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TPS57140-Q1: how the cboot charge current flow when highside mos off?

shihui xu
Prodigy 100 points
Part Number: TPS57140-Q1

Tool/software:

can you draw the current path of the charge on the picture below? wondering how it works.

  • 0
    TI__Genius 9350 points

    Hi,

    When high side FET is off, the boot cap is charged from the boot charge regulator through the low side diode. The diode will be forward biased as the net current through it is in the opposite direction (to the output).

    Regards,

    Niranjan

  • 0 in reply to Niranjan Nair
    Prodigy 100 points

    Do you mean that this diode can pass reverse current when it is forward biased?

    Section 7.3.3 in the datasheet says that " but there may not be enough inductor current to pull the PH pin down to recharge the BOOT capacitor
    " . How does this related to inductor current?

  • +1 in reply to shihui xu
    TI__Genius 9350 points

    It is not passing reverse current as such. You can think of it as the diode becomes forward biased when HS switch is off, hence it pulls PH pin low. This is what charges the boot cap. The net current through the diode (which is dominated by the inductor current) is still in the forward direction.

    If the inductor current is too low, it may not be enough to forward bias the diode. In this case PH pin won't be pulled low and the boot cap won't charge properly.