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STAT Pin BLINK state

Marek Jaworski
Prodigy 20 points
Part Number: BQ25176J

Tool/software:

Dear TI engineers,

I am developing a device which will be able to charge a single cell Li--Ion battery to 4.2V. I followed the application notes and created such circuit:

For simplicity let's assume that Transistor Q4 is always closed and output "VBatt_4V2" has no load, the battery is not connected.

I wanted to connect the STAT Pin to microcontroller's (further known as "uC") input pin to provide the information about charging status to the system. The uC is also powered by 3V3 net.
In order to trigger the fault condition I shorted "VBatt_4V2" to GND for a brief moment. Then I found out that despite blinking diode, the uC doesn't detect the signal change.
I connected the oscilloscope to the same point where I connected a wire between STAT Pin and uC input and measured the amplitude of blinking signal. I provide the oscillograms below:

Let's skip the discussion about duty change during fault condition. The problem is that the amplitude of a signal is around 1.8V which is too low for my uC to detect a "High" state.
The "3V3" net has constant 3.3V during operation.
I recreated the observation on 3 different boards, all had the same outcome - too low amplitude of high state.

Could you please let me know whether I made a mistake during development or is it some undocumented feature of the battery IC itself?
Kind regards
Marek Jaworski.

  • +1
    TI__Guru* 75486 points

    Hi Marek

    The voltage drop across the LED D14 may be causing the low voltage uC is seeing.  You could try adding another pull up to the STAT pin to increase voltage.

  • 0 in reply to Bill Johns
    Prodigy 20 points

    Dear Bill,
    holy hell, you are right, I made an elementary mistake! Although I can't simply add another pull-up resistor, I came up with a different solution:

    Thanks to such STAT circuit, the diode will be able to turn on, and the "Aku_Stat" High logic level will get around 3V.
    Case closed, thank you very much for being my debugging duck.