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BQ25570: BQ25570

Part Number: BQ25570
Other Parts Discussed in Thread: BQ25798, BQ24210, BQ24250


I am re-evaluating a design I did last year which used ST parts. Now I am aiming to migrate the design to TI BQ25570

The BQ25570 combines atleast two circuits into 1 

I am seeking your feedback on to its suitability 

I am using a 1.3W solar panel to charge a 21700 size battery 

The battery spec is 3.6v 4000mAh with charge voltage 4.2V

The solar panel is Vmp 4.4V Imp 295mA Isc 320mA


In the BQ25570 datasheet I see Cycle by cycle current limit of charger is typically 230mA

Which fits in nicely given the variability of solar energy across the year( I'm in New Zealand)


Is the BQ25570 best fit ?

I am considering also BQ25540 but not so sure its the best fit

We looking at volumes 1000per year at least 


You recommendations are welcome especially given I in time critical design phase 

  • Hi,

    The BQ25570 is boost only charger.  Since your solar panel has MPP at 4.4V and your battery voltage is 4.2V, the charger would eventually not be boosting and there would be a path from VIN_DC to BAT when V(BAT)=4.2V, through a diode.  If you boost up the panel slightly to 4.5V and then connect the battery to the buck converter output set to 4.2V, that might work but only give 100mA of charge current.  For a such a large battery, I think you need fewer losses to get max power from the panel.  Since VMPP=4.4V is so close to VBATREG=4.2V, you could use the linear regulator based BQ24210 with minimal losses.  BQ24250 with external VINDPM=MPP resistors is another option.   But neither the BQ24210 nor BQ24250 periodically samples the panel open circuit voltage for most accurate MPP measurement across brightness.  Also, both of those chargers have safety timers that would time out before the low charge current would charge the large battery.  BQ25798 is slightly over powered for your panel and requires host processor communication but would work.  



  • Thanks for feedback