AD8213YRMZ-RL(Rev0) View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
AD8213YRMZ-RL Datasheet PDF : 16 Pages
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AD8213
THEORY OF OPERATION
In typical applications, the AD8213 amplifies a small differential
input voltage generated by the load current flowing through a
shunt resistor. The AD8213 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 25 shows a simplified schematic of the AD8213.
The following explanation refers exclusively to Channel 1 of the
AD8213, however, the same explanation applies to Channel 2.
A load current flowing through the external shunt resistor
produces a voltage at the input terminals of the AD8213. The
input terminals are connected to Amplifier A1 by Resistor R1(1)
and Resistor R1(2). The inverting terminal, which has very high
input impedance is held to (VCM) – (ISHUNT × RSHUNT), since
negligible current flows through Resistor R1(2). Amplifier A1
forces the noninverting input to the same potential. Therefore,
the current that flows through Resistor R1(1), is equal to
IIN1 = (ISHUNT1 × RSHUNT1)/R1(1)
This current (IIN1) is converted back to a voltage via ROUT1. 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
VOUT1 = (ISHUNT1 × RSHUNT1) × 20
Prior to the buffer amplifier, a precision-trimmed 20 kΩ resistor
is available to perform low-pass filtering of the input signal
prior to the amplification stage. This means that the noise of the
input signal is not amplified, but rejected, resulting in a more
precise output signal that will directly interface with a converter.
A capacitor from the CF1 pin to GND, will result in a low-pass
filter with a corner frequency of
f −3dB
=
1
2π(20000 )C FILTER
R2 (1)
ISHUNT2
ISHUNT1
RSHUNT2
RSHUNT1
IIN2 IIN1
R2 (2)
R1 (1)
R1 (2)
A2
OUT2 = (ISHUNT2 × RSHUNT2) × 20
PROPRIETARY
OFFSET
CIRCUITRY
Q2
20kΩ
G = +20
ROUT2
A1
PROPRIETARY
OFFSET
CIRCUITRY
Q1
20kΩ
ROUT1
G = +20
V+
OUT1 = (ISHUNT1 × RSHUNT1) × 20
AD8213
CF2
GND
CF1
Figure 25. Simplified Schematic
Rev. 0 | Page 10 of 16
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