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UCC24624: Parallel mosfet driver capcbility consult

Lin_Charles
Expert 4260 points
Part Number: UCC24624
Other Parts Discussed in Thread: UCC24612

Hi team,

My customer wants to use UCC25640x+UCC24624 to do 1.3kW 20V/65A application. They want to use UCC24624 to drive two parallel mosfet  in the secondside to increase the output power. Can we use this device in such application? What aspects should customer consider?

BR,

CL

  • 0
    TI__Mastermind 40070 points

    Hello Charles,

    Thank you for your interest in the UCC24624 dual SR driver.

    In general, each driver output can drive multiple MOSFETs as long as certain aspects are considered.
    The total gate charge for all parallel MOSFETs must pass through each driver output, and both outputs get that gate-charge from VDD.  The IC internal circuits also need about 1~2mA to operate, so the total power loss within the IC must be calculated.  Then use the package thermal impedance data to estimate the controller junction temperature rise. 

    Note that not all of the gate-drive power is lost within the IC, but a lot of it is.  Presumably it is powered from the 20V output, so the internal 9.5V regulator is dropping 10.5V.  If this is a fixed Vout application and you can allow body-diode rectification at power up until Vout > ~15V, then a 10~12V Zener diode can be inserted in series with VDD to alleviate some of that loss.  Of course the Zener dissipation will need to be considered, too.

    Each parallel MOSFET will need a series gate resistor to prevent high-frequency LC ringing between gates.  These may be between 5~10 ohms each, or around there.  Some gate power will be dissipated within these resistors and within the internal gate resistances of the Fets themselves. This helps to reduce the IC loss a little bit, too.  

    If Tj rise is too much for the package, consider smaller MOSFETs, if possible, to reduce gate charge.  Do not oversize the MOSFETs, since the SR controller relies on Vds regulation to 50mV anyway, so oversizing is a wasted effort. Otherwise you may need to use a separate driver (such as UCC24612) for each MOSFET pair, to spread the heat.

    Regards,
    Ulrich