TPS23754 output only 3.3V

Chen Tao1

Intellectual 410 points

Other Parts Discussed in Thread: TPS23754

Hi,

We copied the TPS23754 EVM design.

We can see 52V input is ON.

But when in debug, we found Q1&Q5 always be damaged.

Would you suggest which part should be look into?

Attached is schematic.

1.jpg voltage before transformer

2.jpg voltage after transformer

POE_TI.pdf

over 9 years ago

0 Darwin Fernandez over 9 years ago

TI__Mastermind 41790 points

Hi Chen,

One thing about the schematic that catches my eye is the VC inductor is rather low. Can you measure the VC voltage on the IC? Is it oscillating down to the UV UVLO? Typically for active clamp forward converter, this inductor should be 1mH. The schematic shows 1uH.

Regards,
Darwin

0 Chen Tao1 over 9 years ago in reply to Darwin Fernandez

Intellectual 410 points

Hi, Darwin,

Yes. The inductor is already change to 1mH. But it still don't work.

0 Darwin Fernandez over 9 years ago in reply to Chen Tao1

TI__Mastermind 41790 points

Hi Chen,

Double checking the schematic, I don't see any issues that would cause the FETs to damage. Is this for all your boards? Or under certain conditions? It might be good to double check that the connections are correct on the actual board and that the components are the correct values and populated correctly. You can try measuring the impedances on the EVM and your board to verify this.

Regards,
Darwin

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TPS23754 output only 3.3V