AD8397

Rev. 0 | Page 11 of 16

GENERAL DESCRIPTION

The AD8397 is a voltage feedback operational amplifier which

features an H-bridge input stage and common-emitter, rail-to-

rail output stage. The AD8397 can operate from a wide supply

range, ±1.5 V to ±12 V. When driving light loads, the rail-to-rail

output is capable of swinging to within 0.2 V of either rail. The

output can also deliver high linear output current when driving

heavy loads, up to 310 mA into 32 Ω while maintaining −80 dBc

SFDR. The AD8397 is fabricated on Analog Devices’ proprietary

eXtra Fast Complementary Bipolar High Voltage process

(XFCB-HV).

POWER SUPPLY AND DECOUPLING

The AD8397 can be powered with a good quality, well-

regulated, low noise supply from ±1.5 V to ±12 V. Careful

attention should be paid to decoupling the power supply. High

quality capacitors with low equivalent series resistance (ESR),

such as multilayer ceramic capacitors (MLCCs), should be used

to minimize the supply voltage ripple and power dissipation. A

0.1 µF MLCC decoupling capacitor(s) should be located no

more than 1/8 inch away from the power supply pin(s). A large

tantalum 10 µF to 47 µF capacitor is recommended to provide

good decoupling for lower frequency signals and to supply

current for fast, large signal changes at the AD8397 outputs.

LAYOUT CONSIDERATIONS

As with all high speed applications, careful attention should be

paid to printed circuit board (PCB) layout in order to prevent

associated board parasitics from becoming problematic. The

PCB should have a low impedance return path (or ground) to

the supply. Removing the ground plane from all layers in the

immediate area of the amplifier helps to reduce stray capacitan-

ces. The signal routing should be short and direct in order to

minimize the parasitic inductance and capacitance associated

with these traces. Termination resistors and loads should be

located as close as possible to their respective inputs and

outputs. Input traces should be kept as far apart as possible

from the output traces to minimize coupling (crosstalk) though

the board.

When the AD8397 is configured as a differential driver, as in

some line driving applications, a symmetrical layout should be

provided to the extent possible in order to maximize balanced

performance. When running differential signals over a long

distance, the traces on the PCB should be close together or

any differential wiring should be twisted together to minimize

the area of the inductive loop that is formed. This reduces the

radiated energy and makes the circuit less susceptible to RF

interference. Adherence to stripline design techniques for

long signal traces (greater than approximately 1 inch) is

recommended.

UNITY-GAIN OUTPUT SWING

When operating the AD8397 in a unity-gain configuration,

the output does not swing to the rails and is constrained by

the H-bridge input. This can be seen by comparing the output

overdrive recovery in Figure 7 and the input overdrive recovery

in Figure 22. To avoid overdriving the input and to realize the

full swing afforded by the rail-to-rail output stage, the amplifier

should be used in a gain of two or greater.

INPUT

OUTPUT

7

–1

0

1

0

80

160

240

320

400

TIME (ns)

480

560

640

720

800

2

3

4

5

6

Figure 22. Unity-Gain Input Overdrive Recovery