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BQ78350-R1 + BQ76940 + BQ76200 system with Enable option

Ran Aloni
Expert 2386 points
Other Parts Discussed in Thread: BQ76200, BQ76940, BQ78350-R1

Hi all,

we consider to design a new system with offered BQ78350-R1 + BQ76940 + BQ76200 setup.
in my system there is a need to use a soft switch to close battery power supply to the load.

how would you offer to implement this system, with a soft switch?
meaning send a '1' '0' command to close / open the battery.

regards, Ran

  • 0
    TI__Expert 6085 points
    In this design, is the battery pack detachable like in generic power-tool?
  • 0 in reply to Vish Nadarajah
    Expert 2386 points

    Hi Vish,


    the battery pack is detachable.

    but still the need is to send a bit and close it even when attached.

    thanks, Ran.

  • 0 in reply to Ran Aloni
    Expert 2386 points

    Hi all,

    would you recommend, controlling the BQ76200 DSG_EN / CHG_EN pins?

    for example a bit from a uConteroller host will fix '0V' on the pin.
    attached an example.

    1) is this a valid schematic?

    2) should I add a capacitor / resistor to prevent instant high current discharge from BQ76940 pins?

    3) I don't want to use the communication line (sending 0x0022 or similar) for this, since I had the info that it may interfere with gauging and battery monitoring common work, is this still correct?

    4) other suggestions?

    regards, Ran

  • 0 in reply to Ran Aloni
    TI__Guru 54715 points

    1. it will short the CHG and DSG pins from the bq76940, this will result in a couple mA each.

    2. Resistor between the CHG and DSG pins  and the FETs above would be desired to reduce current when the FETs are on.  The bq76200 has high impedance inputs so you should have many choices in resistor selection. Since CHG is a weak pull down you may want to use a divider on CHG.

    3. Correct, you must not change I2C registers,  if there is not a bus collision the gauge will find the change and overwrite your changes.  Refer to the bq78350-R1 technical reference manual for available commands.

    4. The KEYIN input of the bq78350-R1 can be used to disable the DSG, but not the CHG.  That may be an option in some systems.

  • 0 in reply to WM5295
    Expert 2386 points
    Thanks,

    closing the DSG can be enough for us,
    I didn't think to look for the key at the Fuel gauge.