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BQ40Z60: BQ40Z60 - LED Pins not pulled low

Fred Arnold
Intellectual 680 points
Part Number: BQ40Z60

Hi,

I am using the TS1..4 Pins to drive LEDs via a FET. Same circuit as on the EV Board.

If I press the LED_TOGGLE button, it Appears the pins are not pulled low and are floating between 500mV and 1V instead of being pulled low. The LEDs remain ON.

If I press the LED_TOGGLE button again, the TS Pins are pulled high to 1.74V as expected.

On the EVAL board are the 10k Thermistors on each TS Pin which act as pull-downs. I do not have them on my board.

Is there anything I do wrong or do I really need pull-down resistors to turn the LEDs off?

Thanks,

Fred

  • 0
    TI__Guru* 76230 points
    Hi Fred,

    We will look into this and get back to you.
    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 60 points

    I was having the same issue - I do not have the 10k thermistor connected to ground.

    TSx outputs are not pulled LOW and fluctuates between 0.6V and 1.1V.

    Has this been resolved?

    Thank you

  • 0 in reply to Juwan Hong
    Intellectual 680 points
    Hi Juwan,

    The device always uses the LED/TS pins to measure the PTCs, no matter if temperature measurement on those ports is disabled or not. I would expect a firmware bug. As a result you need some sort of pull-down and the following R-C Filter to remove the PTC sample pulses from the LED. It unnecessarily brings up the bill of material but I couldn't find a way around it.

    There are only two exceptions when the temperature measurement is turned off and the ports work as push-pull outputs. Those are if the Port is configured to output ACOK or the alternative BTP signal. In this case no pull-down and no R-C filter is required and the port can drive directly the FET.

    I hope this will be fixed or documented in the Datasheet where the TS ports are described as push-pull type which might be true for the hardware but not for the firmware.

    Cheers,
    Fred