UCC28632: UCC28632 question about between VDD and GND operation when the output on the secondary side is shorted.

Bob Lee62837

Part Number: UCC28632

Dear support member,

My customer used UCC28632.

I have a question about between VDD and GND operation when the output on the secondary side is shorted.

（Situation)
When when the output on the secondary side is shorted,
Basically, I think that the rising voltage of VDD is repeated at VDD (start) level, but the VDD (start) level and rising to nearly 20 V are alternately repeated.

Waveform was not UVLO operation between VDD pins and GND pins.

（Question)
1. What kind of state (control) is this rise near 20 V?

2. Is this operation normal as the operation of the VDD pin when the secondary side output is shorted?

3. The maximum rating of the VDD voltage is 20V.
Is there a problem?
Is there a way to solve it?

Best regard.
Bob Lee.

over 4 years ago

0 Hong Huang over 4 years ago

TI__Mastermind 47325 points

Please provide your schematics to help further talk.

0 Bob Lee62837 over 4 years ago in reply to Hong Huang

Mastermind 7230 points

Dear Hong Huang,

Thank you very much for reply.

Since I send data you,
Could you teach private E-mail address?

Best regard.
Bob Lee.

0 Hong Huang over 4 years ago in reply to Bob Lee62837

TI__Mastermind 47325 points

You only need to provide the UCC28632 related portion and not need to provide the remaining circuit of yours. So there should not be a problem you provide the schematics through E2E here. In general, E2E support needs to be made through E2E.

0 Bob Lee62837 over 4 years ago in reply to Hong Huang

Mastermind 7230 points

Dear Hong Huang,

Thank you very much for reply.
Since schematics is customer's confidential information.
So it can not post to E2E.

Could you teach private E-mail address?

Best regard.
Bob Lee.

0 Hong Huang over 4 years ago in reply to Bob Lee62837

TI__Mastermind 47325 points

Who's the customer, and where is it located?

E2E support in nature needs to post on E2E. If you need to have support individually, please provide your further information so we can find what we can do.

0 Bob Lee62837 over 4 years ago in reply to Hong Huang

Mastermind 7230 points

Dear Hong Huang,

Customer is maker in Jap.
Waveform Information update.

(Waveform)
The output on the secondary side is shorted.

The waveform between VDD and GND is
(①VDD rise up to 15V from 0V、
②VDD down fall to 8V from 15V、
③VDD rise up to 20V from 8V、

④VDD down fall to 5V from 20V、
⑤VDD rise up to 15V from 5V、
⑥VDD down fall to 8V from 15V、
⑦VDD rise up to 20V from 8V)

④～⑦ waveform is repeat.

（Question)
1. What kind of state (control) is this rise near 20 V?

2. Is this operation normal as the operation of the VDD pin when the secondary side output is shorted?

3. The maximum rating of the VDD voltage is 20V.
Is there a problem?
Is there a way to solve it?

Best regard.
Bob Lee.

0 Hong Huang over 4 years ago in reply to Bob Lee62837

TI__Mastermind 47325 points

Did you attach the waveform files you mentioned? I cannot find them.

0 Bob Lee62837 over 4 years ago in reply to Hong Huang

Mastermind 7230 points

Dear Hong Huang,

I'm sorry.
I attached file.

Could you check it?

Best regard.
Bob Lee.

UCC28632_Question_190718.pdf

0 Hong Huang over 4 years ago in reply to Bob Lee62837

TI__Mastermind 47325 points

It looks the operation is normal.

①VDD rise up to 15V from 0V、

--- this is because VDD start-up at 14.75V, based on the datasheet, switching starts, internal JFET off

②VDD down fall to 8V from 15V、

--- JFET off, switching starts, there is a transition time for the aux to catch up, so there is a drop from 15V to 8V

③VDD rise up to 20V from 8V、

--- the aux takes over for VDD so VDD rises up above 8V, and gets higher, but since the output is short, the operation should be in constant current operation,

④VDD down fall to 5V from 20V、

--- constant current operaiton makes VDD drops below ts reset restart level 5V, then a brand new start up cycle repeats

⑤VDD rise up to 15V from 5V、

--- a brand new cycle starts and repeats

⑥VDD down fall to 8V from 15V、
⑦VDD rise up to 20V from 8V)

④～⑦ waveform is repeat.

0 Bob Lee62837 over 4 years ago in reply to Hong Huang

Mastermind 7230 points

Dear Hong Huang,

Thank you very much for your answer.

May I add a question?

（Question）
The VDD waveform exceeds the maximum rating of 20V.
Is there a way to solve it?

Best regard.
Bob Lee.

0 Hong Huang over 4 years ago in reply to Bob Lee62837

TI__Mastermind 47325 points

A simple way is to add a zener clamping between VDD and GND so clamp the voltage < 20V.

If you like, you can reduce the aux winding turns, say reduce 1 or 2 turns to see if ok.

0 Bob Lee62837 over 4 years ago in reply to Hong Huang

Mastermind 7230 points

Dear Hong Huang,

Thank you very much for your answer.

I reply my customer your answer.
I will feedback my customer situation.

Best regard.
Bob Lee.

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UCC28632: UCC28632 question about between VDD and GND operation when the output on the secondary side is shorted.