AD8276BRMZ-R7 datasheet(15/20 Pages) AD

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AD8276/AD8277

Rev. A | Page 15 of 20

POWER SUPPLIES

The AD8276/AD8277 operate extremely well over a very wide

range of supply voltages. They can operate on a single supply as

low as 2 V and as high as 36 V, under appropriate setup conditions.

For best performance, the user must exercise care that the setup

conditions ensure that the internal op amp is biased correctly.

The internal input terminals of the op amp must have sufficient

voltage headroom to operate properly. Proper operation of the

part requires at least 1.5 V between the positive supply rail and

the op amp input terminals. This relationship is expressed in

the following equation:

−

REF

For example, when operating on a +VS = 2 V single supply and

VREF = 0 V, it can be seen from Figure 40 that the input terminals

of the op amp are biased at 0 V, allowing more than the required

1.5 V headroom. However, if VREF = 1 V under the same conditions,

the input terminals of the op amp are biased at 0.5 V, barely

allowing the required 1.5 V headroom. This setup does not allow

any practical voltage swing on the non inverting input. Therefore,

the user needs to increase the supply voltage or decrease VREF to

restore proper operation.

The AD8276/AD8277 are typically specified at single- and dual-

supplies, but they can be used with unbalanced supplies, as well;

for example, −VS = −5 V, +VS = 20 V. The difference between the

two supplies must be kept below 36 V. The positive supply rail

must be at least 2 V above the negative supply and reference

voltage.

VREF

R1 + R2

(VREF)

R1 + R2

(VREF)

Figure 40. Ensure Sufficient Voltage Headroom on the Internal Op Amp

Inputs

Use a stable dc voltage to power the AD8276/AD8277. Noise on

the supply pins can adversely affect performance. Place a bypass

capacitor of 0.1 μF between each supply pin and ground, as

close as possible to each supply pin. Use a tantalum capacitor

of 10 μF between each supply and ground. It can be farther

away from the supply pins and, typically, it can be shared by

other precision integrated circuits.

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