# AC Analysis of COT Control of Buck Converter

**URL:** <https://forum.plexim.com/t/ac-analysis-of-cot-control-of-buck-converter/1191>\
**Category:** PLECS\
**Tags:** analysis-tools, buck-converter, cot-control\
**Created:** [December 13, 2022, 12:22pm UTC](https://forum.plexim.com/t/ac-analysis-of-cot-control-of-buck-converter/1191 "2022-12-13T12:22:08Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![luizgsmartins](https://avatars.discourse-cdn.com/v4/letter/l/45deac/32.png) [@luizgsmartins](https://forum.plexim.com/u/luizgsmartins)\
**Post date:** [December 13, 2022, 12:22pm UTC](https://forum.plexim.com/t/ac-analysis-of-cot-control-of-buck-converter/1191/1 "2022-12-13T12:22:08Z")

</div>

Hi,I would like to learn how to obtain the Control-to-Output Frequency Response of a Contant On-Time (COT) Control of a Buck Converter using the Multitone Analysis tool. The parameters of the Converter are as follows:

L = 300e-9 HC = 56e-6 F/560DCR = 0 OhmESR = 6e-3 OhmR = 120e-3 OhmTon = 0.33e-6 sFsw = 300e3 Hz;The COT Controller was implemented using FSM. I’ve applied a perturbation signal to the reference input (Vref) and measured the reponse. Then using the Multitone Analysis Tool, used the following parameters

Initial simulation period: 1e-4 (s)Frequency range: [1e3 150e3]Amplitude: 1e-3Perturbation: vref’Response: vo’The image below ilustrates the schematic of the regulator.

 ![361](https://europe1.discourse-cdn.com/flex006/uploads/plecs/original/1X/97b57d0e867182eb3f33fe384374f7c78b2443ba.jpeg)

The image below ilustrates the implementation of the COT Control using FSM.

 ![361](https://europe1.discourse-cdn.com/flex006/uploads/plecs/original/1X/98a7c57c24534aa403d15fb8396cf20db4475c79.jpeg)

The ideia is to get the Control-to-Output Transfer Function according to what was obtained in the following paper “New Modeling Approach and Equivalent Circuit Representation for Current-Mode Control”, by Jian Li and Fred. C. Lee.

 ![361](https://europe1.discourse-cdn.com/flex006/uploads/plecs/original/1X/c33cc13a69e9d169a49a647bf0d29c1329b45531.jpeg)

When I try to obtain the same results using the Multitone Analysis, this is what I get.

 ![361](https://europe1.discourse-cdn.com/flex006/uploads/plecs/original/1X/cab22e93c028113aca8bb52065c53c0b32912bca.jpeg)

Thanks in advance.

[COT\_AC\_Analysis\_Forum\_PLECS.plecs](https://forum.plexim.com/uploads/short-url/uH5AlSCdveV4M2MEagFvWgU6Us4.plecs) (23.8 KB)

---

<div class="post-metadata">

**Author:** ![Kris\_Eberle](https://dub1.discourse-cdn.com/flex006/user_avatar/forum.plexim.com/kris_eberle/32/6_2.png) [@Kris\_Eberle](https://forum.plexim.com/u/Kris_Eberle)\
**Post date:** [December 15, 2022, 2:29pm UTC](https://forum.plexim.com/t/ac-analysis-of-cot-control-of-buck-converter/1191/2 "2022-12-15T14:29:07Z")

</div>

I see that the plots have a similar behavior as the ones from the paper (we can probably help you to get a “cleaner” Bode plot result), but is your main question the gain magnitude? Are you sure you are comparing the circuit parameters exactly to the model proposed in the paper?