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BQ24095: Power Up Issue with no battery connected

Sean Quilliam
Prodigy 125 points
Part Number: BQ24095

I am using the BQ24095 to charge a single cell battery. 

However there is a case if the battery goes below 3V the protection circuit of the battery kicks in and shuts down the battery, effectively making it an "open circuit".  The issue with this is that when I plug in the USB cable to charge the battery the output voltage of the BQ24095 only gets to 200mV, so the battery is never charged. 

I suspect that the system circuit during power up may be drawing an excess current spike that the device thinks is a short circuit.  Unfortunately, I am not able to confirm this as the PCB layout and components don't allow me to test for this.

I have confimed by removing the battery that the BQ24095 IC is not able to power my unit by itself, even though it draws less than the 1000mA that the charger IC is set to via the ISET resistor value.  I have also changed the PRE-TERM resistor to a 10k, meaning that the pre charge current will be 1000mA as well.  

I am not able to find any information on how the BQ24095 determines if there is a short circuit or not.  There is a mention of doing a 100mA short circuit test at power up, but no specifics.  

Is there any information that you are able to provide on this please?

Many thanks,

Sean

  • 0
    TI__Mastermind 22240 points

    Hey Sean,

    Are you attempting to power your system along with the battery at the same time? Are you able to share a schematic? If the battery is seen as below the short circuit threshold (Vout(sc) = 0.8) then it will attempt to charge at the rate of the Iout(sc) value which is 15 mA. 

    Sean Quilliam said:
    I have confimed by removing the battery that the BQ24095 IC is not able to power my unit by itself,

    Is the charger supposed to be charging the battery as well as the unit at the same time? If the unit is removed will the battery charge?

    As the BQ24095 is a non-power path circuit where the battery is at the same node as the system, this can affect the output if both are being attempted at the same time as charge is not regulated to the battery separately from the system.

    Best Regards,

    Anthony Pham