Datasheet

Data Sheet AD8276/AD8277
Rev. C | 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:
V5.1−+<
+
S
REF
VV
R2R1
R1
For example, when operating on a +V
S
= 2 V single supply and
V
REF
= 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 V
REF
= 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 noninverting input. Therefore,
the user needs to increase the supply voltage or decrease V
REF
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, −V
S
= −5 V, + V
S
= 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.
R4
V
REF
R3
R1
R2
R1
R1 + R2
(V
REF
)
R1
R1 + R2
(V
REF
)
07692-032
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.