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Original question:

BQ76200: To drive 24 CHG FET+24 DSG FET

BQ76200: To drive 14 CHG FET+14 DSG FET

Skate Lu
Intellectual 870 points

Part Number: BQ76200
Other Parts Discussed in Thread: CSD,

To drive 12CHG FET +12 DSG FET is OK in My PCM, But I increase the FET to 14 CHG FET+14 DSG FET, the PCM don't work.

FET I use CSD 19536KT.

And 12CHG FET +12 DSG FET is most FET bq76200 to drive?

  • 0
    TI__Guru 54715 points
    Hi Skate,
    The bq76200 does not have a maximum number of FETs, but while you can scale the CVDDCP capacitance to provide more charge into the FET gates, the resistance in the internal driver paths is fixed. Eventually you can add enough FETs that the switching is too slow to be safe for the FETs or for the pin voltages to change without collapsing the VDDCP to the UVLO threshold. It sounds like you may have reached that value. You might check your calculations on the CVDDCP size and check to see if the resistance from the DSG and CHG to the FET gate is optimized. If it is a new design, be sure the Cpack is not unexpectedly large.
  • 0 in reply to WM5295
    Intellectual 870 points
    The CVDDCP capacitance in my PCM is 10 uF.
    Is that a good value for this occasion?
  • 0 in reply to Skate Lu
    TI__Guru 54715 points
    Hi Skate,
    10 uF sounds quite capable. See the data sheet section 8.1.1.3 for the recommended ratio (23.5). You might look at the circuits and results in www.ti.com/.../slva729 and www.ti.com/.../slua794. If you have had the board/design working with 12 parallel FETs but not 14, you have likely reached the physical limit of the circuit due to the internal resistance of the IC.