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UCC28950: PMP8740 design chages

Nidheesh BR
Expert 1295 points
Part Number: UCC28950
Other Parts Discussed in Thread: PMP8740

Hi,

I am taking reference of PMP8740 for my charger design. PMP8740 is designed for 30V max.

So If I want to upgrade the voltage level to 55V is there any changes to be made on the precharge circuit shown in the figure(Changed the precharge MOSFET)?

Like any rating changes for these components needed?

  • 0
    TI__Genius 13660 points

    Hi Nidheesh, an expert will get back to you tomorrow.——Teng

  • 0 in reply to Teng Feng
    Expert 1295 points

    Ok theng

    Thank you.

  • 0
    TI__Expert 3460 points

    Hi Nidheesh,

    Sorry for the replied late. I think you have to make new turn rate of  the transformer and change SR mosFET and ORing mosFET to high voltage stress mosFET. for the pre-charge circuit, I don' t think you have to change to the value.

    thanks

  • 0 in reply to Bliss Zhou
    TI__Expert 5875 points

    Hi Bliss,

    Thanks for answering quickly to Nidheesh's email.

    Hi Nidheesh,

    Bliss is right, you have to adjust the main transformer turns ratio and change the SR FETs to higher voltage.

    In theory there is no need to change any component in the pre-charge circuit, because Q32-A&B are rated @ 160V and to the transistor Q33 will be applied worst case -Vout_max / 2  (so -27.5V, due to the voltage divider RT1 and RT2) in case there is a reverse polarity connection.

    By the way, if Vout_max is 55V insetad of 32V, the dissipation on R83 would be too high.

    For this reason, I suggest also to modify R83 from the original value of 1 KOhm to 4.7 KOhm.

    Best regards,

    Roberto

  • 0 in reply to Bliss Zhou
    Expert 1295 points

    Hi Bliss & Roberto,

    Thank you for your valuable suggestions.

    As both of you said, I updated the transformer turns ratio and SR MOSFETs.

    While trying the precharge circuit, once it is worked and after that, it got failed(one precharge MOSFET got failed, I am using BSC027N10NS5). 

    That's why I doubted the rating of precharge circuits. I will update the change that you suggested and proceed.

    Thanks.

    Nidheesh.

  • 0 in reply to Nidheesh BR
    TI__Expert 5875 points

    Hi Nidheesh,

    Another important thing is the timing, while you enable the DC/DC converter and the pre-charge circuit.

    The voltage on C57 (which is the floating voltage, needed to drive all pre-charge FETs) should be already stable and at its nominal value before you enable all FETs; if not, the voltage on C57 might be insufficient and all FETs are driven in the linear region, which leads to fail if a load is applied to the charger.

    So, again, please check with a scope, that before you enable all FETs the voltage on C57 is well above the gate threshold voltage: I would suggest it should be at least 8V...10V, best if 12V.

    Best regards,

    Roberto

  • 0 in reply to Roberto S.
    Expert 1295 points

    Hi Roberto,

    When I have tested for the last time the voltage on the C57 capacitor is like 12 V if precharge no enable signal and 9V if precharge enable signal is given from the controller.

    But after replacing R83 with 4.7K now the c57 voltage seems to be 12V after and before the precharge enable . But I have to power up DC-DC and test the reliability.

    Thanks.

    Nidheesh

  • 0 in reply to Nidheesh BR
    TI__Expert 5875 points

    OK Nidheesh,

    That makes sense to me. Just let me know how it goes.

    Regards,

    Roberto

  • 0 in reply to Roberto S.
    TI__Expert 3460 points

    Nidheesh,

    since we didn't hear your replied long time. I guess you solved your questions. I will close this thread. if you have more questions, please feel free open this thread or you can create new thread to discuss.

    thanks