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BQ24259: Shipping mode

Magnus Jonsson1
Prodigy 100 points
Part Number: BQ24259
Other Parts Discussed in Thread: BQ25896, BQ25601, BQ24298

Hi

I planning to use the bq24259 charger in a design. When the product are used it will only be powered by the battery. When turned off the supply to all internal electronics shall be turned off. I plan to use the shipping mode for that and let the micro-controller turn of BATFET thru the I2C bus. There is a push-button that are used for power on/off and other HMI tasks. A short press shall turn it on and a long press turn it off. The button will connect both to QON pin and to our micro-controller.

Is the turn on detection on QON based on rising flank or level?

What happen when BATFET turns off thru I2C bus and QON is still high level due to our long press turn off action?

Will BATFET turn off when I2C write command is complete after stop command or before?

When BATFET turns off, the supply to the micro-controller is lost. Is there any risk to leave the I2C bus on bq24259 in a locked state when this happens?

When are power on reset performed? If battery voltage are always present, is there any power on reset when the charger is connected?

Best regards

Magnus

  • 0
    TI__Guru**** 165886 points

    HI Magnus,

    The /QON pin can only be used for exiting ship mode . You must enter ship mode using the BATFET disable bit in REG07. 

    Regarding Q1, the figure 11 on d/s page 14 shows the low to high transition plus high level for at least 2ms to exit ship mode.

    Regarding Q2, as this was not the intended operation for /QON, I will have to test in the lab to confirm operation.

    Regarding Q3, the BATFET turns off a < 1ms after the I2C write commend to REG07[5].

    Regarding Q4, all I2C communications with the charger must complete (STOP and ACK) before the microcontroller loses power.  If not, the charger's I2C engine could remain in a locked state. I recommend that the BATFET turn off be the last I2C communication to the charger before ship mode and that there is a enough capacitance at SYS and BAT to keep the microcontroller alive long enough for the communication to complete.  Later chargers like BQ25896 have another bit to enable a delay following I2C command for ship mode.  The newest chargers like BQ25601 have an I2C timer to prevent I2C lockup.

    Regarding Q5, power on reset occurs after the charger exits ship mode.

    Regards,

    Jeff 

  • 0 in reply to Jeff F
    Prodigy 100 points

    Thank you for the answers. Maybe bq24298 would be a better option for us. It seems to have the delay on BATFET turn off and also the possibility to do a hard reset.

    What happen if the QON pin receive a new valid high to low transition during the delay time between I2C shut down command and BATFET turn off moment. Will it be ignored or will it put the charger active again?

    If it is ignored, is it possible for the micro-controller to change back BATFET control bit thru I2C and avoid a shut down?

    Best regards

    Magnus

  • 0 in reply to Magnus Jonsson1
    TI__Guru**** 165886 points

    Magnus,

    We have not tested what would happen if the /QON transition occurs during the delay time and it will be difficult to do so.  I suspect it will be ignored since the BATFET is not yet in ship mode.

    In theory, the host should be able to perform an I2C write during the delay time that prevents the IC from entering ship mode.  But, again, we haven't tested that and it will be difficult to test.

    Regards,

    Jeff