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bq24088 evaluation module

eltury
Genius 3330 points


When using a single module the stat2 pin stays low for approximately 1-2 seconds after I remove the battery.

If I parallel 4 units (common input supply) the stat2 pins on all stay low for at least a minute after battery removal.

Why would this happen?

 

 

  • 0
    TI__Prodigy 720 points

    For one unit, it takes some deglitch time (proportional to TMR resistance) to start battery detection test.

    When BAT OUT pin voltage below 4.1V, it starts deglitch timer, for 50k TMR resistor, the timer is 350ms, after 350ms, if voltage is above 3V, it starts battery detection test.

    So it looks like one second STAT2 pin low (350ms + 125msx2 = 600ms for 50k TMR).

     

    What is the 4 units output connection? Are they in parallel?

    If just input is parallel, output connect to 4 battery pack, disconnect one battery pack should be as same as a single unit.

    If output are also in parallel, then each unit deglitch time  are different, they may fight each other.

    We do not recommend parallel output.

    For higher charge current, suggest use switching charger.

  • 0 in reply to Mao Ye35
    Genius 3330 points

    The outputs are not paralled. That would probably blow something up.

    The only thing common to the four units is the input +5volts and GND.

    I ended up putting a 1M resistor across the output terminal and the stat2 light goes out quickly.

  • 0 in reply to eltury
    TI__Prodigy 720 points

    You can watch output waveform when battery is removed.

    Normally it should jumps up a little then start to drop, when it starts battery detection, it looks like a square waveform.

    But when TMR resistor is too large, it may get triangle waveform and stay in that status.

    It may cause from current dump energy to output capacitor when battery is removed.

    If it stays above 4.1V, it will not start deglitch timer until it falls below 4.1V.

    Need detail waveforms of input pin, output pin to find the real root cause.

    Add 1M ohm resistor bleeding the energy and change the output voltage drop rate make it pass the voltage test.