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BQ76940: BQ76940 : Low Resistance Between REGOUT pin and Vss.

mohd imran khan
Intellectual 510 points
Part Number: BQ76940

Hi WM,

I made connections as per fig 8.3 of datasheet bq76940 for 12s configurations.

I gave boot signal of 3v to TS1 pin. After giving Boot signal i was able to observe CAP1, CAP2 and CAP3 pin voltage>3v.

I checked REGOUT pin voltage wrt Vss and i observed it to be 300mV.

i thought my source follower circuit is having some issue.

So i gave 18.8v from 5th cell to regscr.

Again i booted the device and checked volts across cap1,cap2 and cap3 >3v

REGOUT pin to vss volt was gain 300mV.

I tried checking for shorting across REGOUT pin and was able to observe low resistance of 45 ohms across this pin.

I have another working board and i crossed checked its REGOUT pin to vss resistance and i observed it to be in Mohms.

Can you suggest what can cause the regout pin to vss resistance to go low.

I hope my RCA is in right directions.

please find attach my circuit diagram with this for reference.

Thanks

Imran

  • 0
    TI__Guru 54715 points
    Hi Imran,
    The schematic appears blurry, but I don't see a problem with REGOUT. Check for a short across the capacitor or between the pin and ground, or elsewhere on the net. If a high voltage was applied to the net the IC could be damaged. Check and find the damage and fix it.
  • 0 in reply to WM5295
    Intellectual 510 points

    Hi WM,

    I checked for capacitor short at regout pin and Vss. I found 45ohms across REGOUT and Vss.

    I removed capacitor and checked for capacitor short. capacitor is found to be ok.

    46.1v is applied across FET.  please find below the voltages.

    BAT-VC10s = 15.8v

    VC10x-VC5s = 15.7v

    VC5x-Vss = 14.4v

    CAP1-Vss = 3.2V

    CAP2-VC5x = 3.2V.

    CAP3-VC10x = 3.2V.

    BAT-vxx = 46.1V

    Regout-Vss = 300mV.

    Regscr - Vss = 10v.

     

  • 0 in reply to mohd imran khan
    TI__Guru 54715 points
    Hi Imran,
    The voltages look reasonable except REGOUT. Something is loose, shorted or the IC damaged. Since it is not the cap, you might try lifting the IC pin to be sure disconnecting the IC pin makes the 45 ohm go away before replacing the IC.