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LM3402HV Simulation problems

Julian de la Rua
Prodigy 30 points
Other Parts Discussed in Thread: LM3402HV

Hi,

There seems to be a problem with the designer/simulation using the 3402HV Chip. Using webbench I designed for an LED string to run at 150mA. Vf is 3.2 at 150mA, 5 of them in series for a 16V output. The figure below shows the simulation for the design that was suggested by webbench (with nothing modified by me). The right Vo for this design should be around 16.2V (16 from LED's + .2 from Rsns) instead its shifted higher. The Current If should be centered at 150mA which it isn't and it's outputting a higher Irms.

Another problem with the webbench interface is inputing a desired frequency. Given my condition my maximum frequency allowed is 912KHz which is correct in the image below but if you try to input a value in the allowed range it doesn't let you, instead it tells you the value has to be lower than 866.5Khz but even if you use a value lower than that you still get the same error and are not allowed to input any values

Thank you!

-Julian

  • 0
    Prodigy 30 points

    To add some more information. The input voltage is 59.2 V. The LED string is made of five 3.2V/150mA LED's. The operating frequency desired is 909KHZ (133K Ron).

  • 0
    TI__Intellectual 1825 points

    Hello Julian,

    Thank you for your interest in Texas Instruments' power management units and for bringing these issues to our attention.  I apologize for any problems you ran into using WEBENCH® for your LM3402HV design.

    I am currently looking into possible causes for these issues. I will get back to you as soon as I can with what I find.

    If you have any other questions, comments, or concerns, please let me know.

    Regards,
    Jonathan Arzadon
    Applications Engineer
    WEBENCH Design Center
    Texas Instruments

     

  • 0 in reply to Jonathan Arzadon
    Prodigy 30 points

    Hi Jonathan,

    Did you ever get to take a look?

    Thanks,

    -Julian

  • 0 in reply to Julian de la Rua
    TI__Intellectual 1825 points

    Hello Julian,

    Sorry for the delay in my response.  My colleagues and I did get a chance to look into these issues.  Here is what we found:

    1)  In regards to the frequency issue, we weren't able to duplicate the error where you are unable to enter in a specified value.  We will keep an eye out for other instances of this issue to try and pinpoint the cause of it.

    2)    Looking at your waveforms, it doesn't look like the values are that far off from the expected values.  Since our SPICE model is a behavioral model, we can't accurately model the device to match the calculated values, but it still provides a good representation of the circuit.  

    We did look into the issue, however, and  we discovered that the current goes above the expected/calculated value by a small amount due to some propagation delay in our SPICE model, which explains why there's a small increase in both the LED current and the output voltage.  

    I hope this helps you.  If you have any other questions, comments, or concerns, please let me know.

    Regards
    Jonathan Arzadon
    Applications Engineer
    WEBENCH® Design Center
    Texas Instruments