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UCC27201: When the part is not driving either the HS FET or LS FET what kind of current drains out the SW node assuming there is a 5k resistor to 3.3V and a 220k resistor to GND

Nicholas Layshot4
Prodigy 220 points
Part Number: UCC27201

Hi,

I am driving a half bridge with the UCC27201 but have a 5k resistor connected between the HS side FET source and 3.3V and a 220k resistor (a 200k plus 20k resisitive divider) connected between the HS FET source and GND. I need to know the resistance between VCC of the UCC27201 and the switch node (source of HS FET) or the current coming out of the switch node when both HS FET and LS FET are off.

Thanks,

Nick

  • 0
    TI__Mastermind 21505 points

    Hello Nick,

    Thank you for the interest in the UCC27201. Just to understand the configuration is sounds like you will have a divider connected to 3.3V, HS and ground with the 3.3V connected resistance of 5K and the ground connected resistance of 220K.

    There is a parameter in the datasheet called IHB which is the HB to HS pn quiescent current of with no switching. This parameter is tested with VHB to VHS=12V. The IHB is specified as 0.4mA typical and 0.8mA maximum. The current path will be from VDD sourcing the HB pin thru the internal boot diode, which charges the boot capacitor.

    When you initially power up VDD there will be a current path from VDD thru the boot diode to charge the HB cap, this will result in the initial HS voltage to be ~VDD minus the boot diode Vf. After the boot cap is charged, there will be the IHB flowing from VDD into HB and HS.

    Since IHB will be at a voltage likely not 12V as in the parameter table, you can review the IHB Vs supply voltage curve, Figure 21 in the datasheet for more details on the current flowing into the HB pin.

    Please confirm if this addresses your questions.

    Regards,

    Richard Herring