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 V_S 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