AD8236 데이터 시트보기 (PDF) - Analog Devices
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AD8236 Datasheet PDF : 20 Pages
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LAYOUT
Careful board layout maximizes system performance. In
applications that need to take advantage of the low input
bias current of the AD8236, avoid placing metal under the
input path to minimize leakage current.
Grounding
The output voltage of the AD8236 is developed with respect to
the potential on the reference terminal, REF. To ensure the most
accurate output, the trace from the REF pin should either be
connected to the AD8236 local ground (see Figure 37) or
connected to a voltage that is referenced to the AD8236 local
ground (Figure 35).
REFERENCE TERMINAL
The reference terminal, REF, is at one end of a 210 kΩ resistor
(see Figure 34). The output of the instrumentation amplifier
is referenced to the voltage on the REF terminal; this is useful
when the output signal needs to be offset to voltages other than
common. For example, a voltage source can be tied to the REF
pin to level-shift the output so that the AD8236 can interface
with an ADC. The allowable reference voltage range is a function
of the gain, common-mode input, and supply voltages. The REF
pin should not exceed either +VS or −VS by more than 0.5 V.
For best performance, especially in cases where the output is not
measured with respect to the REF terminal, source impedance to
the REF terminal should be kept low because parasitic resistance
can adversely affect CMRR and gain accuracy. Figure 36
demonstrates how an op amp is configured to provide a low
source impedance to the REF terminal when a midscale
reference voltage is desired.
INCORRECT
AD8236
CORRECT
AD8236
REF
V
AD8236
V
REF
+
OP AMP
–
Figure 36. Driving the REF Pin
POWER SUPPLY REGULATION AND BYPASSING
The AD8236 has high power supply rejection ration (PSRR).
However, for optimal performance, a stable dc voltage should be
used to power the instrumentation amplifier. Noise on the supply
pins can adversely affect performance. As in all linear circuits,
bypass capacitors must be used to decouple the amplifier.
A 0.1 μF capacitor should be placed close to each supply pin.
A 10 μF tantalum capacitor can be used further away from the
part (see Figure 37). In most cases, it can be shared by other
precision integrated circuits.
+VS
0.1µF
+IN
AD8236
–IN
REF
10µF
VOUT
LOAD
0.1µF
10µF
–VS
Figure 37. Supply Decoupling, REF, and Output Referred to Ground
Rev. 0 | Page 15 of 20
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