LMV344: used as simple comparator

pierre jacques

Part Number: LMV344

Hi,

I used a LMV344 circuit as a basic non-inverting comparator without hysteresis. Sometimes, I observe oscillations at the output of the circuit. The oscillations occur during the commutation phases and are they are maintained at steady state. The circuit is découpled through a bypass capacitor of 100nF. The bypass capacitor is near the circuit.

Can you help me understand why the oscillations occur.

Thanks for your help,

over 4 years ago

0 Ron Michallick over 4 years ago

TI__Guru*** 140026 points

Pierre,

Without hysteresis, any noise on the input (pin 6), the reference (pin 5), or the internal noise of the op map could cause noise or oscillation at the output. The op map is running open loop with the full DC gain as the input signals cross.

0 pierre jacques over 4 years ago in reply to Ron Michallick

Prodigy 40 points

Ron,

Thanks for your answer. Can I solve the problem by replacing the OP by a comparator or I must add a hysteresis even if I use a comparator instead of an OP.

0 Ron Michallick over 4 years ago in reply to pierre jacques

TI__Guru*** 140026 points

Pierre,

A comparator would likely be more oscillations unless the comparator had internal hysteresis. I could not find a quad comparator with internal hysteresis. It needs to be added externally.

If there was just a short oscillation time, then a much slower op amp might not have time to oscillate.

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LMV344: used as simple comparator