TPS55340: charging large output caps

Part Number: TPS55340

Tool/software:

Hi there,

my application needs a 20V from a single Lipo Cell (3,1 to 4,2V). I want to power a sensitive analogue circuit that requires a noise "free" environment. Since I am using just pulses from the 20V, I plan to charge a 1000µF Cap with the Step up and then use the stored energy with the DCDC disabled. Since it will be repeated rapidly, I need to know how the TPS55340 will behave during the sort charging phases. (How can I controlled limit the drawn current / max duty of PWM or so to get a stable system with lets say max 5A input current or 400mA of output (even when the 1000µF is at a far lower voltage than 20V).

I am afraid, that the TPS55340 will run at its max PWM duty and run in its OCP during the charging phase...

I am locking forward to get suggestions :-)

  • Hi Tristan,

    When the output voltage is lower than 20V for a long time, the controller will enter peak current limit and frequency foldback.

    Please refer to 7.3.3 Overcurrent Protection and Frequency Foldback in the datasheet.

    Please set the soft start time as long as possible if you don't want to operate with peak current.

    Best Regards,

    Feng

  • Hi Feng,

    thanks for the reply! I read through the mentioned chapter and still have a question: Is there a way to use this IC to charge my large capacitor bank within the normal setup (no frequency fold back) and some controlled max current? Because I am afraid that I will lose efficiency when I run the IC at its max. current and the inductor at 1/4 of the designed frequency.

    I could think of a voltage limitation on the feedback pin to not go under 0.95V or so...?

    I just read again, and think the SS (oft-start) may be even better suited for that purpose. Furthermore, I just need to know what voltage at the SS pin leads to what max PWM and can just limit the SS voltage to not go above this value. Since I NEVER have a load at the IC, (I need to power some noise sensitive analogue circuit with it) I always charge capacitors with a too low voltage to the desired voltage, then go back to sleep (EN pin) and do my measurement. This cycle repeats every few ms. This is also a reason why I am not using the SS pin as designed, to not lose too much time within the startup procedure.

    Thanks for your help!

    Best regards

    Tristan

  • Hello Tristan,

    I wonder if the TPS55340 is the right part for this application. To me it looks as if you want to use a similar setup as shown in this app note: Supercapacitor backup power supply with TPS63802

    If this is the case, check the buck-boost converters or controllers which seem to fit better to your application than just a pure boost converter:

    AC/DC & DC/DC converters (integrated FET) product selection | TI.com

    AC/DC & DC/DC converters (integrated FET) product selection | TI.com

    Best regards,
    Brigitte