BQ77905: Connecting battery's in Parallel

Nishanth M

Part Number: BQ77905

Hi,

I want to design the battery Protection. So i planned to use the BQ77905 IC. My battery Pack is 4Cells in Parallel & 3 Cells is Series. I can connect a 3 cells in series with the BQ77905 but shall i connect with that battery's in parallel. If not How i can connect the 3 sets of battery in parallel.

Battery pack Spec:TI BMS.pdf

Nominal voltage 14.40V

Nominal capacity 6.90Ah

Initial impedance 200mΩ @ 1kHz at 20°C Max.

Charge current 4.83A Max.

Charge voltage 16.80V

Max. discharge current 10.00A

Peak discharge current 20.00A

Kind Regards,

Nishanth M

over 4 years ago

0 Matt Sunna over 4 years ago

TI__Guru* 81034 points

Hi Nishanth,

For multi-cell protector ICs, you can use one IC for the 12 cells - the IC doesn't need to know how many cells are in parallel. The parallel cells will be connected together to the VC pins of the BQ77905 device. The parallel cells will be at the same voltage as each other.

When selecting the sense resistor value, just be sure to size if for the total current of the battery.

Best regards,

Matt

0 Nishanth M over 4 years ago in reply to Matt Sunna

Intellectual 295 points

Hi,

Thanks for your reply, I have attached the updated schematic, please check and tell me to go further for PCB design.

4Series & 3 Parallels

Regards,

Nishanth MBMS_BQ7904.pdf

0 Matt Sunna over 4 years ago in reply to Nishanth M

TI__Guru* 81034 points

Hi Nishanth,

The schematic mostly looks good and matches the datasheet example. One thing I notice is Q2 appears to be backwards (source and drain switched).

Best regards,

Matt

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BQ77905: Connecting battery's in Parallel