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Original question:

TPS543C20A: A couple of general questions

TPS543C20A: Fixed frequency

Liu Yang
Expert 8775 points
Part Number: TPS543C20A

Hi Team,

TPS543C20AEVM-054 is called “40-A fixed frequency non-compensation stackable synchronous buck converters evaluation module”,
but can I change the switching frequency FSW from 500 kHz to 1 MHz by changing R14 (resistance of Frequency setting pin RT) from 40.2 kOhm to 19.1 kOhm?
According the data sheet of the TPS543C20A, I think it can works at FSW = 1MHz, but it is called "fixed frequency", so I asked you for confirmation.

Also, if there is any attention to changing FSW, please let me know.

Best Regards,
Tom Liu

  • 0
    TI__Genius 17905 points

    Hi Tom,

    Yes, the switching frequency can be changed by modifying the R14 resistor.

    The TPS543C20A is called a fixed frequency device because the switching frequency is oscillator-based (internal, but you can also synchronize to an external clock). Once the frequency is set, the switching frequency is very stable over line, load, transients, etc. This is with operation with API/BB feature disabled -- more on that later.

    On the other hand, there are devices that are instead based on constant on time (COT) control. These will have varying switching frequency when responding to load- or line-transient events, but will often have better transient response than a fixed frequency device.

    This white paper discusses in detail the fixed frequency advanced current mode control (ACM) control used in TPS543C20A.

    The TPS543C20A does have an optional API/BB feature which will allow it to improve its transient response, but the additional pulse injection of API means that the frequency is not truly fixed during transients. You can see Section 8.4.12 in the datasheet for more details on that.

    Regards,
    Kris