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4 Cell Removable Battery Fuel Gauging Solution

Tom47637
Prodigy 20 points
Other Parts Discussed in Thread: BQ78PL114, BQ27505-J4, BQ27510-G1

 

 

Hi Everyone,

I'm looking for a solution that can fuel gauge a 4 Series Cell LiPo battery (10000mAh, 14.8V) and report pack information over SMBus or I2C. However the battery is removable and will be charged externally, furthermore the cell taps are not accessible. 

I've been looking through the battery fuel gauges and datasheets and the system side Impedance track fuel gauges took to be ideal, except for the 1,1-2, cell Limitations. The bq78PL114, bq20z** (60, 75, 90, 95)  also looks promising, but the cell tabs are not easily accessible. 

I was wondering if a solution exists to my requirements? Would the flash based fuel gauges work or am I going to have to get access to the series cell taps?

Thanks,

Tom.

  • 0
    TI__Genius 14985 points

    You might be able to use one of the "single-cell" Impedance Track gauges that reside on your system board like bq27510-G1 or bq27505-J4 by using a voltage divider approach as shown in this app note:

    http://focus.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=slua496

    We've only tested it for 2 series cells, but you can try it for your 4-cell application by just modifying the voltage divider ratio.

  • 0 in reply to dMax
    TI__Genius 10235 points

    Tom,

    Why do you need access to the cell tabs? Is it just for charging the battery? The problem with a removable pack being charged externally is that the FETs are off when the pack is removed from the system.  There are couple of ways around this without accessing the cell tabs.  First, you could just configure the pack to be non-removable.  Of course, the FETs would be on when the pack is removed from the system. But, this would allow you to charge through the PACK+ and PACK- pins.  Or, if you have the capability with the charger, you can send a signal to the Sys Pres pin to trick the battery into thinking it is in the system. The FETs will turn on and you can  charge the battery through the PACK+ and PACK- pins.