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BQ76952: Multiple FETs with the BQ76952

Ivy Jin
Expert 4625 points
Part Number: BQ76952

Hi team,

My customer is evaluate BQ76952 in their new project.

They will use 14 FETs, and they requirement is 

1. CHG off time <40us(Typical 10us)

2. DSG off time <80us(Typical 40us)

They has referred the application note Multiple FETs with the BQ76952, BQ76942 Battery Monitors, but they think the off time may can't meet the requirement.

Could you please give some comments or suggestions? Or do you have any reference design can be shared to the customer?

Thanks for your support!

Regards,

Ivy

  • 0
    TI__Guru 54715 points

    Hi Ivy,

    The turn off time will depend a lot on the Ciss of the FETs used.  As shown in the apnote table 6-1 the tests used up to a combined 111 nF typical Ciss load.  As shown in the apnote to achieve fast switching a local current loop with a PNP (or P-ch FET which was not shown) will be needed with the large Ciss load.  Use a small resistor such as the minimum suggested 100 ohm to the IC pin and select individual and common gate resistors as needed.  Ferrite beads may be beneficial for individual gates as they have lower DC resistance and higher impedance at high frequency where it may be needed to suppress oscillations.  The common gate resistor in the local current loop (R35 for charge, R37 for discharge) can also be made smaller for faster turn off.  Ultimately they must evaluate if it is fast enough.