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AD8215

High Voltage, Current Shunt Monitor

Analog Devices 

AD8215

THEORY OF OPERATION

In typical applications, the AD8215 amplifies a small differential

input voltage generated by the load current flowing through a

shunt resistor. The AD8215 rejects high common-mode voltages

(up to 65 V) and provides a ground-referenced, buffered output

that interfaces with an analog-to-digital converter (ADC).

Figure 26 shows a simplified schematic of the AD8215.

ISHUNT

RSHUNT

IIN

R1

R

A1

V+

PROPRIETARY

OFFSET

CIRCUITRY

ROUT

G = +20

OUT =

(ISHUNT × RSHUNT) × 20

AD8215

GND

Figure 26. Simplified Schematic

Data Sheet

A load current flowing through the external shunt resistor

produces a voltage at the input terminals of the AD8215. R and

R1 connect the input terminals to A1. The inverting terminal,

which has very high input impedance, is held to

(VCM) − (ISHUNT × RSHUNT)

because negligible current flows through R. A1 forces the

noninverting input to the same potential. Therefore, the current

that flows through R1 is equal to

IIN = (ISHUNT × RSHUNT)/R1

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

accuracy as the internal gain setting resistors are precision trimmed

to within 0.01% matching. The resulting output voltage is equal to

OUT = (ISHUNT × RSHUNT) × 20

Rev. B | Page 10 of 13

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