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LM5122EVM-2PH: LM5122EVM-2PH changes for required specification.

Radel Design Team
Intellectual 460 points
Part Number: LM5122EVM-2PH

Hello,

       I am using LM5122EVM-2PH board, for my application Vin- (22-28)Volts, Vout - 36Volts, Iout -7.5 Amps. If possible to make changes to get my Specification ?  if possible, what changes i have to do in that EVM PCB to get my required specifications.

Regards,

Akshay H B

  • 0
    TI__Guru* 78220 points
    Hi Bharath,

    Thank you for your interests. The following parts must be changed:
    (1) Feedback resistor R32: it should be changed to 1.74k.
    (2) C8, C9, C10, C11: should be changed to at least 50V rated, with same capacitance, then the loop stability would be maintained.
    (3) You may consider to change all the MOSFETs to 60V rated to have more margin, although the installed 40V MOSFET may work.

    Thanks,
    Youhao Xi, Applications Engineering
  • 0 in reply to Youhao Xi
    Intellectual 460 points

    Hi Youhao ,

           I changed Components to get 36 volts , 7 Amps output current. Board is working good. But MOSFET and Inductor is heating very badly with in 5 minutes for 200W load.

    1) How to reduce heat from those components.( Inductor and MOSFET)

    2) EVM board is working in diode emulation mode,because of that 0.8V dropping across Master high side mosfet . If i change that to forced PWM mode whether EVM board will work properly. 

    3) If changed from diode emulation mode to PWM mode what else to change to avoid switching on the High side and Low side MOSFET at a time. How to give time delay between gate drive pulse. 

    Thanking you, I am looking forward to your immediate response.

    Regards,

    Akshay H B

     

  • 0 in reply to Radel Design Team
    TI__Guru* 78220 points
    Hi Akshay,

    Glad to hear that you had your wanted output voltage. I am afraid your MOSFET and inductor selections may need to be improved. There are selection guide in the datasheet and please follow that to choose proper part. Basic ideas are:

    1. use an inductor has lower DCR. You now have higher power and higher current through the inductor. So the inductor has more conduction losses.
    2. use the FETs that balances the switching and conduction losses. You need to check both RdsON and Qg, and make a tradeoff such that the total losses are minimal.

    Hope this clarified.

    Thanks,
    Youhao Xi, Applications Engineering