TINA/Spice/LM5175: Determining transfer function for power supply

Rohit Baranwal

Part Number: LM5175
Other Parts Discussed in Thread: TINA-TI, ,

Tool/software: TINA-TI or Spice Models

Hi, I am evaluating the LM5175 DC/DC controller. I intend to build a 8-36V input, 15V, 4A output power supply for an operating temperature of 85C. I designed the controller using bode analysis and am trying to simulate the TINA -TI model I downloaded using webench. The model simulates fine, as in I Can see the voltage and current at different points in the circuit and I can run it at rated load. But I want to view the frequency response of the system (output voltage to disturbance). I have inserted a supply VG2 between the feedback resistor and the output voltage rail. When I try to get the bode plot, the software throws up an error saying that it cannot find the operating point. I am wondering if this is due to LM5175 not starting right at the beginning (startup time) and therefore, the analysis is not completed. Anyway, I need help to figure out how to view the frequency response of the system. The TINA-TI simulation has been attached with this post for anyone who wishes to view that.LM5175_sim_up_tf_analysis.TSC

over 8 years ago

0 Britt Brooks - Online Design Tools over 8 years ago

TI__Mastermind 41310 points

Rohit,

The TINA-TI model exported is a transient model and can only be used for time dependent simulations. The AC response simulation in TINA-TI would require an AC model (Average model) which we do not currently have available. You can look at the frequency response in WEBENCH under the charts button. The Bode Plot is one of the charts available. Bode Plot simulation is not enabled for the device.

0 Rohit Baranwal over 8 years ago in reply to Britt Brooks - Online Design Tools

Expert 1025 points

Hi Britt, thanks for the reply. I understand that I can see bode plots in Webench, but Webench picks the components by itself and uses that circuit to generate bode plot. I made a design that webench cannot seem to pick and therefore I cannot use Webench to generate bode plot. Any suggestions? Is it possible to modify components in Webench to choose your own design and then generate bode plots?

0 Nikhil Gupta (Product Folder Models) over 8 years ago in reply to Rohit Baranwal

TI__Mastermind 39210 points

Rohit,

Consider using this as well: www.ti.com/.../lm5175quickstart-calc
It has a Bode Plot function for this device.

0 Rohit Baranwal over 8 years ago in reply to Nikhil Gupta (Product Folder Models)

Expert 1025 points

Hi Nikhil, I have used this tool as well. Based on this tool, my design should work just fine for the conditions that I have designed it for. However, the converter only works in the boost range (Vin = 8-14) and then fails to generate voltage in the buck or buck boost range (Vin=15-36). I can share the design if you can help me figure out if there is a problem with the values chosen. I can also share the pcb layout if that that helps.

0 Vijay86929 over 8 years ago in reply to Rohit Baranwal

TI__Genius 11490 points

Hi Rohit,

Since this is no longer a Spice/bode plot problem it will be good to generate another thread describing in some detail the behavior of the converter when it does not work.

We have some material on LM5175-Q1 site on PCB design. Please also see the following blogs series:

https://e2e.ti.com/blogs_/b/powerhouse/archive/2017/02/23/four-switch-buck-boost-layout-tip-no-2-optimizing-hot-loops-in-the-power-stage

Thanks and regards,
Vijay

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TINA/Spice/LM5175: Determining transfer function for power supply