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BQ24253: solar charger and power path management

user5914470
Prodigy 30 points
Part Number: BQ24253

Hi

I am planning to use the bq24253 as standalone solar charger with power path management.

Setup : LiPo battery - 6V solar panel - buck converter ( to 3.3V ) - ( A solenoid is activated every 30s )

1) In the document "Using bq2425x's DPM Feature for Solar Panel Applications", I understand that the transistor between the BAT and SYS output is used in order to power the load with the battery when the solar current produced is unsufficient (LDO). What would be the transistor specifications ?

2) I previously used the MPC73871 IC from Microchip based on the design of the solar charger from Adafruit. They use a huge capacitor (4700uF) in order to stabilize the charger as the current of the pannel can drop very quickly. Is it still necessary to add this capacitor with the bq24253 setup ? (cdn-learn.adafruit.com/.../projects_solarv2.png

Thanks in advance for your answer

  • 0
    TI__Guru**** 165886 points
    Hi,

    Regarding 1, the RDSon of the FET between BAT and SYS is the last entry on the elec spec table at bottom of page 10.

    Regarding 2, such a large capacitor is not needed; however the minimum recommended capacitor per the datasheet and/or app note is needed. The charger uses its VINDPM loop to regulate its input voltage in order to prevent collapsing the panel. When using the BQ24253, I recommend shorting D+=D-, EN1=high, EN2=lo and size the ILIM resistor slightly higher than the maximum current expected from the panel so that the VINDPM loop is always the feedback loop in control.