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UCC28710: Tina Ti Simulation - Startup Issue

Part Number: UCC28710

Hello All,

I'm working on a multiple output offline flyback converter using UCC28710, for the following specifications : 

- Output 1 : 16 V / 50mA

- Output 2 : 16V / 50mA

- Output 3 : 15V / 1A

Using the following transformer spice model : 

.subckt FLBTR_VF 6 3 2 1 7 8 9 10 11 12

Llp 6 3x 10u
Rp 3x 3xx 540m
Lp 3xx 3 450u

Ls1 7 8x 15.43u
Rs1 8x 8 1

Ls2 9 10x 15.43u
Rs2 10x 10 1

Ls3 11 12x 12.5u
Rs3 12x 11 0.031

Laux 2 1x 18.66u
Raux 1x 1 120m

K Lp Ls1 Ls2 Ls3 Laux 0.99


It appears that the controller does not start-up, as the current through the HV pin is zero.

Please find attached the simulation file. I would appreciate any remarks/advice that you may provide.

Thank you and best regards,


  • Hello,

    I would check your design using Webench first.  Even though it designs for a single output you can to the design as follows.

    1. Single output with total output output power this will give you the input capacitance and primary magnetizing current for the transformer.

    2. Do a design for each output.  This will give you the Np:Ns1:Ns2:Ns3 turns ratios as well the output power stage electronic components.

    Next go to the TI simulation model and run the simulation for the signal output to make sure it works.  You will be just adjusting the transformers turns ratio and magnetizing current at this time.  Once you have this model running then trying adding a second output and debugging it in Tina.  Finally when you get that output working you can go add the third winding and third output.

    If in your simulation you are not getting convergence issues and the output still is not coming up then it may be something wrong with how you are implementing your application.  

    The following link will bring you to an application note on how primary fault sensing works and the common issues with this technique and how to resolve them.  I believe this information will help you trouble shoot your design and you will find it useful.