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BQ40Z50-R3-DEVICE-FW: Cannot Disable Power Save Shutdown Mode

Alex Fields1
Prodigy 125 points
Part Number: BQ40Z50-R3-DEVICE-FW
Other Parts Discussed in Thread: BQ34Z100

Hi,

I have a special application where I don't need, nor can I easily include, the voltage or temperature sense lines, but I need both chg and dsg safety FETs on.

  • I have disabled ALL PROTECTIONS AND POWER FAILURES. The DSG FET turns off after 10 seconds (I keep 100k between the input and output so that the fuel gauge will not actually shutdown).
  • The only bit set that would cause this is SDV. However, I have set Shutdown Voltage, PS Shutdown Voltage, PF Shutdown Voltage to 0mV in the Power-> Shutdown section
  • I have set POWER_SAVE_VSHUT to 0 in the Configuration-> Power config register.
  • I have read through the technical manual and this should disable the power save shutdown feature, but it is still enabled. I think the Bq40Z50-r3 Power_Save_Vshut bit does not actually disable the power save shutdown.Please let me know how I can disable this shutdown mode.

  • 0
    TI__Guru** 105870 points

    Hello Alex,

    Can you share a schematic of your system? If you don't have access to the voltages with the gauge it will not perform correctly, you will need a top of stack gauge like the bq34z100 to bypass the requirement of cell voltages.

    Power save shutdown won't be able to trigger the SDV bit, when the PWR_SAVE_VSHUT bit is set it will only trigger the PSSHUT when it the mode is triggered.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 125 points

    I am not trying to have the gauge perform correctly, I am trying to keep the FETs on, regardless of the state of the temperature and voltage sense. I thought of 2 ways of doing this, and neither work.

    1. Toggle FET_EN to disable the FETs, and manually toggle DSG_FET and CHG_FET so they stay on. This doesn't work because when the device is power cycled, the DSG_FET and CHG_FET bits are 0 on power up, regardless of what they were on powerdown.

    2. Toggle FET_EN to enable the FETs, with all protections disabled and Pwr_Save_Shut disabled. This should work, but the SDV bit is still set, and the gauge opens the DSG FET after the Pwr_Save_Shut timeout. Is there any way to disable the Pwr_SAve_Shut feature? I already have Pwr_Save_Vshut bit = 0.

    As for a schematic, I cannot post the schematic on a public forum, but I can pass along the necessary info.

    Thanks,

    Alex

  • 0 in reply to Alex Fields1
    Prodigy 125 points

    ^I also have Gauge_EN set to 0, I'm not trying to gauge, I'm just trying to keep the safety FETs closed all the time

  • 0 in reply to Alex Fields1
    TI__Guru** 105870 points

    Hello Alex,

    If you are trying to keep the FETs on at all times can you just bypass them completely?

    You can use the MCU to control the FETs with the FET_EN to turn the FETs on a start up.

    The settings you have mentioned should keep the FETs on, can you share the .gg file here?

    I sent you a request on the forum, you can send the schematic privately.

    Sincerely,

    Wyatt Keller