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Original question:

BQ24295: BQ24295:

BQ24295: Minimum system voltage not being respected

Rohan Hill
Prodigy 30 points
Part Number: BQ24295

Hi there,

The datasheet for the BQ24295 states: "When the battery falls below the minimum system voltage, switch-mode converter keeps SYS above the minimum system voltage."

However, in our prototypes using this IC, with the minimum system voltage left set at its default 3.5V in REG01[3:1], the output system voltage "SYS" will actually continue to fall below this and track the battery's voltage as it continues to decrease until the battery is flat. This seemingly contradicts the above statement.

Have we missed something obvious? Any help much appreciated.

  • 0
    TI__Genius 10240 points

    Hi there,

    Do you have the adaptor connected to the VBUS? Please check the VBUS voltage and make sure that the adaptor has enough power to support the SYS power, If the issue persists, please check the SW waveform and make sure the buck converter is operating. 

  • 0 in reply to ezhao
    Prodigy 30 points

    Hi Eric,

    Thanks for your reply, and sorry I didn't see it sooner.

    I am actually talking about when VBUS is not powered, and the power source is the battery itself. The datasheet suggests that in this case, the system voltage output on SYS will still be kept above the "minimum system voltage" (e.g. 3.5V), via a switching regulator.

    From the data sheet: "When the battery falls below the minimum system voltage, switch-mode converter keeps SYS above the minimum system voltage."

    Am I interpreting this wrong, and does this statement only apply when the IC is powered externally via VBUS?

    Thank you,

    Rohan

  • 0 in reply to Rohan Hill
    TI__Genius 10240 points

    Hi Rohan,

    The input of the switch-mode converter that keeps SYS above the minimum system voltage is VBUS. VBUS has to be present to maintain the minimum system voltage. This is for the application case that the system can be powered up instantly when the adaptor is plugged in even if the battery is fully drained.  

    There is a FET in between the VBAT and VSYS and no power conversion to keep the Vsysmin if the VBUS is not powered. 

  • 0 in reply to ezhao
    Prodigy 30 points

    Ok, thanks for clarifying :)