LM5180-Q1: Overshoot occurs during on / off operation

BJ Han

Expert 2035 points

Part Number: LM5180-Q1

Dear TI,
We found the following problem in the FLY BACK circuit configured by applying LM5180-Q1.
(Three identical circuits are configured on the board.)
- Problem: Abnormal operation occurs when power on / off.
> In case of ch3, when input 12V off, output voltage 15V rises to about 18V and then falls.

> In case of ch2, when input power is on, it rises to about 17V and then stabilizes at 15V.

I would like to request a cause analysis of this issue.

Please review and let us have your feedback soon.

Thank you.

over 5 years ago

0 Samuel Jaffe over 5 years ago

TI__Mastermind 25590 points

BJ,

I will look into possible cause for this operation.

In the meantime please post a higher resolution image of the schematic (part numbers are difficult to read) and please let me know which scope channels correspond to what signals on the board.

Thanks,

-Sam

0 Samuel Jaffe over 5 years ago in reply to Samuel Jaffe

TI__Mastermind 25590 points

BJ,

One initial question, what is the load on the output?

Thanks,

-Sam

0 BJ Han over 5 years ago in reply to Samuel Jaffe

Expert 2035 points

Dear Sam,

Waveforms were measured across the output cap.

The load condition is 50mA or less. (15V output is used for regulator input power and gate power supply.)

I am using TVS(SMA6T18CAY) instead of Zener diode at the output. Is there a problem with this part?

0 BJ Han over 5 years ago in reply to BJ Han

Expert 2035 points

Dear Sam,
This issue has been resolved.
The problem occurred under no load conditions.
We solved this by adding 10Kohm load resistance to the output.

0 Samuel Jaffe over 5 years ago in reply to BJ Han

TI__Mastermind 25590 points

BJ,

Great to hear! Thank you for following up.

-Sam

Power management

Power management forum

LM5180-Q1: Overshoot occurs during on / off operation