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PMP30440: SN6501 VCC range doubt

David Felipe Fonseca Rivera
Prodigy 10 points
Part Number: PMP30440
Other Parts Discussed in Thread: SN6501, , SN6507

Hi, I'm looking into a 12vin/12vout isolated push pull supply and I found the reference design PMP30440 but I'm struggling to understand how the Vin can get up to 24V when the VCC range for the SN6501 is only of max 5.5V, i see that there's a diode connected  BJT on the VCC path for the SN6501 but it only must works as a reverse polarity protection right? If you guys can help me solving this doubt or suggesting other designs for my application (with available parts, most of other solutions requires transformers that I cannot find) it would help me a lot.

  • 0
    TI__Expert 5875 points

    Hi David,

    Please consider first that Q5, C4, D4, R2 and Q4 are not used, therefore C3, R1 and Q3 are connected directly to J1 (24Vin) by means of R100 and R3, which are both 0 Ohm resistors. Vdd of the SN6501 is supplied by Q3, while Vcc is kept to D3 voltage minus Vbe of Q3, therefore Vcc is actually 5V. Now, with D1 and D2 pins (internal drain of SN6501 FETs) switching between 0 and Vcc, a 5V peak-peak square wave will be applied to the gate to source voltage of Q1 and Q2 (connected in "cascode" configuration). This way both FETs can switch properly and pull down in "push-pull" topology pins 3 and 1 of T1.

    I made this cascode topology because at the time I made this design we didn´t have the SN6507, which can be use here and replace both cascode FETs Q1 and Q2 as well as U1. There is an EVM orderable online about SN6507 push-pull converter. Please have a look to the product page.

    Best regards,

    Roberto

  • 0 in reply to Roberto S.
    Prodigy 10 points

    Hi thanks a lot but I've another question, what do you mean by "Vdd of the SN6501 is supplied by Q3"? by Vdd you mean the drain of D1 and D2?
    the issue using SN6507 is that i can't find the transformer suggested in the application notes for a 12Vin/12Vout application so maybe if you can give me a hint of other transformer compatibles for such application I'll appreciated 

  • 0 in reply to David Felipe Fonseca Rivera
    TI__Expert 5875 points

    Hi David,

    Sorry, I meant VCC of the SN6501, therefore its pin 2.

    BTW there is a orderable part from Wuerth that can be used with SN6501, SN6505 and SN6507: it can be employed in 24Vin to 12Vout isolated push-pull.

    https://www.we-online.com/components/products/datasheet/750319695.pdf

    Regards,

    Roberto