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System Power On/Off and BQ24251 SYSOFF

matianfu
Intellectual 500 points
Other Parts Discussed in Thread: BQ24251

We are going to use BQ24251 as portable device pmic.

According to datasheet, it seems that we can use SYSOFF to implement system power off. When external power source is not present, MCU can write this bit thru I2C to turn off VSYS output, which also drives MCU thru a separate LDO. Then all loads are disconnected from battery. When user press the power button, the gate of a high side  P MOSFET is driven low. Then battery outputs to LDO and power up the MCU. After that MCU clear the SYSOFF bit and supposedly turns on VSYS output, then all loads power up.

Will this work and is it the recommended way to implement power button and system power on/off?

Or should we leave the SYSOFF bit intact. The SYS output is available all the time if either battery or external power source is present. Then we implement power button and system power on/off logical in standalone manner.

Need some advice.

 

  • 0
    TI__Expert 7730 points
    After the device is in SYSOFF mode, clearing SYSOFF bit will not bring the IC out of this mode. Instead, an external power needs to be applied at VIN to power up the VSYS again. Can you add an external PFET between BAT and SYS and then control the gate of the FET by the power button?

    There isn't a way to force the device in SYSOFF in standalone mode.

    Thanks,
    Wenjia