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BQ25895: Charger for high discharge 18650 li ion battery.

Siddhesh Peshkar
Prodigy 160 points
Part Number: BQ25895
Other Parts Discussed in Thread: BQ27742-G1, CSD87313DMS, BQ40Z60, BQ24266

Hi,

i have been working on an application which involves a high discharge 18650 li ion battery. The battery being rated for 4A charge and 10 A discharge, it would be wise to make a charger with similar specs. Apart from that, the function of battery SOC would be desired.

So the total functionality would include

  • A charger
  • A fuel gauge
  • battery protection

I went through ti product portfolio and found bq25895 can serve my purpose, only that i doesn't have a fuel gauge, which is not big an issue as a discrete fuel gauge IC can be used for that function. The datasheet for bq25895 says a continuous discharge of 6A while a pulsed discharge of 9A ( till 1 sec ) as permissible range, after which it runs into cutoff by turning off the integrated discharge mosfet.  So approach 1 includes a bq25895 ( charger + protection ) and a discrete fuel gauge ( preferred due to less footprint area) .

Another component i have found out from TI profile is bq27742-G1 ( protection + fuel gauge + external CSD87313DMS mosfet ) and then i need to find a charger which can support upto 2.5A charging ( standalone or interface based ). This is approach 2 which includes a charger ( to be found out ) + bq27742-G1.

One more component which is in the competition and is currently being used in Alpha prototype and which makes a designer's life simple is MAX77818 from Maxim integrated which integrates all 3 of the functionality ( Specs 3A charge, 4.5A discharge and an integrated fuel gauge ). Is there any such component available from TI ?

And is there any charger available without pwerpath management. Just a 3A li ion charger for approach 2.

Or any other component with specs higher than BQ25895 for approach 1. 

Thanks in advance.

Siddhesh Peshkar

  • 0
    TI__Expert 8230 points

    Hello Siddhesh,

    Regarding approach #1, the limiting factor will still be the bq25895's overcurrent protection and the abs max continuous current of 6A. The protection device chosen must also accommodate the high discharge current of 10A (I'm under the assumption the application requires 10A continuous discharge current). In order for the bq25895 to be used, an external FET (most likely a low RDSON PMOS) can be added between SYS/BAT to provide a discharge path with a higher current tolerance.

    The MAX77818 still has the same limitation for maximum discharge current (in this case lower than the bq25895 at 4.5A vs. 6A). We do have the bq40z60 which is a BMU that integrated a switching charger plus gauge/protection.

    I also recommend reviewing the bq24266 charger, which is a powerpath controller that also allows you to add an external FET to allow for higher discharge currents, the BGATE pin controls the gate of an external PMOS.