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BQ24192 charger battery connected and draws more current at VBUS

Other Parts Discussed in Thread: BQ24192, BQ25892

Hi,

We are using BQ24192 in our design. The bus voltage is 12Vdc.

We configure our devices in sleep mode by turning off the charging and other peripherals supplies.

When battery is connected to the device , the device draws 15-20 mA more current at the VBUS +12V input (90mA), whereas if we disconnect or remove the battery , the current reduces by 15-20mA at the input (70mA).

Please suggest the possible root cause of this issue.

Regards,

Rajkumar Jain

  • Hello Raj,

    If charging is disabled, the device turns off Q4 (internal BATFET), but the converter remains operational in order to provide power to the load at SYS. If you want to place the device in the lowest quiescent state, you can place the device in HIZ mode. In this state, the device only uses ~50uA from the adapter and the battery powers up the system in this mode. Whenever you need to exit HIZ, if your device is in host mode, the host will need to clear HIZ when normal operation is desired or if in default mode, unplugging and plugging back the adapter should force the device to exit HIZ.

    Thanks.

  • Hello Fernando,

    Thanks for your response.

    In HIZ mode device will be powered from the battery, but in our use case the device should be powered from VBUS while it is in sleep mode.
    And battery should not be getting discharged during sleep mode so that when the VBUS is not present battery can provide longer back up to the device even in the sleep mode (i.e. some of the important interfaces are working is sleep mode)..

    Now the issue is we need lesser power consumption at VBUS (+12V) even if battery is installed in the system. As 20mA at 12V is a considerable power consumption, we need to decrease it.

    Any feedback.

    Thanks,
  • Hello Raj,

    In order for the bq24192 to enter Sleep mode, the VBUS needs to be less than the battery voltage VSleep ( typically 80mV). Assuming a fully charged 4.2V cell, VBUS would need to be ~4.12V to enter sleep mode. If VBUS is 12V, the device's quiescent current should be typically 15mA, when compared to your 20mA seems to be expected behavior.

    Since VBUS is still present, the converter is still operational even if the battery is fully charged and providing power to the peripherals in sleep mode. Please note that this current is not coming from the battery, but from the adapter, so if you have a fully charged cell it should keep its charge (assuming low self-discharge rate).

    Unfortunately for this operating conditions, with a fully charged battery and VBUS connected, the lowest quiescent current is the typical 15mA specified above. 

    I recommend reviewing the bq25892 device which offers a typically supply current of 3mA under these conditions. This device is almost pin to pin with the bq24192 with the exception that one of the TS pins has been changed to a QON pin to allow ship mode in the device and pin 24 is NC.