LM311P VS LM311N

Antonio Giuseppe Marra

Prodigy 40 points

Other Parts Discussed in Thread: LM311

Hi All,

what is the difference between this two component?

The same circuit work fine with the LM311N but when I use the LM311P it doesn't work.

over 8 years ago

0 Ron Michallick over 8 years ago

TI__Guru**** 152586 points

Antonio,

Two different die designs. Created by two separate companies. Both device work, if design does not violate some specification.

C1 can push pin 2 out of the valid common mode range. It can make pin 2 peak above VCC and below ground. Most concerning is below ground.

Try removing C1; does that help?

0 Antonio Giuseppe Marra over 8 years ago in reply to Ron Michallick

Prodigy 40 points

Hi Ron,
tank you for your answer, infact I removed the C1 and the circuit work fine.

I was not able to motivate the wrong behavior.

Regards
Antonio

0 Antonio Giuseppe Marra over 8 years ago in reply to Ron Michallick

Prodigy 40 points

Hi Ronald,

below you can see two trace on pin 2 of U1, the first is with LM311P, you can see a spike of -2.987V

While the second with LM311N:

The negative spike is 0.7V.

According the datasheet of the lm311N:

Why all work with LM311N?

thank you in advance.

Antonio

0 Ron Michallick over 8 years ago in reply to Antonio Giuseppe Marra

TI__Guru**** 152586 points

Antonio,

I suspect LM311P does not have a parasitic diode from input to GND pin and LM311N does have a diode.

0 Antonio Giuseppe Marra over 8 years ago in reply to Ron Michallick

Prodigy 40 points

Hi Ron,

both LM311P and LM311N have the parassitic diode, infact I used the Multimeter to meseaure if diode on pin 2 to ground was present in both models.

I tried to characterize it for both the OPAMP:

any suggestion?

Thanks in advance.

Regards

Antonio

0 Ron Michallick over 8 years ago in reply to Antonio Giuseppe Marra

TI__Guru**** 152586 points

Antonio,

It makes sense that both have diodes. However the -2.987V peak pulse that was observed means the diode is being over-stressed.
You have at least two choice , keep the capacitor out or use the LM311 that seem to ignore the transient.

If you would like to try something else. Sweep pin 2 from 0V to -0.8V and see if if the output goes high. If it does, that is called phase reversal.

Amplifiers

Amplifiers forum

LM311P VS LM311N