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LM5036: what is the practical max switching frequency for 300W application

Sai Loo
Expert 4650 points
Part Number: LM5036
Other Parts Discussed in Thread: PMP40500, UCC28251

Hi team,

My customer would like to design a 54V to 12V converter with up to ~ 300W (20 ~ 25A output current) design using LM5036.

Our reference design PMP40500 is with 200KHz switching frequency. Is it practical to triple the switching frequency to 600 ~ 800KHz? (any issues with the bandwidth on the EA and current sense/limit)?

customer also asked if they could use lower voltage gate drive (6V). (with internal 7.8V Vcc, this is not possible?)

If LM5036 is not the best part for their requirement, will UCC28251 or any other part a better fit?

Regards,

SK Loo

  • 0
    TI__Expert 6080 points

    Hello Sai,

    I do not see any issue with LM5036 operating at an oscillator frequency of 1.6MHz which will set the switching frequency to 800kHz. Please refer to the graph below:

    I am not sure about the second part of your question: The Lower side gate driver LSG is powered internally by the VCC bias supply of 7.8V typ, they want to use a separate gate driver?

    Regards,

    Sonal

  • 0 in reply to Sonal Singh
    TI__Expert 4650 points

    Thanks Sonal,

    I think the concern from my customer also related to the delay time between each event.

    eg, COMP to gate drive output delay is 120nsec typical, which is more than 10% of the period if the switching frequency is 1MHz, any concern on this delay time affect the output voltage accuracy and transient load performance?

    for gate drive voltage, they are thinking of using 6V gate drive instead of 7.8V.

    Regards,

    SK Loo

  • 0 in reply to Sai Loo
    TI__Expert 6080 points

    Hello,

    In my opinion, I do not see why the compensation loop frequency would be impacted by the oscillator frequency.

    But, I hope you understand that the aux supply frequency cannot be set higher than 500kHz because there is a scope of losing the current limit due to missed blanking periods. 

    Another worry is: I have not seen LM5036 used in such high frequency because the power stage losses at this frequency will be very significant.

    Regards,

    Sonal