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BQ25172: STAT pin showing aperiodic low pulses on the order of ms

Steve Wenner
Genius 3240 points
Part Number: BQ25172

Hello.

I have the following design on a PCB and have 6 Ni-MH cells in series.  I am using a 17.3V power supply to limit the input to 18V for testing as the solar cell currently seems to run at about 20V which seems to be creating things I don't understand.  

ts goes to an MCU open collector output that is off; stat goes to MCU input; batV_monitor goes to MCU A/D input; out goes to LDO which creates 3.3V seen at the stat signal pullup.  These signals have been verified with an oscilloscope.

Questions:

I have 6 cells NiMH connected and loaded with 250mA (intentional from electronic load)....The cells are producing 6.8V.  The STAT pin is producing the signal seen below with a somewhat aperiodic low pulse on the order of a couple milliseconds.  The TS pin is a hard low (below the 0.38V expected).  Can you please tell me what is going on here and whether I am charging or not?  The datasheet does not seem to explain strange pulsing like this on the STAT pin.

If Vin is > 18V will TS go hard low (below the 0.38V)?  It seems it does.....

Thanks

Steve

  • 0
    TI__Guru* 75656 points

    Hi Steve

    Steve Wenner said:
    The TS pin is a hard low (below the 0.38V expected).  Can you please tell me what is going on here and whether I am charging or not? 

    Bill J -- Checking on this but think it is the device waking up from low power shutdown state and checking the TS pin.  NO will not be charging.

    Steve Wenner said:
    If Vin is > 18V will TS go hard low (below the 0.38V)?

    Bill J -- Yes this sounds correct, device goes into low power shutdown state, TS pin current source is turned off.

  • 0 in reply to Bill Johns
    TI__Guru* 75656 points

    Hi Steve

    Yes - The low pulse that you see on STAT pin is the device waking up from low power shutdown and checking TS pin.  Also note this is the point the unit will start operation again if the TS pin is released.

  • +1 in reply to Bill Johns
    Genius 3240 points

    Hello Bill.

    Thank you for your response.  I was wondering if you could give me an idea of what to try as I am out of ideas?

    Here is where I am at:

    STAT ---- 1 second square wave.

    TS --- 390mV

    ISET, VSET, TMR ---- 0V BUT unpowered all the resistors read as expected (see above dwg).   

    IN --- power supply set at 17.3V showing 0 current being drawn

    OUT --- connected to 6s NiMH battery pack that is reading about 4.2V

    2 Boards tested with same results.  I verified that the TMR, ISET, VSET, STAT, TS resistors values were correct.  I also shorted TS to ground in an event to toggle it per datasheet to remove any faults but to no avail.

    One more bit of info....I tried a 7.8V Lithium battery pack connected to OUT just to see if I could get charging to occur / rule out the low NiMH voltage but same result, no input current draw from power supply and square wave from STAT.

    Thoughts?

    Thanks

    Steve

    Follow up...I misread the EVM schematic wrt jumpers and had the wrong VSET and ISET resistors populated...You can see this above...

    ISSUE IS SOLVED!

    thanks for the support