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BQ24195: STAT LED Flashing at 12 Hz when no battery detected

Victor Claver88
Prodigy 80 points
Part Number: BQ24195

Hi, 

I am having a problem with this device as it does not behave as the specifications. The LED connected to the STAT line is flashing at 12 Hz approx, rather than 1 Hz, when charging the device without a battery. I haven't found this fault on the datasheet so I would appreciate some help to find out what is wrong with the design. 

Measuring VBAT I get 4V approx, however, there is no battery connected and charging should be turned off. Any ideas? Please let me know if you need further information...

Thanks in advance. 

Best Regards,

Victor

  • 0
    TI__Expert 8230 points

    Hello Victor,

    Victor Claver88 said:
    there is no battery connected and charging should be turned off.

    Can you please verify if charging is actually disabled either by the I2C bit or the /CE pin?

    If charging is enabled and there is no battery present, what you are most likely observing is the device toggle between the "Charging" and "Charge Done" states due to the decoupling cap on BAT charging to the VREG threshold and then discharging to the recharge threshold. 

    Thanks,

    Fernando

  • 0 in reply to Fernando Lopez
    Prodigy 80 points

    Hi Fernando, 

    Charging is enabled and no battery present. Yes, indeed, I observe the device toggling between the "Charging" and Charging Done" states. 

    We had 2x10uF in parallel as decoupling capacitors, do you think reducing this value will help to stop that toggling?

    Many thanks! 

    Victor Claver

  • 0 in reply to Victor Claver88
    TI__Expert 8230 points

    Hello Victor,

    Reducing the amount of capacitance at BAT will only change the frequency of the toggling between Charging and Charge Done, it won't stop the behavior from happening as long as charge is enabled. If battery isn't present, we recommend disabling charge during normal operation.

  • 0 in reply to Fernando Lopez
    Prodigy 80 points

    Hi Fernando, 

    When the battery is connected and charging is enabled, the LED flashes at around 12 Hz, it seems like it thinks there is no battery connected, but in fact there is. It happens when the battery is fully charged and rather than switch the LED off it does toggle it (in fact, reading the status bits it toggles between fully charged and charging), which does not seem right. Any ideas why it does that?

    Many thanks in advance. 

    Best Regards,

    Victor 

  • 0 in reply to Victor Claver88
    TI__Expert 8230 points

    Hello Victor,

    Couple things come to mind:

    • Perhaps the connection between the BAT pin and the battery pack is not solid. Is this an embedded battery pack or removable?
    • The protection FETs of the battery pack are opening/closing disrupting the charging. Please verify the over-charge protection threshold of your battery pack are within the spec of the regulation voltage the bq24195 is set to.
    • The internal impedance of the cell is very high (not sure if this is an aged cell used for the testing). The cell might be charging to full and when charge terminates, the cell voltage relaxes back down to the recharge threshold. Does the toggling stop eventually if you continue charging?

    Can you share details on your application? Cell capacity, charge current, termination current, any faults reported by the device.