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UCC28730: UCC28730 start-up failure.

Artur Dec
Prodigy 30 points
Part Number: UCC28730
Other Parts Discussed in Thread: UCC24650,

Welcome,

i'm having some problems with a 10 W power supply which was built using the UCC28730 controller and UCC24650 voltage monitor. The power supply schematics is basically the same as the example build UCC28730EVM-552 from UCC28730's user guides.

After switching the supply on, there is no voltage on the VDD capacitors. The capacitors are fine, the controller itself seems to be working as well (controller was also replaced but the problem did not persist). Additionally there is current flowing from the bulk capacitors to the HV pin of the controller (there is a voltage drop on the 100k resistor connecting bulk capacitor and HV pin), so the controller never exits start-up mode. I also found the TI PSR controllers troubleshooting guide but after checking the VDD voltage signal on a osciloscope, none of the described causes fit this case. Correct me if i'm wrong but the current flowing to the HV pin which doesn't charge VDD capacitors would suggest a short on the board, but there is certainly no short. 

Regards,

Artur

  • 0
    TI__Expert 5900 points
    Hi Artur,
    Could you measure the resistance between VDD and GND using DMM with or without the UCC28730 assembled?
    And could you share the schematic?

    Br
    Kening
  • 0 in reply to Kening Gao
    Prodigy 30 points
    Thank you Kening,
    The resistance beetween VDD and GND on the assembled board is 1.3k.
    This is the schematic in Eagle: http://imgur.com/a/1QHl6. Q1 is IPI65R660CFDXKSA1, D2 is BAV23A-7-F, D8 is MBRA340T3G. The rest of the components are the same as in the schematic.

    Regards,
    Artur
  • 0 in reply to Artur Dec
    TI__Expert 5900 points

    HI Artur,

    If the resistance between VDD and GND is 1.3k, something goes wrong.

    You may first disassemble the UCC28730, the measure the resistance.

    The point is to find which component or layout cause this low resistance.

    Br

    Kening

  • 0 in reply to Kening Gao
    Prodigy 30 points
    Thank you Kening,
    I disassembled the UCC28730 and measured VDD-GND resistance on the controller and it is still 1.3k. At this point point i can assume that the controller is broken, right? I'm not sure what might have caused the damage to the controller though. There aren't any shorts on the board. Do you have any idea what parts i could check again to be certain that the next installed controller won't break?
    I'll verify your answer from 9th march, thank you for your help again.

    Regards
    Artur
  • 0 in reply to Artur Dec
    TI__Expert 5900 points

    Hi Artur,

    The over stress on pins(VDD, VS, HV) could cause shorting of VDD-GND.

    First , you could measure the VDD-GND resistance for new ucc28730 before you assemble it on the board.

    Second, you could remove R4 and D6 then power on. You should observe than VDD goes up to 22V then goes down to 7.7V again and again.

    Third, please confirm the VDD voltage is not very high after you put R4 and D6 on the board again.

    Please let me know your progress.

    Br

    Kening