Data Sheet

AD8397

Rev. B | Page 11 of 16

APPLICATIONS INFORMATION

The AD8397 is a voltage feedback operational amplifier that

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 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. Pay careful attention to

decoupling the power supply. Use high quality capacitors with

low equivalent series resistance (ESR), such as multilayer ceramic

capacitors (MLCCs), to minimize the supply voltage ripple and

power dissipation. Locate a 0.1 μF MLCC decoupling capacitor(s)

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, pay careful attention to

printed circuit board (PCB) layout 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 capacitances. The signal routing

should be short and direct in order to minimize the parasitic

inductance and capacitance associated with these traces. Locate

termination resistors and loads as close as possible to their

respective inputs and outputs. Keep input traces 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, provide a symmetrical layout 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, use the amplifier

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