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BQ76952: How to select the driving P-MOSFET (Q3) voltage and current rating for 16s battery of the Charge FET (Hardware Selection)

Meet Pandya
Prodigy 50 points
Part Number: BQ76952
Other Parts Discussed in Thread: BQ77915

Hello,

In our setup, we are using a 16s LFP battery. 

I have referred to the application note titled "Using low-side FETs with the BQ769x2 Battery Monitor Family" from Texas (SLUAA84A). In the document, the circuit mentioned for driving the charge FET is attached as an image. How should we decide the voltage and current rating for driving the P-MOSFET in Part Q3? Can you please let us know which part number of MOSFET will be the most suitable for Q3? Please revert with the technical clarification for the selection of the MOSFET.

Thanks and Regards, 

Meet Devendra Pandya

  • 0
    TI__Mastermind 27830 points

    Hello Devendra,

    You can use a high-voltage signal-level P-Channel FET for this FET. The voltage rating depends on how negative the PACK- voltage could get when a large charger is attached. In our designs we've used high-voltage rated. The current should be really low (in the mA range at most), so current capabilities should not be much of a concern.

    We have reference designs (like the TIDA-010216) and other devices (like BQ77915 or BQ769x0) that use these type of FETs if you need some reference.

    There is also some detailed discussion in an application note from an older device family (The BQ769x0) that may be useful. See Section 6 FET Drive in the bq769x0 Family Top 10 Design Considerations application note.

    Best Regards,

    Luis Hernandez Salomon