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BQ40Z60: Learning Cycle/Calibration mistake - Wrong current measurement

Loic Jacquinot
Prodigy 230 points
Part Number: BQ40Z60
Other Parts Discussed in Thread: BQSTUDIO

Hi,

I use a bq40z60 in a 2-cell 4100 mAh (2050 mAh/cell) Li-Po in a new custom design. My final goal is to charge it from 12V (car battery voltage) or from 24V (truck battery voltage).

- Introduction :

I had a previous design for test purpose that worked fine with both 12V and 24V input on VAC.

We needed to reduce PCB size a lot (0402 cap/resistors, etc) and integrate other parts of the system (MCU, voltage regulators, etc) on the same PCB.

I used the .srec from previous device to put in in new design.

- Problem origin :

At first, voltage and current measurement were OK with 12V charging. But when I wanted to charge it with 24V, the chip became hot (up to 55°C from bqStudio DashBoard) while on the previous design it didn't go much than 40°C.

- Mistake :

I tried to do a learning cycle (discharge) with about 300 mA load, but I forgot to disable computer auto-shutdown and I couldn't do a complete cycle. When I restrat system, current measurement was wrong (about 20mA difference from my HAMEG HM7044 supply and bqStudio) so I tried to do a current calibration :

1) I applied 12V supply on VAC, current measurement on the power supply was 300 mA (decreasing a bit while battery was charging).

2) I then entered 300 mA in current calibration and applied Gas Gauge Calibration.

3) Instantaneously, current on bqStudio and power supply where OK, but when I changed voltage to 11V, current on supply was about 450 mA while it was only 320 mA on bqStudio.

Since that current measurement is wrong even if I program it with original .srec, and it always heat up at 24V...

Is it possible to place the device in full factory settings (calibration too) ?

Thank you.

Regards,

Loic

  • 0
    Prodigy 230 points

    PS : here are my current .srec and .gg files.

    Regards,

    Loic

    BQ40Z60_Configuration.zip

  • 0 in reply to Loic Jacquinot
    TI__Guru* 76230 points
    Did you program the default srec and still see the issue. Just need to be sure what you mean by programming with original srec.

    Programming the device with the firmware www.ti.com/.../sluc598 restores it to the factory settings as long as it is not damaged. If after programming with the default srec and you still see issues, you may want to try replacing your IC.
    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 230 points
    I didn't have this default file so thank you for sharing it. I tried to import defaults data memory from bqStudio and write it to the chip, but I think it was not the best way to overwrite calibration.
    I'm not at the office right now, I'll try to flash the default srec on Monday and let you know.

    Thank you and nice day,
    Loic
  • 0 in reply to Loic Jacquinot
    Prodigy 230 points

    I have programmed the chip with sluc598 srec file, reconfigured Cell1 and Cell2 capacities to 2050mAh, Pack Capacity is so 4100mAh, minimum voltage to 4192mV with a resolution of 16, design voltage set to 7200mV, only TS1 and TS2 temperature, Term Voltage to 8400mV.

    Actually my pack is discharged : 6900 mV.
    In dashboard it is dispalyed Voltage : 6900mV, 100%, 0mA.

    I unsealed full access and enabled FET, CHG_EN and GAUGE.

    I tried to apply 12V to charge the pack but nothing happens! (about 25mA on the HAMEG supply)

    I probably missed something but can't find what. It would be fine if TI could do a default .srec for each 2S, 3S or 4S configuration with explicit documentation for each case.
    There are tons of registers that we don't know how they work, plus some are redundant like cell capacity and pack capacity, cell voltage and design voltage...

  • 0 in reply to Loic Jacquinot
    Expert 2475 points
    Using a 24V adapter voltage will increase the power dissipated by the gauge and the FETs, so this could account for some of the problem. The bq40z60 is also very sensitive to placement of external components and routing. This could contribute to the problem as well. I would compare the two layouts. The default configuration is 3S with the default srec. Fortunately, most of the parameters in the bq40z60 are cell based, so most parameters can be left at their default values. There are a few exceptions and the bq40z60EVM User's Guide provides a Quick Start guide section to help. You will have to update the cell count in the DA Configuration register, the Termination Voltage, the Minimum Voltage Output and the Voltage Resolution and you should be able to charge.