10.1 Layout Guidelines

Proper grounding and the use of a ground plane will help to ensure the specified performance of the LMV7235 and LMV72391. Minimizing trace lengths, reducing unwanted parasitic capacitance and using surface-mount components will also help. Comparators are very sensitive to input noise.

The LMV7235 and LMV72391 require a high-speed layout. Follow these layout guidelines:

1. Use printed-circuit board with a good, unbroken low-inductance ground plane.
2. Place a decoupling capacitor (0.1-µF, ceramic surface-mount capacitor) as close as possible to V_CC pin.
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 output.
4. Solder the device directly to the printed-circuit board 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 t_PD when the source impedance is low.
6. The top-side ground plane runs between the output and inputs.
7. Ground trace from the ground pin runs under the device up to the bypass capacitor, shielding the inputs from the outputs.