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PSPICE-FOR-TI: Simulation of output current setting not working for TPS92518

Brian McKee
Intellectual 405 points
Part Number: PSPICE-FOR-TI
Other Parts Discussed in Thread: TPS92518HV, TPS92518

I'm running a simulation of my product in PSPICE-FOR-TI to determine efficiency.

My design uses a TPS92518HV.

You have helped me with a previous issue where the simulation wouldn't run, but I have a new problem.

I have a voltage source on the VIADJ pins to control the output current of the converter, but it is not working. The simulation always shows maximum current output no matter what I set it to. Even if I tie it to ground, the output goes to the maximum for the sense resistor I have chosen.

Could someone explain to me what I'm doing wrong, or advise me on how to fix the schematic?

Thank you very much.

  • 0
    TI__Intellectual 1675 points

    Hi,

    Our team has been looking into this issue. I have assigned this E2E thread to our team's expert, but please give us some time to look into it.

    Best Regards,

    Caroline

  • 0
    TI__Prodigy 130 points

    Hi Brian,

    Which VIADJ are you changing. The device has two channels and when I change the channel1 VIADJ, I can see that the channel1 current is changing. Please keep in mind that the input to the VIADJ should be an integer number between 0 and 255. When I changed the DAC values of VIADJ1, the current through D13 has changed. Below picture shows the waveforms in both channels.

    Regards

    Vahid

  • 0 in reply to Vahid Yousefzadeh
    Intellectual 405 points

    How do I connect the VIADJ1 pin on the symbol to a constant integer? I'm used to connecting wires with voltage or digital busses.

  • 0 in reply to Vahid Yousefzadeh
    Intellectual 405 points

    Also, do I drive voltage onto the Enable pins? Because they don't appear to be working either. Am I supposed to drive a 1 or 0 onto the Enable pins?

  • 0 in reply to Brian McKee
    TI__Prodigy 130 points

    Hi Brian,

    What I meant, is that you would program the constant DC source already connected to the VIADJ pins with an integer number between 0 and 255. For example in picture below that is what I did, and I was able to change the current in D13.

    Regards

    Vahid

  • 0 in reply to Brian McKee
    TI__Prodigy 130 points

    Hi Brian,

    The EN pin, may have internally been set high. The model intends to show the basic functionality.

    Also, on a separate note, I saw in your previous messages, you are trying to perform efficiency calculation using this model. I just wanted to emphasize that this model will not give you an accurate data for efficiency. The model is only intended for basic functionality. Non of the parasitic are modeled, gate drive loss is not modeled, an ideal switch and diode are used for external FET and diode, inductor core loss is not modeled, etc.

    For efficiency, I suggest you get an EVM and test the EVM to obtain a baseline for your efficiency.

    Regards

    Vahid

  • 0 in reply to Vahid Yousefzadeh
    Intellectual 405 points

    Thanks Vahid.

    I didn't mean the EN pin, I meant the PWM pins, sorry I got confused.

    Do the PWM pins work with voltage from 0 to 3.3. I have a pulse generator connected to PWM2 and the output changes, but when the current shuts off, the voltage actually goes up, which makes no sense.

    Also, I copied your circuit and set the voltage into the IADJ2 pin to various numbers and the circuit is still generating full current.

    How come the voltages listed on your DC supplies don't match the voltage on the IADJ pins? Mine do (after running a sim), and it doesn't work.

  • 0 in reply to Brian McKee
    TI__Prodigy 130 points

    Hi Brian,

    Lets solve one issue at a time. Could you send me picture and the waveforms of what you change on IADJ and what LED current you get on a particular channel. I do not have any problem on my simulation setup to change the LED current.

    Thanks

    Vahid

  • 0 in reply to Vahid Yousefzadeh
    Intellectual 405 points

    My TI Spice schematic

    Here is a snip of my schematic. Thanks for your help.

  • 0 in reply to Brian McKee
    TI__Prodigy 130 points

    Hi Brian,

    It seems that you have changed the original TI PSPICE file of TPS92518. I recommend that you first see if you have the same issues above with the original design and then start modifying the design to match your circuit. 

    Also, TPS92518 has a NFET driver. You have added a PFET in your design.

    If the issues above still remains for the original TI design, please send me the waveforms of the LED current and switch node voltage.

    Thanks

    Vahid