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TPS56339: Stability

Shinu.V.Mathew
Expert 7445 points
Part Number: TPS56339

Hi Team,

My customer is planning to use TPS56339 to charge 1F super cap in parallel with other connected loads and want to understand the device loop stability issues. Input V = 15V, Output V=5V. Can you please help with your inputs and comments. 

Regards, Shinu Mathew. 

  • 0
    TI__Expert 4795 points

    Hi Mathew,

    TPS56339 couldn't support this application becasue L&C has an range requirement to compliant with internal zero frequency.

  • 0 in reply to Vincent Zhang(BSR)
    TI__Expert 7445 points

    Hi Vincent,

    Thanks for the feedback.

    What device we can suggest for this application?

    Regards, Shinu Mathew. 

  • 0 in reply to Shinu.V.Mathew
    TI__Genius 14455 points

    Hi Shinu

       You can use WEBENCH to select devices that meet this Vin, Vout, Iout requirements. Start with a current mode converter and try changing the capacitance in the design to check if the design can work. I am investigating some more and will get back to you.

    regards,

    Gerold

  • 0
    TI__Mastermind 48180 points

     

    I think there may be some misunderstanding.

     response was based on an understanding that you were looking to have the super capacitor connected to the TPS56339's output directly.  As Vincent reports, that is not possible, since the L-C resonance frequency would be too low for the TPS56339's internal compensation to adapt to, but if there is a charging circuit limiting the current into Super Capacitor and also preventing it's high-frequency, low voltage back-feeding of the TPS56339's output, it might be possible.

    In addition to stability issues, the 1F super capacitor would also present a current limit / soft-start timing issue for any 5V converter.  Charging a 1F capacitor to 5V requires the delivery of 5C of charge, at 3A current, it would take almost 2 seconds for the output voltage to ramp from 0V to 5V, since the TPS56339 does not have a programmable soft-start time, the under-voltage protection will trigger when the 5-ms soft-start completes.  That would mean the "other connected loads" would also take upto 2-seconds to power up.

    However, if you have a super-capacitor charging circuit that is limiting the charging current and preventing the normal pulse by pulse ripple voltage from drawing current from the super-capacitor, even a current limiting LDO or hot-swap controller, that would also separate the Super-capacitor's capacitance from the output of the TPS56339 so that the super capacitor and charging circuit present a constant-current load to the TPS56339 and not 1F of loading capacitance.

    If you can let us know how you are charging the super-capacitor, and what you are planning to do with the energy you store there, we might be able to help you with a solution.

  • 0 in reply to Peter James Miller
    TI__Expert 7445 points

    Thanks Peter.

    Thanks for the inputs and feedback. 

  • 0 in reply to Shinu.V.Mathew
    TI__Mastermind 48180 points

     

    If you can let me know what your intent is, and how you were planning to connect the TPS56339, the parallel loads, and the Supper Cap, we might be able to help you with your design.

    If you are concerned about discussing your application and use case in this public Engineer to Engineer format, you can send me your direct e-mail address in a private message to my by clicking on my name  

  • 0 in reply to Shinu.V.Mathew
    TI__Mastermind 48180 points

     

    I am going to close this thread.

    If you get feedback on how the customer is connecting the super-capacitor and the parallel loads together, you can add to this thread to re-open it, or post a new thread.