UC2845AQ: UC2845A Question about noise and temperature.

Bob Lee62837

Mastermind 7230 points

Part Number: UC2845AQ
Other Parts Discussed in Thread: UC2845A

Dear support member,

My customer made UC2845A board.
I have a question about noise and temperature.

（Situation）
After turning on the power, after several minutes it is operating as designed and operating stably.

But after that time, the ON duty of switching becomes unstable and abnormal oscillation has occurred.

（Question）
Switching has abnormally oscillated after a while.

Q1
Is this not related to temperature rise?

Q2
I think that the noise increases by changing the temperature characteristics inside the parts such as control IC and FET.
Have you ever received reports that noise increases with temperature?

Best regard.
Bob Lee.

over 5 years ago

0 John Griffin1 over 5 years ago

TI__Mastermind 34465 points

Hi Bob,
If the power supply works for several minutes with a stable output and starts to misbehave after several minutes then I would say that the problem is temperature related.
Some component within the power supply is over heating and operating beyond its capabilities.
I can say for sure this is not the UC2845A since this part has been designed into thousand of products over many many years with a proven reliability and robustness.
You need to look at the whole product design and check to see which component is being operated beyond its designed parameters.

Regards
John

0 Bob Lee62837 over 5 years ago in reply to John Griffin1

Mastermind 7230 points

Dear John Griffin1,

Thank you very much for answer.

May I add a question?

Q1
Is there a possibility that the temperature of the peripheral components rises and noise is placed on the IC side?

Q2
For example, is there a possibility that noise may appear on the ISENSE terminal due to the temperature rise of peripheral components?

Best regard.
Bob Lee.

0 John Griffin1 over 5 years ago in reply to Bob Lee62837

TI__Mastermind 34465 points

Hi Bob,
Yes there is that possibility.
However it is impossible to say exactly what is happening here.
Do you have any test waveforms which show the switching and the operating conditions or a schematic ?
Regards
John

0 Bob Lee62837 over 5 years ago in reply to John Griffin1

Mastermind 7230 points

Dear John Griffin1,

Thank you very much for reply.
I'm confirming waveform about ISENS and SW waveform.

I will feedback.

Since I want to send schematic and waveform,
Could you teach private E-mail address?

Best regard.
Bob Lee.

0 John Griffin1 over 5 years ago in reply to Bob Lee62837

TI__Mastermind 34465 points

Hi Bob Lee,
Please post your email address and I will contact you.
Regards
John

0 John Griffin1 over 5 years ago in reply to John Griffin1

TI__Mastermind 34465 points

Hi Bob Lee,
I am going to close this thread since you have not posted the required information
Please open a new thread if you have further questions.
Regards
John

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UC2845AQ: UC2845A Question about noise and temperature.