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BQ25703A: Adapter current limit changed on the fly?

Allen Wachter
Expert 6730 points
Part Number: BQ25703A

For the BQ25703A can the host change the parameters for the adapter current limit on the flyway while the charger is active?

Also, this is for a SuperCap application.  Do you have any application circuits for SuperCap charging?

Thanks

  • 0
    TI__Guru 56650 points
    Yes. BQ25703A adapter current limit can be changed while the charger is active.
    Recently, I see a supercap application. What is the charging voltage and capacitance?

    For a Li-ion battery, the precharge current is clamped at 384mA with 10mohm sense resistor. Right now, I recommend reducing the charging sense resistor value to have a higher initial charging current for super cap application. For example: if change the sense resistor to 2mohm, the initial charging current at zero volt capacitor voltage would be 384mAx1.9A.
    BTW, please select a big package BATFET to support 1.9A working at linear mode.
  • 0 in reply to Wang5577
    TI__Expert 6730 points
    The application is 5Vin (from USB or adapter) charging two supercaps in series with an effective capacitance of 12.5F at 5.7V.

    My concern here is that we will be operating in LDO mode for most of the charge cycle (up to 3.6V?). They have a limited amount of source current available when operating from USB and would not like to waste power in LDO mode.

    Is there anyway to alter the LDO mode levels so the device will start switching at lower output levels?

    Thanks
  • 0 in reply to Allen Wachter
    TI__Guru 56650 points
    If BATFET is fully on, it would not waste power in LDO mode. To make BAFET fully on early, we need to lower down the minimum system voltage (Vsys_min) setting.
    Two parameters are related to this Vsys_min setting:
    1. The BATFET is a PFET. The lowest Vsys_min setting is depended on the BATFET fully turn-on voltage.
    2. Minimum system operating voltage: If Vsys_min setting is too low, the charger can still work after receive the command. But, the system operation may stop until the charger bring the output voltage up.