• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 62 subscribers
  • Views 94 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

BQ25895M: battery is 4.2V，what if I don‘t change the default value of charge voltage？

BQ25895M: Issue charging a flat battery (battery iinternal protection circuit has isolated it )

David Guest1
Intellectual 340 points
Part Number: BQ25895M
Other Parts Discussed in Thread: BQ25895

The device fails to charge a flat `liPo battery (flat , 0V as the isolation circuit in battery has isolated the battery as volage is below 3V).

The datasheet says it puts 100mA into a shorted battery - but I findd= that strange as there is no voltage at all present across the battery (should a voltage there even if ther is not battery)

So it charges perfect a batery that hasn't gone into protect mode (aka above 3V) no problem - but doesn't even try when battery has gone to 0V?

Is there a fix ?

  • 0
    TI__Mastermind 22245 points

    Hi David, 

    Thank you for reaching out via E2E. Please see my comments below. 

    The BQ25895M attempts to charge a battery at 100mA anytime the voltage at BAT pin is < 2V. You mention the device fails to charge your liPo battery when isolation circuit is enabled. What is the required trigger for the isolation circuit to reconnect the battery to the charger?

    If charge is enabled the BQ25895M should attempt to charge at bat pin even if nothing is connected besides the required output capacitor. 

    Best Regards,

    Garrett 

  • 0
    Intellectual 340 points

    Thanks for your reply. 

    Without a battery fitted and with chip powered (supplying power to design), there is no voltage across the battery capacitor. 

    Just in case my chip is a BQ25895, without M suffix.

    Is there any register bits that could disable supplying power to battery at 0V.   

    It works perfectly if battery when battery hasn't isolated , aka 3V and above.

  • 0 in reply to David Guest1
    TI__Mastermind 22245 points

    Hi David, 

    David Guest1 said:
    Without a battery fitted and with chip powered (supplying power to design), there is no voltage across the battery capacitor. 

    Do you by chance also have the NTC thermistor, which connects to TS pin, removed when no battery is connected? With no NTC connected the BQ25895 and BQ25895M will have a TS fault and there will be no voltage at BAT pin. 

    I have confirmed in lab on the BQ25895EVM with all default register setting that with no battery connected device will provide power to BAT pin as long as there is no fault condition. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Intellectual 340 points

    No the NTC isn't fitted on this particular design - we do have it fitted on ther designs. Also it doesn't explain why when the battery is connected it charges perfectly, butt then won' charge if its allowed to go flat.

    So it could be we accidentally writing to registers or a fault exist.

    What faults would thee be so we can reverse engineer and potentially ensure all I2C transactions are done to ensure any fault is cleared and so it should return back to charging.

  • 0 in reply to David Guest1
    TI__Mastermind 22245 points

    Hi David, 

    David Guest1 said:
    Also it doesn't explain why when the battery is connected it charges perfectly, butt then won' charge if its allowed to go flat.

    Please help to share a full register read at the time when 'flat' battery will not charge. For this register dump please help to turn on ADC feature via REG02 bit 7 = 1 before reading all registers so we can review all available status information. Status registers should help to identify any potential fault occurring. 

    Best Regards,

    Garrett