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bq34z100-G1 Behaviour when battery is removed during normal operation

Other Parts Discussed in Thread: BQ34Z100-G1

Hi,

our Gas Gauge is powered by the battery it watches and by external power supply.

I have observed a strange behaviour when the battery is removed during normal operation:

The voltage is correctly shown (slowly going down to nearly 0V because of capacitance, BATLOW gets set), but SOC stays at the last value (90%). 

Even the current doesn't change.

I would expect the SOC and current to be 0 when the battery is removed and it is the case when i send a Reset to the Gas Gauge or switch the external power off and on again. But a reset is no option.

IT is not yet enabled, but all other values are set correctly, calibration is done.

Will it work if IT is enabled?

My application must detect when there is no battery (dis)charge (no current to/from battery, even when the reason is a removed battery).

Best Regards,

Sebastian

  • Does anyone has an answer? Is it undefined how the gas gauge behaves in such a case? Do i need to check in another way if the batteries are removed and handle this special case?
  • Hi Sebastian,

    I think this should work with IT enabled or disabled so long as you have a good learning cycle programmed in.
    My experience is this works reasonably well, but I find SOC updates to be erratic.

    My application sounds fairly similar to yours in setup, and I get good functionality.
    You should post your circuit so we can have a look at the cause of the current discrepancy.
    My thoughts are most likely the sense resistor is inline with the secondary power supply path as well as the battery path? Also, what is the magnitude of the current you are talking about?

    In my application I use a 5mOhm sense resistor for ~10-20A peak currents and get a usable minimum current resolution of something like 10-20mA.

    Regards,
    Bryce
  • Hi Bryce,

    when the battery is connected the SOC, voltage and current is correctly measured/calculated.
    I have only a problem with the unchanged values when the battery is removed (but the gas gauge is still powered).
    The currents are very small, about 350mA discharge and 500mA charge. The sense resistor is a 50mOhm one and only measures battery charge/discharge. The secondary power supply is not directly connected to the battery, it only powers the gas gauge.

    Regards
    Sebastian
  • Sebastian
    Are you saying that an external supply power REGIN and the battery is connected to BAT or is there some other configuration? The device can be powered by an external 3.3V supply to REGIN and it should report the battery voltage when it is applied. It will not update the capacity when the battery voltage is restored until it runs an FCC simulation. It will run a simulation if there is a reset or if there is a charge or discharge. The gauge qill run without IT enabled, but it ill not update the Ra table or Qmax.
    Tom
  • Tom,

    the battery is connected to BAT. External power supply and battery are connected to a Low Dropout Micropower Linear Regulator that supplies the Gas Gauge with 3V3 on REGIN. So the Gas Gauge is powered when at least one of the power supplies (external or battery) is connected/switched on.

    As far as i understand it, it is the intended behaviour when the battery is disconnected to only report the voltage correctly. What about the current? I observed that the current didn't change too, which is a bit strange, but maybe this had another reason (application error). The SOC remains the same until a charge/discharge/reset occurred which is not the case when the battery is disconnected in our configuration.

    I admit that it is absolutely not the normal use case that the battery is disconnected in our device, but we try to show exact/consistent values even in such an exceptional case. And the device reported happily that the battery has enough charge and is used (getting discharged by the load resistor) when no battery was connected.

    If you have any idea how to (quickly and reliably) detect a removed battery via the Gas Gauge that would really help.

    Best regards

    Sebastian

  • Hi Sebastian,

    I have just realized that actually in our application the voltage seen by the bq34z100-g1 never actually is completely removed, as when the battery is removed the internal charger holds up the output voltage. This is slightly lower than a fully discharged battery, so the SOC monitor indicates low SOC. Sorry if my previous response was not helpful.
    We have found that the device does not behave exactly as we would like in this respect as the exact SOC indicated can vary (below 10%).

    Regards,
    Bryce