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TPS65910 SuperCap series resistor

Stephen Thomas
Intellectual 710 points
Other Parts Discussed in Thread: TPS65910

Hi,

I'm studying a schematic with TPS65910 device.Here VBACKUP pin is connected to a 1F super capacitor through a 15 ohm resistor..

1) May be this is silly ..can some one please explain me what is the purpose of series resistors mentioned in p5 (BackupBattery) of TPS65910 datasheet & what if it is not used?

2)Also can you please tell me how to calculate the Backup Time possible if only the RTC is powered from the super capacitor..Im using VBAT=5V

3)What is the difference between using a charge capacitor & a super capacitor..Im not asking abt the software configuration difference like mentioned in P12 as BBSEL=11 or 10,00,01 just the application scenario in which they are different.

Thanks for any help,

Stephen Thomas

  • 0
    TI__Expert 8795 points

    Hi,

    I have the exact same question.

    Please answer.

    /Magnus

  • 0 in reply to M.A.M
    TI__Intellectual 1820 points

    Hello,

     

    1) The resistor specified is the internal impedance. The stability has been checked for those resistors.

    2) Backup time T can be calculated as following : I backup (~9uA)=C * (Vbackup-VMBLO)/T

    3)both caps can be charged. You need to make sure that the end of charge voltage, and the charge current are within the capacitor specification.

    most of the supercap have a higher cap but a lower voltage. charge cap have an higher voltage but a lower cap.

    If a long time constant is not necessary then cap can be selected because they are less expensive.

    Best regards,

    Flore