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BQ76200: Mosfet drive issue for bq76200

Tino Pan
Intellectual 300 points
Part Number: BQ76200

Hi ,

My customer is use bq76200 at 12s battery pack .

After inserting the charger, the battery pack can be charged .  Then they try to close the CHG and DSG mosfet to stop charge . However, when they turned on the CHG and DSG mosfet again, they found that the CHG and DSG mosfet could not be open .
It is wrong for us to measure the wave form of the CHG and DSG pin .

  • 0
    TI__Guru 54715 points

    Hi Tino,

    I expect the waveform is the VDDCP voltage, see the application note bq76200 Beyond the Simple Application Schematic figure 4.  Common causes of a failure to turn-on with switching at 10's or 100's of Hz such as figure 5 are:

    • A small charge pump capacitor, but your rise time of the waveform looks like you have increased this.
    • Too small of resistors from the FET gate to source.  10M is typical.  If this was the issue the problem should have occurred during charge and prevented charge.
    • Too large of a PACK pin filter capacitor. 10 nF is typical.  Since the FETs switched when inserted in the charger, this may be the issue.  The charger would charge the filter capacitor and allow successful switching in the charger.
    • Too much switching loss when turning on DSG.  A few hundred ohms between DSG and the FET gates can reduce current into the PACK pin capacitor, a zener and resistor between the DSG and PACK pins can reduce internal losses. See section 4.1 of the application note.

    Switching CHG_EN and DSG_EN at separate times can help turn on or reduce the needed size of the CVDDCP capacitor.