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TPS54A20: TPS54A20 Design issues

J
Expert 1065 points
Part Number: TPS54A20

Tool/software:

We are considering using TI's TPS54A20 to implement a series capacitor buck converter and have a few questions for TI experts:

  1. When selecting switches for a series capacitor buck converter, is SiC or GaN generally preferred, and what are the reasons for this choice?
  2. In the architecture of a series capacitor buck converter, is more emphasis placed on minimizing switching loss or conduction loss?
  3. What is the typical switching frequency range for a series capacitor buck converter, and what are the reasons for this range?
  • 0
    TI__Expert 5318 points

    Hi J,

    1. GaN switches tend to have lower gate charge, therefore good for high frequency(HF) apps. SiC on the other hand are great for high voltage apps.

    2. It's typically more on minimizing switching loss as they tend to operate at HF. Conduction loss is important still, specially at low output apps.

    3. On average, somewhere between 500kHz to MHz. With HF you can use smaller inductor and caps, with LF you can reduce switching loss and therefore better efficiency.

    TPS54A20 has a HF range, above typical bucks, ranging from 4-10MHz. In addition, TPS54A20 uses Constant on-time (COT) control mode, which essentially keeps the on-time fixed, allowing the control loop to quickly adjust switching based on VOUT changes and also maintains good efficiency at light loads.

    Regards,

    Eileen

  • 0 in reply to Eileen Hernandez Hernandez
    Expert 1065 points

    Hi Eileen,

    Thanks for your answer.

    1. I would like to know which one is suitable for Series capacitor buck topology, Sic or GaN device?
     As you said, Series capacitor buck is typically operating at HF, so GaN device is a good choice?

    2. Does this architecture have ZVS functionality?

  • 0 in reply to J
    TI__Expert 5318 points

    Hi J,

    Unfortunately I don't support neither of those modes. I support TPS54A20 device. Here is an app note that goes into detail on what you are looking for: https://www.ti.com/lit/an/slyt801/slyt801.pdf 

    Regards,

    Eileen