LM324B: Question about how to use LM324B.

Hi Kazuya-san,

Kazuya Nakai59 said:

Q1. When LM324B is in power down (no power applied),
    is it allow to apply any voltage to OUT pin?

Per LM324B, here is the absolute max. ratings.

Although it did not say explicitly in this particular datasheet, less than 300mV at the unpowered op amp's output (e.g. < ±0.3V) may be considered safe. An unpowered op amp's output should have high output impedance behaviors, however, internal to each pin, ESD protection diodes are present. If forward biased voltage to the internal diodes are exceeded, the diode will start to conduct and potentially it will cause damages to the op amp. 

ESD events are such example, but the duration is very short and internal ESD protection diodes are designed to handle the short duration energy spikes without damaging the op amps. 

Kazuya Nakai59 said:

Q2. If Q1 answer is yes, how much voltage can be applied to OUT pin?

Less than ±300mV may be considered safe and current has to be limited within a few mA. Are we talking about continuous voltage presence at the output of an unpowered op amp? There is another factor, which is time. Over a long duration, such stressed condition may degrade the op amp slightly, but I do not want to speculate. 

If you have other questions, please let me know. 

Best,

Raymond

Hi Raymond,

Thank you very much for your reply.

I understood that it is not allowed to applied 300mV or more voltage to OUT pin.

Could I ask you the following for just make sure?

 Q. Is it allow to apply any voltage to IN+/IN- pin when LM324B is in power down (no power applied) if the voltage is less than 40V?

Thank you again and best regards,
Kazuya.