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BQ76952: Standalone mode, how to test FET settings before performing OTP?

AJ
Prodigy 60 points
Part Number: BQ76952

Hi,

We are building some standalone battery packs (i.e. no host MCU) and using the BQ76952 as our battery monitor. One key requirement for us is that both FET's MUST be enabled on init (i.e. as soon as the battery pack is assembled). I have two main questions:

  1. What settings do I need to write in order to tell the BQ76952 to enable both FET's on init?
  2. Before performing OTP to write that setting permanently, I need a way to confirm that it works. Is there a way for me to "simulate" init conditions on the BQ76952 without deleting that setting from the RAM region?

In other words, I would like to be able to configure that FET enable setting in RAM first. Then perform some sort of command sequence (with bq studio for example) to have the BQ76952 mimic an init cycle so that I can confirm that in fact the FET's got enabled right away without any host MCU commands. I've tried sending a reset command but that completely deleted all my RAM settings. I've also tried sleep and deep sleep modes but that didn't work either.

We are facing an imminent deadline to get this working so your prompt reply would be greatly appreciated.

Thanks,

Aamer

  • 0
    TI__Mastermind 42060 points

    Hello Aamer,

    AJ said:
    What settings do I need to write in order to tell the BQ76952 to enable both FET's on init?

    You can read Section 13.3.6.1 Settings:FET:FET Options of the TRM for details. But you'll want to set(1) the FET Options[FET_CTRL_EN] bit and clear(0) FET Options[FET_INIT_OFF]. By default FET_CTRL_EN will be cleared unless OTP'd.

    The timings for the initial wake-up can be seen in Section 16.4 Startup Timing of the datasheet.

    AJ said:
    Before performing OTP to write that setting permanently, I need a way to confirm that it works. Is there a way for me to "simulate" init conditions on the BQ76952 without deleting that setting from the RAM region?

    Not without OTP'ing the device, unfortunately. On RESET() or waking from SHUTDOWN, the part will start with the OTP settings. I believe DEEPSLEEP may be the closest power mode that will do what you want. You can try testing it with both settings and see if there's a difference.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 60 points

    Hello Luis,

    The default settings for those two bits that you mentioned are already configured as you describe:

    • FET Options[FET_CTRL_EN] bit is already defaulted to "1"
    • FET Options[FET_INIT_OFF]  bit is already defaulted to "0"

    However, the FET's are not enabled right away on startup. I've confirmed that these are the default settings from the TRM as well as reading their values using BQ studio.

    Furthermore, I think another person was asking about the same thing and it looks like you gave him a different answer (different configuration register/bit). Please see this thread discussion:

    https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1292358/bq76952-enable-chg-and-dsg-fets-on-startup?tisearch=e2e-sitesearch&keymatch=bq76952%2520fet#

    So what is the correct configuration to set such that the FET's are enabled automatically on init (when the battery pack is assembled) without requiring a "fet enable" command to be sent from an MCU?

    I've also tried toggling deepsleep yesterday and that does not appear to simulate the init conditions. I really hope there is a way for us to verify this settings before performing OTP. We can't afford to OTP because if we get it wrong, it means we have to discard the BQ chip and solder a new one.

    Thanks,

    Aamer

  • 0 in reply to AJ
    TI__Mastermind 42060 points

    Hello Aamer,

    Apologies there, you're right, I forgot to mention the Settings:Manufacturing:Mfg Status Init[FET_EN] bit.

    You would not able to check this without performing OTP. Now, OTP can be performed multiple times. Each register can be OTP programmed twice, while there can be 8 partial OTP writes overall. So you can OTP these settings, and if any changes for the register that you changed are required, you can OTP again.

    Ideally, you would want to ensure that all the settings are set properly, but this does allows some flexibility in case you need to program it again.

    Best Regards,

    Luis Hernandez Salomon