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PMP9638: I'm copying the design in to Eagle, already printed and assembled into PCB, but didn't working...

Hamid Rasyid
Prodigy 25 points
Part Number: PMP9638

Hello, 

Need help. We are developing the design from TI reference design PM9638 which we copying the schematic document into Eagle as attached in picture

All components and pads are fit into board and soldered very well. But, the supply output are not working.

The test result:

- TP 1 output are just around 2 Volts instead of 12v

- TP 3 output just 0.5 Volts instead of 3.3v

- After a while the fuse F1 was broken

I already check the schematic over and over, but seems like nothing wrong. Please tell if there's something wrong in schematic.

Thanks in advance

  • 0
    TI__Intellectual 2770 points

    Hello Hamid,

    a "remote" troubleshooting is almost impossible,
    this needs to sit in front of the PCB at the lab.

    If schematics is good please check netlist, layout and assembly next.
    Assembly means - check every part and it's orientation.

    For troubleshooting by measurements start at the input and go ahead towards output
    or vice versa, start at the output on secondary side and go towards input.

    Best regards, Bernd

  • 0 in reply to Bernd Geck
    TI__Expert 4260 points

    Hi Hamid,

    Are you using the same Wurth 750314727 transformer? What's the fuse current rating are you using?

    Please check flyback switching waveform to make sure it is operated as desired.

    Regards,

    Sheng-Yang Yu

  • 0 in reply to Sheng-yang Yu1
    Prodigy 25 points

    Hello Sheng-Yang Yu,

    Yes we are using same Wurth 750314727 transformer. We ordered directly to Wurth specially for PMP9638.

    The fuse current rating are 2A 250V. Same as mentioned at BOM list PMP9638.

    Alright, I will check the waveform, but can you suggest where I point the measurement probe for check flyback switching waveform?

    Thanks.

  • 0 in reply to Hamid Rasyid
    TI__Expert 4260 points

    Hamid,

    Sorry for my late reply.

    I think you should try to check Q3 drain to ground waveform and compare it with what I have in the test report under the same input/output conditions.

    With only 2V and 0.5V outputs, feedback isn't activated. There must be some component/board issues on the input side or output rectifier.

    Did you notice which part gets hot before fuse blow up?

    Does Zener diodes on the board have correct Vz rating?

    Does all the diodes soldered in a right polarity? 

    If you have high voltage DC source, you should check with using DC source as input.

    You should also check the current sense resistor voltage to see if the it reaches over current protection level?

    Regards,

    Sheng-Yang Yu