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BQ24075 SYSOFF with Vo(reg) of BQ24072

Ed Walker
Prodigy 5 points
Other Parts Discussed in Thread: BQ24075

I need a Single LiIon charger like BQ24075 with SYSOFF function, but with Vout(reg) of 4.4V or Vbat+225mV.
Power path also needed like bq24075.

All the small linear chargers with; SYSOFF, PowerPath, do not have Vout(reg) low enough.

I need SYSOFF but the 5.5Vout(reg) will damage our system load.

  • 0
    TI__Prodigy 725 points
    Hi Ed,
    Looks like you're already aware of the selection table in the linear chargers app note ...
    www.ti.com/.../slua659.pdf

    As you noted, all the devices with SYSOFF are set with the system rail voltage at 5.5V. However you know that since this is a linear charger, the SYS rail will always be lower than the input, so most of the time the pass element is in dropout mode operation.

    What is the voltage of the external power source used for charging? If the system circuitry is damaged at 5.5V, I would think the external supply is set up to have lower output voltage (maybe?). Beyond that, all I can think of as an easy solution is to just follow the OUT pin (system rail) with an LDO.

    Of course this means that the LDO would be also post-regulating the battery voltage when the external supply was unplugged (and probably would be in dropout mode most of the time).

    What are the system operating requirements? If it cannot handle high input voltage (but you have a higher voltage external supply used for charging), maybe you should look at an NVDC type of power path architecture (bq2425x is our entry level device in that category).

    regards

    upal
  • 0 in reply to Upal Sengupta
    Prodigy 5 points
    Hello Upal, here is the scenario.
    I agree that the SYSOFF feature should be coupled with more VOreg options.

    1. The input voltage to the charger is between 4.5V and 4.6V.
    2. The phone chip (downstream of the charger) has an absolute max rating of 4.4V.

    Since the charger already operates as a linear regulator, it would have been nice if it limited the voltage to 4.4V or lower.

    I do not understand why we lose the regulation just because we want to have the SYSOFF function(SYSOFF is unrelated to regulation).
    It would have been best to have SYSOFF and 4.4V regulation (like the 73) or VBat +225mV (like the 72).
  • 0 in reply to Ed Walker
    TI__Expert 7730 points
    Ed,

    Currently we don't have a spin that can do all power path, SYSOFF and 4.4V Voreg. The closest path is to lower your input so that the chip is in drop out mode. The drop out is about 400mV, so maybe a simple LDO at your input can do it.

    Thanks,
    Wenjia