IN+

IN-

V±

V+

OUT

VS+

GND

GND

Only needed for

dual-supply

operation

OUT

IN-

IN+

Run the input traces

as far away from

the supply lines

as possible

Use low-ESR, ceramic

bypass capacitor

VS± or GND

11

LM397

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SNOS977F – MAY 2001 – REVISED MAY 2016

Product Folder Links: LM397

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Copyright © 2001–2016, Texas Instruments Incorporated

9 Power Supply Recommendations

Place 0.1-

μF bypass capacitors close to the power-supply pins to reduce errors coupling in from noisy or high

impedance power supplies. For more detailed information on bypass capacitor placement; see the Layout

Guidelines section.

10 Layout

10.1 Layout Guidelines

Comparators are very sensitive to input noise. For best results, maintain the following layout guidelines:

•

Use a printed-circuit-board (PCB) with a good, unbroken low-inductance ground plane. Proper grounding (use

of ground plane) helps maintain specified performance of the LM397.

•

To minimize supply noise, place a decoupling capacitor (0.1-

μF ceramic, surface-mount capacitor) as close

as possible to VS as shown in Figure 12.

•

On the inputs and the output, keep lead lengths as short as possible to avoid unwanted parasitic feedback

around the comparator. Keep inputs away from the output.

•

Solder the device directly to the PCB rather than using a socket.

•

For slow-moving input signals, take care to prevent parasitic feedback. A small capacitor (1000 pF or less)

placed between the inputs can help eliminate oscillations in the transition region. This capacitor causes some

degradation to propagation delay when the impedance is low. Run the top-side ground plane between the

output and inputs.

•

Run the ground pin ground trace under the device up to the bypass capacitor, shielding the inputs from the

outputs.

10.2 Layout Example

Figure 12. Comparator Board Layout