AD8218(RevA) 데이터 시트보기 (PDF) - Analog Devices
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AD8218 Datasheet PDF : 16 Pages
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AD8218
THEORY OF OPERATION
AMPLIFIER CORE
In typical applications, the AD8218 amplifies a small differential
input voltage generated by the load current flowing through
a shunt resistor. The AD8218 rejects high common-mode vol-
tages (up to 80 V) and provides a ground-referenced, buffered
output. Figure 27 shows a simplified schematic of the AD8218.
ILOAD
ICHARGE
AD8218
5V CF
VS GND
R4
V2
LOAD
V1
4V
TO
80V
–IN
SHUNT +IN
ENB
R1
R2
LDO R3
OUT
REF
VREF
GND
Figure 27. Simplified Schematic
The AD8218 is configured as a difference amplifier. The
transfer function is
OUT = ((R4/R1) × (V1 − V2)) + VREF
Resistors R4 and R1 are matched to within 0.01% and have
values of 1.5 MΩ and 75 kΩ, respectively, meaning an input-
to-output total gain of 20 V/V for the AD8218. The difference
between V1 and V2 is the voltage across the shunt resistor, or
VIN. Therefore, the input-to-output transfer function of the
AD8218 is
OUT (V) = (20 × VIN) + VREF
The AD8218 accurately amplifies the input differential signal,
rejecting high voltage common modes ranging from 4 V to 80 V.
The main amplifier uses a novel zero-drift architecture, providing
the end user with breakthrough temperature stability. The
offset drift is typically less than ±100 nV/°C. This performance
leads to optimal accuracy and dynamic range.
OUTPUT CLAMPING
After the input common-mode voltage in the application is
above 5.2 V, the internal LDO output of the AD8218 also
reaches its maximum value of 5.2 V, which is the maximum
output range of the AD8218. Because in typical applications
the output interfaces with a converter, clamping the AD8218
output voltage to 5.2 V ensures that the ADC input is not
damaged due to excessive overvoltage.
Rev. A | Page 10 of 16
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