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TPS536C5: Output Impedance in COT Control

RYO KASAI
Prodigy 10 points
Part Number: TPS536C5

Tool/software:

Hello, I would like to measure and simulate the output impedance of your COT controlled power supply, so I would like to know more about it.
The output impedance is shown on page 24 of the document linked below, but how is this measured or simulated?
For my understanding, it's difficult to reproduce the sudden current load change in COT control with AC analysis, so are you doing any unusual measurements or simulations?

https://www.ti.com/content/dam/videos/external-videos/en-us/7/3816841626001/6202317324001.mp4/subassets/session3_jp-voltage_regulator_design_and_optimization_for_high-current_fast-slew-rate_load_transients_0.pdf

  • 0
    TI__Intellectual 1100 points

    Hi Ryo, 

    The slide shown looks like a Simplis simulation, from my understanding to get a full output impedance plot the simulation for a real board would be a combination of a PDN extraction alongside the controller model. 

    Thanks, 

    Ryan

  • 0 in reply to Ryan Blake
    Prodigy 10 points

    Thank you so much for the answer. I am wondering if the AC analysis can represent the response of the power supply during a sudden change in current load when graphing the output impedance of a COT power supply. I would like to know if there is some special simulation method.

  • +1 in reply to RYO KASAI
    TI__Intellectual 1100 points

    Hi Ryo,

    Simplis is capable of running transient/dynamic current analysis and frequency analysis like Bode or Output Impedance. For the most part, frequency and transient analysis represent the same information just in different contexts. A transient response is effectively an impulse with a range of frequencies which are represented in the output impedance plot. What we see in slide 24 is the output impedance for two different control topologies/simplis models where one has a higher effective max bandwidth due to the converter design. When the Zout goes above spec it implies a transient sweep would fail voltage margins as the controller is unable to keep the Zout/Overshoot/Undershoot under target at that frequency. The reverse is also true where if you pull a transient and the voltage is out of spec, it implies the Zout goes out spec at some frequency. 

    Thanks, 

    Ryan