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Help select a suitable LDO to charge the super caps?

Helen chen
Mastermind 40080 points
Other Parts Discussed in Thread: TLV1117, TPS746

Dear Sir/Miss,

We need to charge a 30F/2.7V  super cap with 1A-2A CC current. Seems a LDO with output constant current funciton is a good choice.

The input voltage of LDO is 4.5V maximum and 3.5V minimum.  Its output voltage is 2.7V with 1-2A CC current ability. Do you have a LDO which can meet this requirement?

  • 0
    TI__Guru 50190 points

    HI Helen,

    LDO's are fundamentally designed to regulate VOUT with the current and thermal limits as self protection mechanisms. That being said, your question does come up a lot. I took the liberty to simulate this idea and it may work. Simulation wise it seems OK, but the simulation does not consider the thermal behavior,

    With the following results

    Let me know if this helps.

    Regards,

  • 0 in reply to JCHK
    TI__Mastermind 40080 points

    Hi John,

    Thanks for your kindly help on this case. Your answer is really good, it is so detail. :)

    How about use TLV1117LV25DCYR or  TLV757 ? ( a short on LDO is expected during initial charging , as super cap is a transient short )

  • 0 in reply to Helen chen
    TI__Guru 50190 points

    HI Helen,

    Unfortunately, to work, this scheme will require a feedback pin. So the TLV757 and TLV1117 will not work. For a low cost 1A part with a feedback pin, the TPS746 could work. The sense resistor and feedback network would have to change to keep the current less than 1A. Again this should be built and tested to ensure that there are no thermal issues.

    I hope this helps.

    Regards,

  • 0 in reply to JCHK
    TI__Mastermind 40080 points

    Hi John,

    Thanks for your detailed and professional answer, its really helpful, thanks!