TPS23758: Inductance question

AJ Cheng

Genius 3615 points

Part Number: TPS23758

Dear Sir.

We are currently experiencing a problem. The capacitors in front of or behind L3 will Broken one of them.

It will happen when the board is powered on for the first time. What is the reason?

In addition. What is the role of L3 here?

over 5 years ago

0 Michael Pahl over 5 years ago

TI__Mastermind 21320 points

Hello A.J.,

L3 provides an additional layer of filtering of transient switching current on the input.

How are you powering the board when it is damaged? Is this a PSE or PoE injector? I am curious if the PD is negotiating power and power is applied, or if power is being injected no matter what.

Additionally can you provide a full schematic?

Regards,

Michael Pahl

0 chunnan lin over 5 years ago in reply to Michael Pahl

Prodigy 50 points

Hi Michael:

We are using POE injector.

The schematic as attachment.

Please help to review it.

Why the capacitors in front of or behind L3 will Broken one of them.

Thanks

POE_BOARD.pdf

0 Michael Pahl over 5 years ago in reply to chunnan lin

TI__Mastermind 21320 points

Hello,

Thank you for the schematic. I reviewed it and it seems okay at first glance. I have seen before that the schematic is correct but the board is not populated correctly. These capacitors are rated for 100V, so it is surprising they are breaking versus other parts. I would double check these components on the board.

Regards,

Michael Pahl

0 chunnan lin over 5 years ago in reply to Michael Pahl

Prodigy 50 points

Hi Michael:

Usually it will be broken on the first power-up.

When i change the damage capacitor it is no problem.

0 Michael Pahl over 5 years ago in reply to chunnan lin

TI__Mastermind 21320 points

Hello,

Since there is no problem when the capacitor is changed, I suspect the capacitors are the incorrect voltage rating initially. I would test an initial board and test the capacitors used.

Regards,

Michael Pahl

0 chunnan lin over 5 years ago in reply to Michael Pahl

Prodigy 50 points

Hi Michael:

Change of capacitors in our tests still encounter.

0 Michael Pahl over 5 years ago in reply to chunnan lin

TI__Mastermind 21320 points

Hello,

So my understanding is when you change the components to the correct values the problem still exists? Different from the previous message on 12/4/2019?

If this is the case, I would check the clamping diode to make sure this is the correct part. Next, please provide a scope shot of VDD-RTN during the initial power up. We can check to see the transient on the board.

Lastly, I would check the connections on the board for these parts. Ensure each part has the proper connections as listed in the schematic. Ensure the grounds are isolated from one another.

Regards,

Michael Pahl

Power management

Power management forum

TPS23758: Inductance question