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LMV331TP / LMV393TP

General Purpose, 1.8V, RRI, Open-Drain Output Comparators

REV1.4

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Power Supply Layout and Bypass

The LMV331-393’s power supply pin should have a local bypass capacitor (i.e., 0.01μF to 0.1μF) within 2mm for

good high frequency performance. It can also use a bulk capacitor (i.e., 1μF or larger) within 100mm to provide

large, slow currents. This bulk capacitor can be shared with other analog parts.

Good ground layout improves performance by decreasing the amount of stray capacitance and noise at the

comparator’s inputs and outputs. To decrease stray capacitance, minimize PCB lengths and resistor leads, and

place external components as close to the comparator’ pins as possible.

Proper Board Layout

The LMV331-393 are a series of fast-switching, high-speed comparator and requires high-speed layout

considerations. For best results, the following layout guidelines should be followed:

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

2. Place a decoupling capacitor (0.1μF ceramic, surface-mount capacitor) as close as possible to supply.

3. 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.

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

5. 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. The topside ground plane should be placed

between the output and inputs.

6. The ground pin ground trace should run under the device up to the bypass capacitor, thus shielding the inputs

from the outputs.