UCC28C53-Q1: Pspice simulation not working

Abhijith Kannan

Part Number: UCC28C53-Q1
Other Parts Discussed in Thread: UCC28C43, UCC28C53

I design a PSR flyback converter for converting 50-85V DC to 12V DC using TI Webench Power Designer. Since I am new to designing power converters, I don't know whether the generated values for the components are correct or not. So I decided to do a pspice simulation using Pspice for TI. When I run the simulation, at first the it wasn't able to to get enough VDD so I decreased the HV startup resistance to 13k. I ran the simulation again and it turn ON this time. I was able to get VREF. But the output from the OUT pin isn't able to drive the mosfet. The output from the OUT pin reaches a max 1.9V and soon after it reaches 0. Also after sometime the VDD goes below to 7.6V which turns off the chip due to UVLO. The turn on again when the VDD goes above 7.6V and after sometime it falls and this keep on repeating. I have attached the design generated by webench and the pspice below for your reference.

The image given above result from the simulation.

Red - VDD

Pink - OUT

Yellow - FB

Green - Output of the flyback converter

over 2 years ago

0 Hong Huang over 2 years ago

TI__Guru 73785 points

Hi,

Please please provide your schematics for review.

0 Abhijith Kannan over 2 years ago in reply to Hong Huang

Prodigy 70 points

Sorry for the delayed response. Here's the schematic generated by Webench.

7418.WBDesign14.pdf

0 Abhijith Kannan over 2 years ago in reply to Hong Huang

Prodigy 70 points

Update I made a mistake while reading the graph from pspice. The output from the RT pin and OUT pin where pink in color. So the sawtooth like waveform is the signal from RT pin not the OUT pin. I actual output from the OUT pin reaches a max 1.9V when the device turns ON and after a few microseconds reaches to 0. I have the updated the question with the new image for info.

0 Hong Huang over 2 years ago in reply to Abhijith Kannan

TI__Guru 73785 points

Hi,

Please provide your updated schematics.

0 Abhijith Kannan over 2 years ago in reply to Hong Huang

Prodigy 70 points

3660.schematics.pdf

0 Hong Huang over 2 years ago in reply to Abhijith Kannan

TI__Guru 73785 points

Hi,

I suggest to simulate with a fixed supply to VDD (12V or so), so temporarily remove R17 and R16 associated circuit.

Also, PSpice for TI accept maximum 3 probes at time - but your circuit shows much more than 3 probes. Please use up to 3 probes each simulation time.

0 Hong Huang over 2 years ago in reply to Hong Huang

TI__Guru 73785 points

Hi,

Please follow my suggestions and do the debugging.

Also simple rejection does not help anything.

0 Abhijith Kannan over 2 years ago in reply to Hong Huang

Prodigy 70 points

As suggested I gave a fixed supply for VDD and disconnected the R17 and R16 associated circuit. I have attached the updated schematic and the results obtained.

Updated schmatics 2.pdf

Here Red is VDD, yellow is RTCT and pink is OUT. As you can see still not output from OUT pin.

+1 Hong Huang over 2 years ago in reply to Abhijith Kannan

TI__Guru 73785 points

Hi,

I suspect the MOSFET model has something wrong or needed to adjust.

I suggest you start with the below model - I have tried and it works. It is with UCC28C43, you can replace UCC28C43 with UCC28C53. Also I have tried and it works.

https://www.ti.com/lit/zip/slum033

After you have the above model with UCC28C53, then you can modify the above circuit to yours. This way can help you to start with a tested circuit so you would know at what point with your changes the model shows the issue then we can fix that instead of debugging your current circuit.

By the way, is UCC28C53 model in your circuit from TI? Just in case, you can replace UCC28C43 with UCC28C53 right in PSpice for TI of its library..

0 Abhijith Kannan over 1 year ago in reply to Hong Huang

Prodigy 70 points

As suggest I replaced UCC28C43 with UCC28C53 and I was able to get the same result as with UCC28C43. Now I'll update the circuit to the one that I got from Webench and see if it is working

0 Hong Huang over 1 year ago in reply to Abhijith Kannan

TI__Guru 73785 points

Hi,

No communication for a long time. I assume the issues are resolved. I will close this thread. If you need further support, you can re-open this thread of create a new thread.

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UCC28C53-Q1: Pspice simulation not working