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TPS63020: Driving a supercapacitor (1F) load

Martin Clemons
Prodigy 80 points
Part Number: TPS63020

Hello,

I'm planning on using the TPS63020 converter to drive and intermediate supercapacitor buffer stage, with another step-up converter being supplied by supercap. See block diagram below:

-----------        ------------        ---------------        ---------------        ----------------------
| Battery | -----> | TPS63020 | -----> | 1F supercap | -----> | boost dc:dc | -----> | load 125mA nominal |
-----------        ------------        ---------------        ---------------        ----------------------
1.8-3.6V                                4.6V nominal                                  5.0V

The TPS63020 datasheet in section 10.2.2.2.2 clearly states: "There is also no upper limit for the output capacitance value."

I want to make sure that my configuration is not going to destabilize the TPS63020 control loop. The ESR of the supercap is ~40mΩ.

Thank you!

  • 0
    TI__Mastermind 20900 points
    Hello Martin,
    it is correct, that there is no upper limit of the output capacitance and the device should be able to start into a 1F cap. It might need to increase the soft start time (see www.ti.com/.../slva553.pdf).

    Could you explain why you use this staged converter design?

    regards,
    Julian
  • 0 in reply to Julian Hagedorn
    Prodigy 80 points

    Julian,

    Excellent, thanks for your response. As far as using the staged converter design, my power supply specifications are:

    1. Provide a regulated +5.0V supply with sufficient current capacity for expected load
    2. Input voltage may be between 0-3.6V depending on supply battery chemistry and SOC. Minimum operating voltage is 1.8V.
    3. Provide a 1F supercapcitor backup to +5V supply. Backup must transition seamlessly (without voltage glitch on +5V line) when input voltage is temporarily interrupted.
    4. The supply battery as well as the supercapacitor have very low ESR (40mΩ), so a controlled method for charging the supercapacitor is required.

    I felt like the staged design fulfills the specifications simply, as well as utilizes a significant portion of the supercap's voltage range and thus maximizes the energy available from the supercap. If there's a better approach that you're aware of I'm certainly open to suggestions!