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PMP8740: Auxiliary Power Section

Chethan S
Prodigy 60 points
Part Number: PMP8740

What is the maximum Current(for whole circuit) rating of VCC_FB(12V@?A)?

Since we are using single VCC_FB power supply for PSFB IC, 4-Driver ICs and others bucks conversions like Buck +5V, -5V and +3.45V.

And what is the Primary Mosfet Driver ICs(Both) current at output no-load?

Please help me...

  • 0
    TI__Expert 5925 points

    Hello Chetan,

    You can download the design consideration of PMP8740 at the following link:

    https://www.ti.com/lit/pdf/slup348

    On page 15 there is a table showing the power consumption of all main blocks; so in total the auxiliary PSU supplies ~ 9.5W. 

    In the specific case, for the 12V_FB, it's circa 8.5W maximum (fan at maximum speed). The primary side MOSFET drivers, when not switching, consume ~ 0.4 mA each, therefore total 0.8 mA * 12V = 9.6mW. When they are switching, then you should consider the power needed for all drivers (pair PNP + NPN for each FET), charging and discharging each gate capacitance, and the loss due to magnetizing current of the two gate drive transformers T2 and T3.

    Please let me know if you have more questions.

    Thanks,

    Roberto

  • 0 in reply to Roberto S.
    Prodigy 60 points

    Hello Roberto,

    We are working on the same 32V@60A reference design.

    We are only working on PSFB(with driver section) section only by giving external 12V from DC supply in no voltage at DC Input. 12V DC supply consumes around 70mA.

    When we increase PSFB DC input voltages to around 40V to 80VDC, 12V DC supply consuming around 120mA to 200mA. And Mosfet gate pulse waveforms get distorted around 40V to 80V.

    Above conditions without Fan

  • 0 in reply to Chethan S
    TI__Expert 5925 points

    Hello Chethan,

    Are you using the same MOSFETs like in PMP8740? Also, same gate drive transformers?

    If you have a thermal camera, you may want to take a picture at 80Vin, where the driver section consumes 200mA.

    You should see something getting hot; please try to understand what is getting the most power consumption.

    Thanks,

    Roberto