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BQ76930: DSG/CHG signal falls down during activation

pebl97
Intellectual 290 points
Part Number: BQ76930
Other Parts Discussed in Thread: BQ76200, , BQSTUDIO

Hi Team,

I I'm evaluating a BMS design constisting of bq76930+bq76200 for 10s battery.

Here the schematic of the AFE and powerstage:

       

During activation of a capacitive load (680µF caps of an engine controller) the DSG and CHG signals of the AFE get low. I also see a short communication failure via bqstudio during the activation process.

So it looks like the AFE will reset for a short time (after 360ms).

I already checked the voltage at VC10X, VC5X, REGSRC, VDDCP at the moment, when DSG falls down, but all of them are stable.

At the beginning of the activation the voltage at VC1 falls down to 1.88V. Is this the reason for the reset? Will increasing the input caps for the filter (C14 - C24) helps? 

 

The voltage at VC5X and VC10X looks stable for me:

VC10X                                                                                VC5X

                               

Any other signals I should capture for research?

BR, Patrick.

  • 0
    TI__Guru 54715 points
    Hi Patrick,
    The waveforms show a 150A current surge, that sounds like a short circuit. It may be a protection event with recovery by the gauge. Check the settings or ASCD and AOLD in the gauge, these are sent to the bq76930 for fast response. Look at the CHG and DSG from the bq76930.
    Some of the schematic grounds show with GND, some do not have that text. Be sure there is no significance to that difference and that all are connected and do not move independently during the transient.
    If REGSRC is stable the outputs should be OK, but check REGOUT to be sure it is stable, and if relevant check VCC at the gauge.
    If the AFE is getting reset it would end up in ship mode. The input voltages look/sound OK.Larger cell filter caps are unlikely to help. A short circuit is a normal protection event and the system should react to it, a loss of communications during protection or transient is not expected with the high side switch. Check the SMBus signals to see if they are getting disturbed.