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Original question:

BQ76952: BQ76952

BQ76952: BQ76952 driver waveform ripple problem

Gabriel Wang1
Genius 4715 points
Part Number: BQ76952

Dear Expert

During the testing of MOS driving, it was found that the driving ripple of DSG and CHG was relatively large. Both the measurement with load (subsequent load) and the measurement without load (after disconnecting the load) were the same. Moreover, the waveform of the bootstrap capacitor from CP1 to BAT was normal, as shown in the following figure. Please assist in analyzing the cause of this phenomenon. Thank you;
1. DSG/CHG load waveform

2. DSG/CHG no-load waveform



3. Bootstrap capacitor waveform



4. Circuit diagram

  • 0
    TI__Mastermind 42060 points

    Hello Gabriel,

    It seems that they are not using these pins for high-side FET drive. I'd suggest to use DDSG instead to just turn-on a pull-down FET.

    Now, the ripple may be because too much current is getting drawn by the charge-pump. The DSG pin will drive to the charge-pump voltage, this can be ~11-V above the BAT voltage. So for example, if BAT is 50-V, the charge-pump may be 61-V. 

    If we measure the current across R315, there will be a 61-V/383-KOhm = ~159-uA of current, this is enough to not be able to drive the charge-pump to its full voltage.

    Why is this set-up being used?

    Best Regards,

    Luis Hernandez Salomon