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TPS62110 driving a super capacitor

David Seymour
Prodigy 50 points
Other Parts Discussed in Thread: TPS62110, TPS62750

I have a circuit with a TPS62110 driving a 350F super capacitor at 2.5V.  The datasheet talks about operation when an output voltage is present and the device is disabled.  Any issues/concerns with the device enabled and starting up with this kind of load when it has no charge or when charged? 

 

The input voltage can go away then come back at any time.  What is the leakage current when no input is present and the output (super cap) has a 2.5V charge on it?  Any concern about damaging the TPS62110?

 

With this kind of load what is the recommendation for an output capacitor?

 

-David

  • 0
    TI__Guru**** 150900 points

    You should definitely order the EVM and test it with this extreme setup.  You might add this circuit to increase the soft start time: http://www.ti.com/lit/an/slva307/slva307.pdf

    If Vin is removed, Vout will appear on Vin due to the high side MOSFET body diode.  If EN, the device will enter 100% mode.

    The above will increase the leakage current as now it flows through the body diode to all the circuits on Vin.  Other leakage currents are through the various pins on the circuit: low side FET, FB pin, etc.  These are specified.

    The TPS62750 was designed to drive huge caps, so it might also be of interest.

  • 0 in reply to Chris Glaser
    Prodigy 50 points

    From the TPS62110 datasheet it says regarding Soft Start:  "Therefore, the start-up time depends on the output capacitor and load current."  So in my case where my output capacitor is 350F will the soft-start automatically stay in play for a longer time constant since Cout is so large?

     

    Regarding input voltage dropping out while device is enabled and output is charged to 2.5V; Won't the Undervoltage Lockout circuit protect the device under these conditions or is it only valid down to 3.1V which is the Vina minimum voltage?  If that is the case using an external circuit to minitor the input voltage and disabling the part via EN line when the input voltage drops below 3.1V should provide proper protection and only subject the input load to the leakage currents specified, correct?

  • 0 in reply to David Seymour
    TI__Guru**** 150900 points

    Yes, the SS time will extend with a huge output cap.

    The UVLO just turns the part off when Vin is too low to prevent abnormal operation of internal circuits due to a low supply voltage.  I believe you refer to the output voltage bleeding back to the input.  This is through the body diode, which cannot be turned off being a diode.