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BQ24195: Vbat and Vsys (figure 8)

Jacopo Agostini
Intellectual 390 points
Part Number: BQ24195

Hi,

I'm trying to understand the figure 8 in the datasheet.

When the battery is below minimum system voltage setting, the BATFET operates in linear mode (LDO mode), and the system is 150 mV above the minimum system voltage setting. As the battery voltage rises above the minimum system voltage, BATFET is fully on and the voltage difference between the system and battery is the VDS of BATFET so the Vbat is almost equal to Vsys.

When the battery charging is disable or terminated, the system is always regulated at 150 mV above the minimum system voltage setting so I don't understand why in figure in charging disable mode it seems to be regulated 150 mV above Vbat. Maybe the BATFET is still ON?

Thanks for the help.

  • 0
    TI__Mastermind 25800 points
    Hey Jacopo,

    This 150mV offset when charging is disabled is by design. When charging is disabled or terminated, the charging path is disabled, and the system is regulated to 150mV above the battery.

    This is to prevent an transition into Supplement mode prematurely, during SYS transient events.


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Intellectual 390 points
    Hi,

    thanks so when vbat<Vsys_min Vsys is regulated at 150 mV above the minimum voltage while Vbat>Vsys_min Vsys is regulated at 150 mV above battery voltage.

    I have the last question: in case I'm charging in constant voltage mode at let's say 3.9V, Vsys is equal to this charging voltage?
  • 0 in reply to Jacopo Agostini
    TI__Mastermind 25800 points

    Hey Jacopo,

    I would like to outline the conditions here just to clarify the conditions here:

    VBAT Charging VSYS
    < VSYSMIN Enabled = VSYSMIN + 150mV
    < VSYSMIN Disabled = VSYSMIN + 150mV
    > VSYSMIN Enabled = VBAT + VDS
    > VSYSMIN Disabled/Terminated = VBAT + 150mV

    To your second question, VSYS will still be VBAT + VDS until charge terminates. VDS in this case will change as the current tapers down in CV mode.

    Regards,

    Joel H