AD8392ACP-R2 datasheet(11/16 Pages) AD

11 / 16 page

AD8392

Rev. 0 | Page 11 of 16

THEORY OF OPERATION

The AD8392 is a current feedback amplifier with high (400 mA)

output current capability. With a current feedback amplifier, the

current into the inverting input is the feedback signal, and the

open-loop behavior is that of a transimpedance, dVO/dIIN or TZ.

The open-loop transimpedance is analogous to the open-loop

voltage gain of a voltage feedback amplifier. Figure 33 shows a

simplified model of a current feedback amplifier. Since RIN is

proportional to 1/gm, the equivalent voltage gain is just TZ × gm,

where gm is the transconductance of the input stage. Basic

analysis of the follower with gain circuit yields

()

where:

= 1

1 ≈

Since G × RIN << RF for low gains, a current feedback amplifier

has relatively constant bandwidth versus gain, the 3 dB point

being set when |TZ| = RF.

Of course, for a real amplifier there are additional poles that

contribute excess phase, and there is a value for RF below which

the amplifier is unstable. Tolerance for peaking and desired

flatness determines the optimum RF in each application.

VOUT

VIN

RIN

IIN

Figure 33. Simplified Block Diagram

The AD8392 is capable of delivering 400 mA of output current

while swinging to within 2 V of either power supply rail. The

AD8392 also has a power management system included on-chip.

It features four user-programmable power levels (three active

power modes as well as the provision for complete shutdown).

AD8392ACP-R2 データシート(PDF) 11 Page - Analog Devices