UCC256404: LLC chip failure under heavy load.

Wim Verheyen

Part Number: UCC256404
Other Parts Discussed in Thread: UCC28056, PFCLLCSREVM034

Hi,

I am designing a power supply with UCC256404 and a PFC pre-stage with UCC28056, based on a reference design PFCLLCSREVM034.

This is a 150W output power design, using an Itacoil LCC transformer, calculations are made with the UCC25640x Design Calculator Rev4.0.

Now I have trouble making this work properly, as soon as I put a load of more than ~90W, the UCC256404 stops working, no Rvcc is coming out and no switching occurs, the chip fails.

I notice that the Vcc under heay load rises to 25V or more (with no load it is 18V as expected with the transformer used).

I am a bit clueless as to what causes the chip failure, can you give me some hints ?

Of course I am willing to give more details about the design and the calculations if need be.

Kind regards,

Wim Verheyen for Joranalogue Audio Design.

7 months ago

0 Manikanta Pallantla 7 months ago

TI__Genius 13245 points

Hi Wim,

When the controlller is going into fault state, the RVCC will be zero.

please go through the debugging guidleines in the following app note to see which fault is getting triggered.

https://www.ti.com/lit/pdf/sluaaj7

Regards

Manikanta P

0 Wim Verheyen 7 months ago in reply to Manikanta Pallantla

Prodigy 10 points

Hi Manikanta,

I know about the fault states and that RVCC will go to zero for a second, this happen e.g. with overcurrent etc.

I have also read sluaaj7.

The problem I have is that the chip does not go in fault state, it just dies.

I noticed spikes on the gate signals to the MOSFETs, these do not happen on the TI evaluation board.

Regards,

Wim.

0 Wim Verheyen 7 months ago

Prodigy 10 points

I found out about the spikes on the gate signals, I need to tune the gate resistors, hopefully this solves the issue.

The spikes are indeed higher than the ratings on the HO and LO pins.

I found more info in slla385a and slua618a.

0 Manikanta Pallantla 7 months ago in reply to Wim Verheyen

TI__Genius 13245 points

Thanks for the update.

Regards

Manikanta P

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UCC256404: LLC chip failure under heavy load.