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Original question:

BQ76952: Low side circuit protection

BQ76952: LOW Side Switching Q3

Nick
Intellectual 672 points
Part Number: BQ76952

I am working on Low Side Power Mosfets. Highlighted line in attached snapshot is not clear to me. I understand When Charger is connected and Charge Mosfet is off then Pack- will go negative ( Vbat-VCharge).

But what is meant by "Q3 allows the gate voltage to go negative when the Cdrive is off". Please help.

  • +1
    TI__Guru 54715 points

    Hi Nitin,

    When Cdrive is low Q3 will be off and its drain will be high impedance.  It is that high impedance of the drain which allows the gate of Q1 to go negative with the source, the PACK- terminal.  See an example in figure 4-7, if the P-channel "Q3" were not present Cgate would stop at 0V and the current would continue to flow.