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BQ25505: Component Recommendation for Small Solar Panel Charging of Li-Ion 18650

James Ries
Prodigy 40 points
Part Number: BQ25505
Other Parts Discussed in Thread: BQ24210,

I will be using a relatively small solar cell to charge a Li-Ion battery.  My application is tolerant of slow charging.

Solar panel: 5V (6VOC), 30mA-34mA

Battery: 18650 3.7V 2200mAh, no thermistor

This is a simple application with no need for monitoring functions.  Just basic charge management and battery protection.

I've been looking at the BQ24210 solar charger and BQ25505 boost charger.  The 24210 is easier and less expensive to implement.

Does anyone have a recommendation for which part to use, or another part that would be better?

  • 0
    TI__Mastermind 20570 points

    Hello,

    The abs max rating of VIN on the BQ25505 is 5.5V. With Panel VOC equal to 6V, it is exceeding the max rating of the device. You will need to add a voltage clamp at the input of the BQ25505.

    On the other hand, the BQ24210 is a linear charger, which the input needs to be higher than the output voltage. Based on your lighting condition, the output voltage and current of the solar panel varies. In weak light, the output voltage of the panel can be less than the battery charging voltage, then the charger will stop working.

    Also, there is a safety timer built in the BQ24210 which is at fixed value. Since your battery is relative large. It will take a significant long time to charge this battery with only 34mA max input current. The safety timer will be triggered.

    Moreover, the minimum output current regulation value on BQ24210 is 50mA. Therefore, with charging might not be terminated correctly. 

    Therefore, BQ25505 with external input clamp might be your best option here.