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UCC21520: Isolation of high side driver(i.e Operation without bootstrap)

PieterT
Intellectual 565 points
Part Number: UCC21520

Good day everyone,

I'm currently looking at the UCC21520 and have 2 questions.

1) This is more of a  double check, but in a high-side/low-side configuration, I'll be able to switch both transistors on without the device implementing any automatic protection and shutting it off. It seems so from the datasheet, just want to double check that.

2) Lastly, I won't be using this as switching, more for control. So I'll switch on the low side, then the high-side and low-side and lastly just the high-side. So These will all be switched on for a length period ~10 seconds, Therefore a bootstrap probably won't work. It can also be either for longer or shorter periods. Therefore I'd like to couple a isolated ground to the gate of the high-side mosfet, Have this coupled to an dcdc converter and couple the 12V iso output of that to the VDDA of the high side and the iso ground to the high-side VSSA. Will this work in the sense that the chip will function normally in this use case? Is there an alternate method that I could use if this might not work optimally with this chip.

Thanks in advance for any help

  • 0
    TI__Mastermind 28960 points
    Hello PieterT,

    I am an applications engineer that supports UCC21520. I will help to answer your questions.

    1) You are correct, UCC21520 can switch both outputs high simultaneously, but this is not the default behavior. UCC21520 has a configurable DT pin which must be connected to VCCI to allow both outputs to simultaneously switch high.

    2) Coupling an isolated 12V DC/DC converter with iso-GND -> VSSA and iso-12V -> VDDA should work. However, I do not understand why you would connect iso-GND to the gate of the high-side MOSFET. Normally in a high-side/low-side configuration, VSS of the high-side output is connected to the source of the high-side N-CH MOSFET. If VSSA is connected to the gate of the high-side MOSFET, what is OUTA connected to?

    Regards,
  • 0 in reply to Derek Payne
    Intellectual 565 points

    Good day Derek, 

    Thank you for the quick reply.

    1) Great so just ensure deadtime isn't enabled and I'll be good to go.

    2) I completely misspoke, I meant having the iso-12V ->VDDA, iso(ground) /Source of MOSFET -> VSSA and finally outputA connected to the gate of the highside FET.

    So in this configuration I should have no issues?

    Kind Regards,

    Pieter

  • 0 in reply to PieterT
    TI__Mastermind 28960 points
    Hello Pieter,

    You are correct, the configuration you described in 2) should work with no issues.

    Regards,
  • 0 in reply to Derek Payne
    Intellectual 565 points

    Thank you for all the input Derek, this completely solves my issues