TPS65133 VNEG not starting up.

Ignacio Linares

Expert 1655 points

Other Parts Discussed in Thread: TPS65133

I have a customer who described the following issues on TPS65133:

Problem: No negative rail developed at all.... does not even seem to try to start the SMPS.

+5V rail = fine, starts up.

Supply - both per circuit attached, and we did jumper leads to a lab linear 3V3 supply direct to part.

Diagnostics:

Part number on device confirmed to data sheet (so we have the right part) Inductors changed out from ferrite to iron core/lower DCR Caps (big/lowDCR) added everywhere Earth couplings changed to look like a copper mine between Cin, Cout, Inductor rear end.

Load taken off, down stream regulators taken out, Finger waggling (yup) and a stern telling off.....

No joy - no Vneg what so ever, not a sniff.

This is happening on more than one board - three exactly the same so far.

Any ideas what to try next?

over 11 years ago

0 Ignacio Linares over 11 years ago

Expert 1655 points

They have also already swapped out the inductor for another one - wound on an iron core like they say in the Datasheet, however no effect. In the design they are using a ferrite, part number Wurth 74479887247A - Mouser 710-74479887247A, in both places, and resaonably confident that is ok.

Checked against datasheet schematic - no obvious errors.

0 Ignacio Linares over 11 years ago in reply to Ignacio Linares

Expert 1655 points

The customer just replied with the following information. Can you confirm this is a valid fix? If so, what would have caused and why is this not included in any of the documentation?

It must be an internal clamping issue we think. Without the diode it seems to destroy the part :-)

We have put a diode in the design, and we are modifying the other boards. We will buy some more parts and fix the two we blew up.

0 Stefan Herteg over 10 years ago

Prodigy 120 points

Probably is too late but may be useful for other designers: Had the same issue and adding a bulk capacitor on the input (PVIN-PGND) 220uF.fixed the issue.

Nice part, too bad is hard to find.