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BQ25892: Input current limit question when using cascade dual charger

Statham Su
Genius 4990 points
Part Number: BQ25892

Hello Sir:

We are following the document number of TIDUC92 to do some application circuit.

When below condition, we found the MASTER charger cannot limit input current by ILMIT register.

Test condition:

VBUS input voltage was 9V, Master charger set 0.1 of ILMIT register, set 3.25A on ILMIT resistance.

Slave charger set disable input current limit, only set the charging current to 2A, bat voltage is around 4.1V

When above state, we found the input current is around 1A, it cannot limit by master charger ILIMIT register setting.

It's not the same operation with chapter 2.3 of TIDUC92.

Would you please let us know the reasons?

Please kindly provide your recommendations for us.

Thanks a lot.

  • 0
    TI__Mastermind 31140 points

    Hello, 

    The master charger (BQ25892 in your case) is not able to limit current across Q1. This FET is either fully on or off. Therefore, when you set ILIM register to 0.1A the BQ25892 will be in IINDPM status and reduce charge current to 0A in an attempt to lower the current draw, but the device is not able to directly limit the current draw through PMID to the secondary charger.

    For this application circuit it is recommended that you set ILIM on the secondary charger as well as the master charger to avoid overloading your input adapter. 

    Best Regards,

    Garrett