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BQ76940EVM: Discharge Test

Brandon Tiang
Prodigy 40 points
Part Number: BQ76940EVM
Other Parts Discussed in Thread: BQ78350, BQ76940, BQ78350-R1

I need help regarding the BQ76940EVM as I can't do a discharge of more than 10A I tried to disable all the overcurrent protection in BQ studio already.

I am trying to do 100ah battery discharge with 10-11A discharge rate, but once the discharge is more than 10A, the mosfet on BQ76940EVM just shut off.

2nd issue is the Maximum mah rating is 32767 supported by BQ78350. Since I have 100,000 mah battery bank installed,  is the best option is to set the current-scaling?

IPSCALE (Bit 15:12): Current Scale Factor
0x0 = Noted reported current and capacities are scaled by 10E0

  • 0
    TI__Guru 54715 points

    Hi Brandon,

    The overcurrent protection in the BQ76940EVM is provided in hardware by the BQ76940 IC.  The BQ78350 will allow you to disable the protection, but the hardware will still trip, so the hardware register must be set appropriately or it will turn off as you are experiencing.

    See the BQ78350-R1 technical reference manual section 3.6.1 and 3.6.2 for the AOLD and ASCD settings.  These will lead back to the registers described in the BQ76940 data sheet. 

    Yes, scaling is the approach to set a higher voltage or your specific question higher current ratings. IPScale did not work well in BQ78350-R1, this was one fix available in the BQ78350-R2 software download https://www.ti.com/tool/BQ78350-R2-DEVICE-FW. If you do not like the 10x scaling of the IPScale you can scale current yourself with a value, your system must understand the scaling you apply to the current values.  For example a 4x scaling would give more resolution than 10x and cover a capacity of about 131 Ah.  Scaling for higher current would use the same technique but in the opposite direction as the application note https://www.ti.com/lit/pdf/slua792 .  This presentation may be helpful also although it is based on a different gauge: https://training.ti.com/advanced-topics-bq40z80-current-scaling