LM339: LM339 noise at the reference pin

Yang Wu

Part Number: LM339

Hi Team,

My customer has a cooker working normally for 5 years. Now they changed the manufacturing factory, problem occurred.

there has a noise at the ref pin of LM339, resulting in fause trigger of the IGBT when turning up the input power of the cooker.

Green is the waveform at the ref pin, yellow is the IGBT drive signal.

So, do you have some ideas about this issue? (Note that this issue occurred after changing the manufacturing factory, it worked well before this)

Thanks a lot,

Yang

over 5 years ago

0 kai klaas69 over 5 years ago

Guru 140200 points

Hi Yang,

I would remove C69.

What role plays C62?

Kai

0 Paul Grohe over 5 years ago

TI__Guru 53846 points

Hi Yang,

Was the ringing present before the change?

What else has "changed"? Is the new factory sourcing the components? Have they verified that all the values being stuffed are correct?

Looks like C69 is a 100pF "EMI" filter cap. Please remove it as this interferes with the hysteresis AND is possibly coupling in the noise from the input into the reference.

If the scope photo is true, there is more than -10V on the ringing at the output! If this is true, this can cause the LM339 to false-trigger, as the LM339 family does not like any of it's pins taken below the GND pin.

Hopefully this is a scope probe grounding problem. Ground the scope *AT* pin 4 with a short ground lead.

0 Yang Wu over 5 years ago in reply to kai klaas69

TI__Expert 3090 points

Hi Kai,

Thanks for your suggestion. I am checking the sch to know C62's function.

Yang

0 Yang Wu over 5 years ago in reply to Paul Grohe

TI__Expert 3090 points

Hi Paul,

I will go to the filed to check with the customer and see what really happens.

Thanks a lot.

Yang

0 kai klaas69 over 5 years ago in reply to Yang Wu

Guru 140200 points

Hi Yang,

one add: Is the "A+5V" supply voltage properly regulated? Could the ringing enter the LM339 from this place?

Kai

0 Chuck Sins over 5 years ago in reply to kai klaas69

TI__Mastermind 24530 points

Yang
We have not heard back from you on this post, so I will close this thread. If you need further support, just hit reply and the thread will be re-opened.
thanks
Chuck

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LM339: LM339 noise at the reference pin