. because negligible current flows through R. A1 forces the
ISHUNT
noninverting input to the same potential. Therefore, the current
RSHUNT
that flows through R1 is equal to
IIN
IIN = (ISHUNT × RSHUNT)/R1
R1 R
This current (IIN) is converted back to a voltage via ROUT. The output buffer amplifier has a gain of 20 V/V and offers excellent
A1 V+
accuracy as the internal gain setting resistors are precision trimmed
PROPRIETARY
to within 0.01% matching. The resulting output voltage is equal to
OFFSET CIRCUITRY
OUT = (ISHUNT × RSHUNT) × 20
OUT = (ISHUNT × RSHUNT) × 20 G = +20 ROUT AD8215
25 0 3- 20
GND
07 Figure 26. Simplified Schematic Rev. B | Page 10 of 13 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 APPLICATION NOTES OUTPUT LINEARITY APPLICATIONS INFORMATION HIGH-SIDE CURRENT SENSING WITH A LOW-SIDE SWITCH HIGH-SIDE CURRENT SENSING LOW-SIDE CURRENT SENSING OUTLINE DIMENSIONS ORDERING GUIDE AUTOMOTIVE PRODUCTS