AD8236ARMZ-R71 datasheet(15/20 Pages) AD

15 / 20 page

AD8236

Rev. 0 | Page 15 of 20

INCORRECT

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.

CORRECT

AD8236

REF

AD8236

OP AMP

–

REF

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.

AD8236

+VS

+IN

–IN

LOAD

REF

0.1µF

10µF

0.1µF

10µF

–VS

VOUT

Figure 37. Supply Decoupling, REF, and Output Referred to Ground

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