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BQ25886: The Power path not working correctly when battery is not connected.

PYTsai
Genius 11675 points
Part Number: BQ25886

Hi 

We got an issue that the Power path not working correctly when battery is not connected. 

With battery removed: 

1. with no load we saw below waveform at SYS pin 

2. Adding > 56mA load see the voltage drop waveform as below. 

3. waveform for adding 500mA load as below 

Would you help review our schematics below, how to fix it? 

  • 0
    TI__Genius 11675 points

    Correct the no load waveform as below 

  • 0 in reply to PYTsai
    TI__Guru**** 167086 points

    Hi PYTsai,

    Can you repeat your waveform but show VBUS and possibly IBUS?  This device has a very aggressive input OVP circuit, which causes switching to stop, and quick response after UVLO, which causes switching to resume quickly.  If there is high board trace or cable impedance, the input voltage may be bouncing between OVP and UVLO.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Guru**** 167086 points

    Hi PYTsai,

    One more question.  Is charge enabled (i.e. /CE low)?  If so, if you disable charge, do you have the same issue?

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Genius 11675 points

    Hi Jeff,

    We tested CE pin pull low and High result as below, will update VBUS and IBUS waveform later

    1. CE pin pull low, the result the same

    2. with CE pull high, the output is stable waveform as below. However in real application the CE pin is pull low, any suggestion?  

  • 0 in reply to PYTsai
    TI__Guru**** 167086 points

    Hi PYTsai,

    All of our later chargers without battery detection have this pulsing on BAT and SYS when no battery is connected.  The capacitor on BAT looks like a small battery to the charger so it charges and discharges repeatedly.  If your battery has a thermistor that is connected to TS pin and you remove the battery and thermistor, this would not happen because the charger would enter TS fault.  If you do not have a battery with thermistor, then I suggest a hardware solution that pulls /CE high when the battery is removed.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Genius 11675 points

    Hi Jeff,

    Our batter does not have thermistor, the thermistor is on board. Do you have any suggest circuit to detect if the battery is present or not, or failure ?

  • 0 in reply to PYTsai
    TI__Guru**** 167086 points

    Hi PYTsai,

    If you have a processor with ADC, can you sense the pulsing on SYS and use GPIO to pull /CE high?  If not, does your battery pressure fit into the end equipment?  Is it possible to tie the ground side of the battery pressure-fit spring to /CE so that /CE is only grounded when the battery is installed?


    Regards,
    Jeff

  • 0 in reply to Jeff F
    TI__Genius 11675 points

    Jeff,

    We pull the CE pin high. and see another issue that when the current is > 1A, the output voltage will become not stable. 

    We are using 383 ohm for RILIM. 

    Any idea where might go wrong? 

  • 0 in reply to PYTsai
    TI__Guru**** 167086 points

    Hi PYTsai,

    Can you send a scope shot of VBUS, IBUS, VSYS and ISYS?

    Regards,

    Jeff