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Problem with designing a BMS with bq7690x

Arman Ilmak
Prodigy 10 points
Other Parts Discussed in Thread: BQ76930

Hey guys.Im designing a battry management system(BMS) with 10 3.7v 2600mAh li ion with 5 cells in parallel and 10 of these parallel packs will be in series to provide 37 to 42 volts.
I want to use bq769x0 as the controller that needs a mcu to communicate with. I have also a bms board that uses this IC.
In the IC datasheet there is a schematics that has only bat+ and GND for connecting the battry terminals and pack+ and pack - gor connecting the load.
There are to low side series mosfets named charge and discharge fets.
My question is that how can i add the charger+ and charger- to charge the battries?
In the board i have there are 3 power mosfets: one of them is connected to the charger- and the charger + is connected directly to the pack+ pin.
When there are charge and discharge fets so in the charge time i have to turn on the charge fet and off the discharge fet?
Im a little confused.
I will appreciate that if you help me guys.
Any other suggestions for a bms will help me a lot.

  • 0
    TI__Guru 54715 points

    Hi Arman,

    The battery topology in the BQ76930 data sheet is typical of a battery design, the protection FETs are in series and as long as operating conditions are normal the battery terminals are made available to the PACK terminals.  So the system sees a positive and negative, and it must provide a power path to route current into and out of the battery and between a charger and the system load. From the battery standpoint current can flow in either direction as long as conditions are suitable.

    Some system designs do want to separate the charge and discharge paths in the battery.  When this is done the system design must comprehend discharge through the charge path and charge through the discharge path as well as cycling which may occur from behavior of the battery protector.  While they are for protector devices rather than monitors, see the application notes http://www.ti.com/lit/slua772and http://www.ti.com/lit/slua910 for examples of separate paths.  With a monitor such as the BQ76930 the host MCU can decide when to turn on the charge and discharge paths so a design can have more flexibility than a protector.