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PMP30528: Inquiry about the super capacitor CVCC charger block on the PMP30528

JayG KIM
Prodigy 20 points
Part Number: PMP30528
Other Parts Discussed in Thread: TLV431

Hi. TI

I am trying to use in my project by changing the value of R/C values of the CVCC super capacitor charger part.

So, Please advise on how to adjust the resistance value as following schematic condition.

Thank you

JayG

  • 0
    TI__Mastermind 40385 points

    Hi JayG,

    R6 helps set the charging current of the supercap. As the voltage increases to the desired charge voltage, the reference voltage increases up a threshold that turns ON Q3 such that the PFET turns OFF to stop charging. I recommending keeping the same threshold voltages and adjust R6, R12, and R24 with your new VBUS, Vbackup, and charge current.

  • 0 in reply to Darwin Fernandez
    Prodigy 20 points

    Hi Darwin

    Thank you for your prompt response

    According to your guide, The R6, R12 can be calculated as follows with remaining other value is fixed (R24 is fixed as 10K)

      - equation for finding R6

        . Vin = 5V, Icap = 800mA (constant)

        . Q3 Vbe_th = 0.6V (Assumed)

        . Icap = (Vin - Q3 Vbe_th) / R6.  So, R6 = about 5.5 ohm


      - equation for finding R12

        . According to TLV431 datasheet , it can be calculated as follows

        . VKA = 3.6V +- 2%, R2 = 10K, Vref = 2.5V, Iref = 1.8uA (assumed)

        . R12 = about 4.4K

        

    In conclusion, I get the above values about R6 and R12.

    Can you please review if the above value is available or not? Please your advise.

    Thank you

    JayG.

  • 0 in reply to JayG KIM
    TI__Mastermind 40385 points

    Hi Jay, yes this is the approach I would take as well to get initial component selection. Then you can fine tune it with bench testing. Thanks!

  • 0 in reply to Darwin Fernandez
    Prodigy 20 points

    Thank you for your kindly advise.