TPS54325/Start-up failure

Tsukui Yusuke

Guru 21930 points

Other Parts Discussed in Thread: TPS54325

Hi,

Now our customer is testing TPS54325 on theirtest board and then they can confirmed start-up failure sometimes.

Can you check and give your comments if you can find some problem points into waveform and schematic in attached?

Best Regards,

Yusuke/ Disty in Japan

7848.TPS54325 Start‐up.pdf

over 12 years ago

0 JohnTucker over 12 years ago

TI__Guru**** 191445 points

I'll look into this on Monday.

0 JohnTucker over 12 years ago in reply to JohnTucker

TI__Guru**** 191445 points

The VREG5 voltage is falling below the UVLO threshold. That is turning off the device. Is there anything connected to VREG5 externally? Is there only one device that is doing this? If so I suggest you submit it for failure analysis.

0 Tsukui Yusuke over 12 years ago in reply to JohnTucker

Guru 21930 points

Hi.

Thank you for giving a comment.

UVLO showed that Vout was not outputted.

There is nothing that is connected to vreg5.

Why is Vreg5 about 3V that Vcc is supplied 15V?

Would you teach, if some may be expected?

Best Regards,

Yusuke.

0 JohnTucker over 12 years ago in reply to Tsukui Yusuke

TI__Guru**** 191445 points

VREG5 can be disabled if EN goes low or if there is a fault condition. Can you check the SS, EN and Iout waveforms? Is this only a single device that is not working? Does it fail to start up correctly every time or does it start properly sometimes? It is possible the device may be damaged.

0 George Ioakimedes over 12 years ago

Genius 4950 points

I don't know if you solved your problem but we were having some similar start up problems with this part. We ended up changing the SS capacitor to 33nF. The value wasn't critical but it had to be lower than 0.1uF and 33nF was used on the board already.

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TPS54325/Start-up failure