Datasheet

AD8005
–11–
REV. A
Increasing Feedback Resistors
Unlike conventional voltage feedback op amps, the choice of feed-
back resistor has a direct impact on the closed-loop bandwidth
and stability of a current feedback op amp circuit. Reducing the
resistance below the recommended value makes the amplifier
more unstable. Increasing the size of the feedback resistor
reduces the closed-loop bandwidth.
V
OUT
+5V
562V
4.99kV
2V (rms)
–5V
AD8005
V
IN
0.2V (rms)
QUIESCENT CURRENT
475mA (MAX)
360mA (rms)
Figure 33. Saving Power by Increasing Feedback Resistor
Network
In power-critical applications where some bandwidth can be
sacrificed, increasing the size of the feedback resistor will yield
significant power savings. A good example of this is the gain of
+10 case. Operating from a bipolar supply (±5 V), the quiescent
current is 475 µA (excluding the feedback network). The recom-
mended feedback and gain resistors are 499 Ω and 56.2 Ω
respectively. In order to drive an rms output voltage of 2 V, the
output must deliver a current of 3.6 mA to the feedback net-
work. Increasing the size of the resistor network by a factor of
10 as shown in Figure 33 will reduce this current to 360 µA.
The closed loop bandwidth will however decrease to 20 MHz.