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BQ25155 VIO Design for optimum power consumption

POTHIRAJAN KANDASAMY
Intellectual 600 points
Other Parts Discussed in Thread: BQ25155

Hi

We are considering to use BQ25155 battery charger IC in our design to charge a single cell Lithum polimer battery. In the data sheet I have studied about VIO pin. Instead of connecting this PIN to IO power lines of our system, we want to connect it to an GPIO PIN of CC2642 which is a BLE simplex device of TI. Connecting to GPIO will give us power advantage we believe(we can turn it off or on as we prefer to control the usage). GPIOs can provide up to 8mA in Extended-Current(EC) mode. I have following questions in this regard.

A) What is the max current drawn by VIO?(could not spot it in data sheet absolute max ratings, probably I am missing something here)

B) Can we think in those line of connecting GPIO to power the VIO? If yes please give us some application note to support the said design.

B.1) This device is also having an interrupt to inform faulty conditions.  If we power it using I/O then if there was a faulty condition (which has occurred at the time of no-power to VIO) will the interrupt and other digital-status be made available at the time of bringing back power through GPIO?

Regards,

Pothirajan.K

  • 0
    Intellectual 600 points

    Hi

    Any help in this regard is appreciated.

    Regards,

    Pothirajan.K

  • 0 in reply to POTHIRAJAN KANDASAMY
    TI__Mastermind 21590 points

    Hello,

    The VIO pin is the input to the internal level shifter in the charger. As such this is meant to be connected to the GPIO voltage rail of the MCU not the GPIO.

    A) Since this is input to level shifter, the current will be minimal in uA range. Most current will be I/O leakage current of charger which are around 1uA max for each pin.

    B) Interrupts are sent when the fault occurs. Flag registers are cleared upon read so these can be checked after power bringback

  • 0 in reply to Raheem
    Intellectual 600 points

    Hello Sharafadeen Raheem,

    I fully agree with you with respect to connecting VIO to I/O power rail of our microcontroller in a normal case. As we are trying to see alternate ways to power VIO(our GPIOs can source upto 8mA) following question arises. I am trying to understand the clarification 'B' bit clearly 

    At the time of "no power" to VIO, if there were error-events/state-change/interrupts they are maintained internally in charger chip, none of its internal functions are affected due to "unpowered VIO pin".

    During no power to VIO,  the LP(low power mode) pin interpreted as LP mode or Normal power mode?

    During no power to VIO, the CE(low power mode) pin is interpreted as active/inactive.?

    Regards,

    Pothirajan.K

  • 0 in reply to POTHIRAJAN KANDASAMY
    TI__Mastermind 21590 points

    Hello,

    To save power, you can connect VIO to a GPIO in you rapplication.

    No functions of the device will be affected if the VIO is not connected apart from the I2C communication and interrupts through /INT.

    The /LP pin has an internal pulldown resistor so the device will be in low power mode.

    /CE also has an internal pull down resistor which translates to active.

    For current consumption, the bus is normally pulled high so current is only consumed when the I2C bus pulls low or interrupt causes /INT to be pulled low.

  • 0 in reply to Raheem
    Intellectual 600 points

    Hello Sharafadeen Raheem,

    Thanks for the support. I consider all my queries are over.

    Regards,

    Pothirajan.K