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Original question:

BQ25303J: Minimum Charge Current Allowed

BQ25303J: Power Path

Pietro Speciale
Prodigy 130 points
Part Number: BQ25303J

hello everybody,

For one of my projects I would like to use the BQ25303J in the typical application with external power path. I haven't found any documentation / application note relating to the characteristics that the components of the recommended pfet circuit must have (see image).
My circuit has a VBUS from 12 Vdc to 15 Vdc with VSYS at 3.6 - 3.7 Vdc with maximum output current (at 3.6 Vdc) of about 2 A (not continuous).
Are there any recommended devices / values for the PFET, diode and resistance?

I look forward to your help

Thank you

Pietro

  • +1
    TI__Mastermind 24075 points

    Hi Pietro,

        Choosing the PFET is application dependent, so we don't recommend and leave it up to the end designer. Based off of your battery voltage, you know the -VGS that the FET will be driven by when on and consequently its RDSon as well as what the max VDS would be. You know the current the FET should be rated for based off of your SYS load requirements. Using this you can choose an appropriately sized PFET for your application. 

    Keep in mind that when the adapter is present, the SYS will be driven directly from adapter input, so if you need a specific voltage rail for SYS, you would need a dc dc converter at VSYS. When adapter is absent and battery is discharged (<3.6V or 3.7V whatever your SYS rail requires) you might need to boost your battery voltage up. You will need to consider adding a buck boost IC at the SYS node.