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BQ25302: ICHG at 1A, external source limited at 0.5A

Ue
Genius 16285 points
Part Number: BQ25302

Hi all

My customer has this question for the BQ25302:

What happens if the ICHG is set to 1A while the external source is limited to 0.5A ?

Best regards

Ueli

  • 0
    TI__Mastermind 24075 points

    Hi,

       What do you mean by external source? Input source?

  • 0
    TI__Genius 16285 points

    Hi Kedar

    Correct, the customer refers to the source connected to VBUS.

    Best regards

    Ueli

  • +1 in reply to Ue
    TI__Mastermind 24075 points

    Hi Ueli,

       Based on calculation, you would run into regulation by the input source at higher duty cycle, so when the battery voltage approaches close to charge regulation voltage. This would not be affected by the IINDPM of the BQ25302. Instead, the input voltage of the supply will begin to droop as it tries to supply output power, and eventually the input voltage will droop till it hits the VINDPM threshold, after which the input voltage regulation loop will kick in. In VINDPM the charge current will be reduced to maintain the input voltage at the VINDPM threshold to prevent brownout.

  • 0 in reply to Kedar Manishankar
    TI__Genius 16285 points

    Hi Kedar

    Thank you for the clarification. 

    Do I understand you correctly that having a 0.5A current limited input sourced this shouldn't be a problem ?

    Best regards

    Ueli

  • +1 in reply to Ue
    TI__Mastermind 24075 points

    Hi Ueli,

       It wouldn't be a problem, but that doesn't seem like a good design to me. If the charge current cannot be reached, you will be forcing the charger to charge the whole time in VINDPM regulation loop due to the current limit of the customer's input supply. Changing the resistor from ICHG to GND will modify the charge current so it is easy to reduce the charge current. Again, to reiterate it isn't an issue as your termination will occur when not in the VINDPM loop as  charge current would have tapered below the input adapter supply current limit so there will be no issues.

  • +1
    TI__Genius 16285 points

    Kedar

    Very good, thank you for the clarification !

    Best regards

    Ueli