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BQ76942: Shutdown Mode Indicator - Feedback LED

Dan@AdNav
Prodigy 50 points
Part Number: BQ76942

Hi,

EDIT: I meant FET Test mode, not shutdown mode. Sorry.

Can I please have some help with our shutdown mode indicator?
Our engineers and technicians need feedback from our BMS to prove that it it is shutdown mode, and warn them if the BMS suddenly wakes up.

Our solution was to hang an LED off one of the GPIO pins (we chose the DDSG pin, but we can change this).
However, I don't think our configuration is reliable because the LED/GPIO is manually toggled when shutdown mode is enabled or disabled.

If it's possible, how can we configure the BQ76942 to just tie this GPIO to the shutdown mode state so that we know the LED can be trusted?
e.g. we want to guarantee that while BQ76942 is in shutdown mode, the LED is on.
And we want to guarantee that while the BQ76942 is NOT in shutdown mode, the LED is off.

Thank you for your help.

  • 0
    TI__Genius 11315 points

    Hey Dan,

    If you have an available regulator, you could connect an LED to that. The regulators can be programmed to stay active in SLEEP and DEEPSLEEP mode. The regulators always turn off when in SHUTDOWN mode. You'd have to make sure to edit the OTP so that the device can be configured the way you need it upon coming out of shutdown mode. 

    https://www.ti.com/lit/an/sluaa32a/sluaa32a.pdf?ts=1659718174156&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FBQ76952 

    Thanks,
    Caleb

  • 0 in reply to Caleb Perez
    Prodigy 50 points

    Thanks Caleb,

    Sorry, I meant FET Test mode, not Shutdown mode. We had problems with Shutdown mode because part of the BMS manufacturing process was waking up the BQ76942. In FET Test mode, we have all FETs disabled.

    I think I do have an available regulator. But I may have to invert the signal since we need the LED to be active while in test mode, and inactive when the BMS is operating normally.

    What I'm trying to avoid is manually toggling the LED because mistakes can be made and we need the LED to be trusted. e.g. if the LED is on, all FETs are disabled and the BMS is safe to touch.

    Is it possible to link one of the GPIO to the state of the FETs so that we aren't making manual changes? Is that what you're saying the regulators can do?

    Thanks,
    Dan

  • 0 in reply to Dan@AdNav
    TI__Genius 11315 points

    Hey Dan,

    The regulator solution I suggested was really only applicable if you were testing whether the part is in shutdown mode. Why don't you just connect a resistor and LED across Pack+ and Pack-? That would be the simplest way to see if the FETs are on/if there is a current path from BAT+ to PACK+.

    Thanks,
    Caleb

  • 0 in reply to Caleb Perez
    Prodigy 50 points

    Thanks Caleb,

    If we connect an LED and resistor to the pack, then the LED will be active when the pack/FETs are enabled, but we need it active when the pack/FETs are disabled.

    We also don't want the excess current consumption. That matters to us in normal operation and in sleep/deepsleep mode, but not for the brief period of time during battery manufacture when we're using FET Test mode.

    Thanks,
    Dan

  • +1 in reply to Dan@AdNav
    TI__Genius 11315 points

    Hey Dan,

    I understand. There is no way to tie to a GPIO pin to FET Test Mode. You would need to use a microcontroller as an intermediate. 

    Thanks,
    Caleb

  • 0 in reply to Caleb Perez
    Prodigy 50 points

    Thanks Caleb :)