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SND9039 for 2S battery

Antony Lin
Genius 13480 points

Hi,

Considering the case to use SND9039 with 2S battery cells, we plan to generate 3.3V from a buck to supply PMIC.  For VBATSENSE power-up threshold, it's configured as 3.3V by default.  Therefore, we plan to supply VBATSENSE pin from 2S battery by adding a resistive divider in-between.  For the other power inputs (for LDO, BUCKs...etc) of SND9039, we'll still use the 3.3V from buck to supply them.

Do you see any concern about such implementation?  What's the range of the resistors (hundreds of kohm??) should be used for the resistive divider @ VBATSENSE pin?

Thanks!

Antony

  • 0
    TI__Mastermind 25805 points
    The VBATSENSE pin isn't a power pin, so using a resistive divider from the 2S battery should be ok. I recommend using resistors that give a value of 3.4 on pin to account for any inaccaracies resistors
    What will be the power up event for this system? Because VSYS and VBatsense are not tied together, there is the possibility that the sense pin will be above the 3.3V threshold before VSYS is present. I need to double check in the lab if this is ok.
  • 0 in reply to Michael Gambrill
    TI__Genius 13480 points

    Hi Mike,

    Customer considers to add some additinal circuit to make VSYS and VBATSENSE rise at the same time.  If so, do we have any other concern?

    Besides, may you help to provide the input impedance of VBATSENSE pin?

    Regarding the resistive divider @ VBATSENSE pin, is it ok to use 100kohm : 100kohm (for case of 1:1 ratio )?  Or you prefer a bigger or smaller scale of resistor value?

    THanks!

    Antony

  • 0 in reply to Antony Lin
    TI__Mastermind 25805 points

    Hello Antony,

    If they both come up and the same time or VSYS rises before VBATSENSE I do not have a concern.

    If the GPADC isn't being used, you can expect an input impedance of ~1.5Mohm.

    What voltage is the resistive divider coming down from? Two 100kohm resistors should be fine, but I will double check.

    -Mike

  • 0 in reply to Michael Gambrill
    TI__Genius 13480 points
    Hi Mike,

    They'll need to use GPADC to read VBATSENSE voltage. The input to the VBATSENSE resistive divider is 2S battery, so they prefer the ratio to be half. If so, what is the resistor value you suggests for the resistive divider?

    Thanks!!

    Antnoy