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BQ76200: Control exception with BQ76952

Cherry Zhou
Mastermind 22235 points
Part Number: BQ76200
Other Parts Discussed in Thread: BQ76952, , EV2400

Hi team,

The BQ76952 and BQ76200 are directly connected. The battery is a 48-V system. When these two devices are connected, approximately what is the high level of DSG_EN,CHG_EN? Could you help share some test waveforms?

When customers use the power supply to test these two signals, they will increase with the battery voltage. Connect to EV2400 control, VBAT is 30V, DSG_EN and CHG_EN signal are approximately 20V. BQ76200 output is abnormal. CHG, DSG signals are small duty cycle switching signals. Here is the schematic: 

Could you help check this case? Thanks.

Best Regards,

Cherry

  • 0
    TI__Mastermind 42060 points

    Hello Cherry,

    Why are they using the BQ76952 with the BQ76200? The BQ76952 has integrated high-side N-Channel FET drive, so the BQ76200 is not necessary. Are they connecting the DSG/CHG pins from the BQ76952 to the BQ76200? This would not be good.

    DSG_EN and CHG_EN at 20-V is already above the absolute max ratings for the BQ76200.

    The recommended voltage for these pins is shown in the datasheet:

    The digital high for these pins (The voltage when DSG_EN is high and active), is also mentioned in the datasheet, this voltage is 1.2-V. If they want to use the BQ76200 with the BQ76952, they would need to use the DDSG/DCHG pins to drive the enable pins.

    I still would not use the BQ76200 with the BQ76952, since the device has integrated high-side FET drive.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    TI__Mastermind 22235 points

    Hi Luis,

    Thank you for the support.

    Could you help tell how many N-MOSFETs does the BQ76952 support in parallel? The previous design was for the BQ76952 to have insufficient drive power when multiple MOS are in parallel. 

    Thanks and regards,

    Cherry

  • 0 in reply to Cherry Zhou
    TI__Mastermind 42060 points

    Hello Cherry,

    There is no set limit, usually only the turn-on/off times are affected. 

    However, we have tested up to 24 MOSFETs (12 CHG/12 DSG FETs in parallel). See our Multiple FETs with the BQ76952, BQ76942 Battery Monitors application note. The FET driver of the BQ76952 should be sufficient in most cases, if the turn-off is too slow, we show a local turn-off circuit in the application note I shared to speed-up the turn-off of the FETs.

    Best Regards,

    Luis Hernandez Salomon