UCC28780: Start up problem

user4578860

Part Number: UCC28780

Hi, I am trying to use UCC28780 in my design, and get stuck with start up problem. Here is the VDD and REF wave, RUN and PWML PIN without any signal. Could someone tell me why? Thanks a lot.

Thank You,

Best Regards.

over 7 years ago

0 Hong Huang over 7 years ago

TI__Guru 73455 points

Can you provide your schematics for our review? Can you probe RUN pin to see how its trace looks like?

0 user4578860 over 7 years ago in reply to Hong Huang

Prodigy 40 points

Thanks for your reply,Hong. Attach the schemic and the RUN pin's probe trace.

SCH-4512.pdf

0 Hong Huang over 7 years ago in reply to user4578860

TI__Guru 73455 points

Can you set the oscilloscope trigger to RUN to check if RUN step up at all?

0 user4578860 over 7 years ago in reply to Hong Huang

Prodigy 40 points

Sorry for the late reply.

Yes, I had already done that before, and didn't see anything. I am goning to recheck all the circut and device parameters to see whether something goes wrong. Pls tell me If you have any suggestions.Thanks again!

0 Hong Huang over 7 years ago in reply to user4578860

TI__Guru 73455 points

Can you confirm Q2 in your design correct? Is it a P-channel or a N-Channel?

0 user4578860 over 7 years ago in reply to Hong Huang

Prodigy 40 points

It's a N-Channel MOS,and the model is BSS126H6327XTSA2. Sorry I used a wrong symbol misguided you.

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UCC28780: Start up problem