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TPS65185 Output Voltage Issue

Pankaj Rana
Prodigy 30 points
Other Parts Discussed in Thread: TPS65185

Hi,

I am working with TPS65185, used in an addon card to support Eink EPD, with Freescale's SoloLite EVK. All the voltages are coming fine as expected, except for the VDDH(22V) and VPOS (15V).

Currently 

 VDDH(22V) = 10V

 VPOS (15V) = 16V

Let me know your suggestions/comments to resolve this issue.

Thanks.

Regards,

Pankaj Rana

  • 0
    TI__Prodigy 730 points

    Hi Pankaj, 

    What is the voltage at the VDDH_FB pin (pin 33)? Can you get a scope waveform of VDDH startup? I suspect the part is damaged because VDDH should not go below the input voltage which is 16V. 

    As for VPOS, can you add a small resistive load to the unit, say 5k or 10k? Does this cause VPOS to regulate properly? 

    Thanks, 

    Matt

  • 0 in reply to Matt Roberts
    Prodigy 30 points
    Hi Matt,

    Thanks for your reply.

    Good news is that, now we are able to get +22V VDDH. We found oscillations in the output circuit. After adding 0.1uF cap. we could get a stable Vddh measuring +22V.

    But still the problem persists for VPOS, we are getting +16V Vpos. Not yet tried adding resistive load, will revert back on it.

    P.S.: The VPOS design is similar to the Board developed by TI to evaluate TPS65185.

    Cheers,
    Pankaj Rana
  • 0 in reply to Matt Roberts
    Prodigy 30 points

    Dear Matt, 

    For VPOS, I tried adding a small resistive load of 10K but did not get any fruitful results. Vpos comes to be 15.9V - 16V, with not significant drop. The required Vpos is 15V.

    I wonder why this is happening despite following the reference designs. Please guide me through this issue.

    Thanks.

    Best Regards,

    Pankaj Rana

  • 0 in reply to Pankaj Rana
    TI__Prodigy 730 points
    Pankaj,

    Can you provide a scope shot of the VB and VPOS startup waveforms? Also, have you tried swapping out the device on the board with a new unit?