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BQ24780S: /BATPRES and REGN

chentsu chung
Mastermind 6180 points
Part Number: BQ24780S

Hi Team,

Some question about BQ24780S:

1. The application is using removable battery, and we connect /BATPRES to GND. Does this has any side effect?

2. Now /BATPRES is connecting to GND, what if now remove battery?

3. In reference design, the pull high voltage 3.3V is supply from external power. The question is, the sequence of 3.3V is after SYSTEM power on, so before ACFET turns on, the SMBUS and ILIMIT can not get the pull high voltage, does this affect charger operation?

4. Follow question3, or I need a LDO supply 3.3V from AC adapter input?

5. If I use REGN as ILIM's reference voltage, then any side effect?

6. If I use REGN as SMBUS's reference voltage, then any side effect?

Thank you very much,

C.T.

  • 0
    TI__Genius 11850 points

    Hi Chentsu,

    We are looking into your questions and will reply soon.

    For now, can you please let me know your adapter voltage and the type of battery you're using?

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    Mastermind 6180 points

    Hi Angelo,

    The adapter will be 5V or 19V for the different platform, and the battery will be 1 or 3 cells Li-ion battery pack.

    Thank your very much,

    C.T.

  • 0 in reply to chentsu chung
    TI__Genius 11850 points

    Hi Chentsu,

    1) If you are not using /BATPRES, then it should be connected to GND. One side effect of /BATPRES always being low is that battery removal will no longer trigger /PROCHOT.

    2) The SW node will behave differently since there is no longer a battery to charge, but the device will still be able to operate. REGN will be active, SMBus communication will be enabled, and the BQ24780S will resume charging when the battery is plugged back in.

    3) The BQ24780S can still charge the battery without the 3.3 V pull-up rail. However, pins that use the 3.3 V pull-up will not work correctly. By the way, it's also acceptable to connect the 3.3 V supply before plugging in the adapter.

    4) You will need some sort of pull-up rail for the logic pins. This rail can be generated by a buck converter, an LDO, or an external power supply (this is what the EVM uses). However, an LDO will be inefficient due to the large difference between the input and output voltages (19 V and 3.3 V, respectively).

    5) and 6) The maximum REGN voltage specified in the datasheet is 6.3 V, which is close to the absolute max voltages for the ILIM, SDA, and SCL pins (7 V). This shouldn't be an issue for ILIM because the ILIM pin voltage comes from a voltage divider, so it won't see the full 6 V from REGN. However, I wouldn't recommend using REGN as the pull-up for SDA and SCL. You can either use a voltage divider or one of the solutions listed in 4) to generate a suitable pull-up rail for SDA and SCL.

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    Mastermind 6180 points

    Hi Angelo,

    Understand, thanks for your great help!

    Best regards,

    C.T.