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BQ76952: DSG (and CHG) FETs not activated after initialisation with BQ Studio

Jeroen Ommering
Prodigy 180 points
Part Number: BQ76952

Hi,

Using version 1.3.104 of BQ Studio, I have initialized the BQ76952 (on a proprietary board) by writing the values on the Data Memory page (by Write_All after having imported my settings, see attached  file).

After writing the DSG and CHG FETs are not activated, meaning I do not have a voltage on the Pack side. I tried applying a "charging voltage" on the pack side, which doesn't change anything. Electrically everything seems OK: cell voltages are reported correctle (I'm simulating 3 cells with a resistor network) and if I click on the "FET_ENABLE" command, the DSG FET is activated, resulting in a voltage on the Pack size. When I load the pack side with 2A, the CHG FET is activate as well, as expected. Charge/discharge current is then also reported correctly.

Looking at the registers (just after the data memory write, without any commands given in BQ Studio), I see that the XCHG and XDSG bits in the Alarm Raw Status register are set. But I don't understand why since none of the bits in the Safety and PR Alert registers are set as you can see in the snapshot below:

I would be very grateful if anyone can point out what I'm missing and what causes the FETS to remain off!

Thanks a lot for your time.

Jeroen

Attached you'll find the settings exported from the data memory page.

I also added the schematics, although I don't think the hardware is the problem.

BQ76952 schematics.pdf

1830.BQ76952_3S_30A bis.gg.csv

  • 0
    TI__Guru* 77353 points

    Hi Jeroen,

    With the device default settings, the FET_EN bit is disabled on power-up. After you send the FET_ENABLE command 0x0022, the FETs will enable if there are no faults present. By default, the CHG FET will turn off during sleep mode to save power, but you can change this in the device settings.

    If you want the FET_EN bit to be enabled by default, this can be done by programming the FET_EN bit in the Settings:Manufacturing:Mfg Status Init register and writing this value to OTP. By default, this bit is set to zero. Many applications want the host to enable the FETs initially when the system is ready.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 180 points

    Hi Matt,

    Thanks for your answer. This will work for me.

    Best regards,

    Jeroen