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UCC28704: UCC28704 Tina TI simulations not working as expected.

Part Number: UCC28704


Hope you are doing good.

We are trying to run the simulation model of ucc28704 based on the webench provided report.

The output is falling to zero and the VDD pin is reading 100V which is way too high from the datasheet.

I am attaching the tina file and the webench report below


AUX_12V_rev1_1 - autosave 20-10-03 16_44 - autosave 21-01-06 17_12.TSC

Can you help us understand why is it behaving this way?

We are using the same board setup and the board is failing to give an output of 12V. it is stuck at 110mV.


Warm Regards

Harini Krishna 

  • Hello,

    Unfortunately I can't open the simulation file. Can you attach screenshots of your schematic used in the simulation?

  • Hi Pye,

    Hope you are well.

    I am sorry for the corrupt file.

    please find the attached image below for the simulations that we are running to validate the bench design.


    Warm Regards

    Harini Krishna

  • Hello,

    Doing a comparison of the component values of the schematic in the simulation to the values on the design, it looks like Rcs=1.5Ohms on the design while the corresponding component R4=1.5kOhms in the simulation. If the voltage on the CS pin is much higher than it should be, the device may be detecting a Primary Over-Current fault which can explain the lack of regulation.

    Try changing that component value and see if that fixes the issue.

  • AUX_12V_rev1_1 - autosave 20-10-03 16_44 - autosave 21-01-06 17_12 (1).TSCHi,

    We rectified the mistake. and tried running the simulation. but nothing really changed.

    Is there any simulation setting that needs to be set in order to run the proper simulations?

    We got this design from webench and made a prototype and found out that the prototype is failing.

    We would like to conform to the design using simulation before going for the next revision. 

    Attached the TINA TI model for the UCC28704 power supply design. Please simulate and confirm the working of it.


    Warm Regards

    Harini Krishna.

  • I don't have the program used to open the file, nor do I have the ability to download the program.

    Generally though, to confirm the operation of a simulation, there are a few things you can do. Try these debug steps in this order.

    • First, ensure the simulation is a transient simulation starting from 0Vin. You may have problems in a simulation where you directly apply the final Vin value at the start because the simulation will need to initialize the nets. If you want to see the steady state operation, you'll first need to simulate the startup.
    • Next, check whether or not the device is switching by probing the DRV signal. If the device is not switching, check the other inputs to the device to ensure they are in the proper range of operation and the device is not going into a fault state. If a pin has a value that looks to be outside the range, check that the components connecting to that pin are correct.
    • You may also want to try disconnecting VDD from where it connects to VS1 through the three 2.67Meg resistors, instead using a DC supply that transitions from 0-25Vdc. You mentioned earlier that the VDD was at 100V, and doing this may help simplify debug in checking where that high voltage is coming from.
    • Also, rather than using a Mosfet, it may help to model that component as a switch instead.

    As a side note, TI does provide a PSpice Transient model for this device that you can find on the product page in the "Design & development" section under "Design Tools and Simulation" that you may be able to use as a reference or edit to suit your needs. This can be run using PSpice for TI