• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 3 answers
  • Subscribers 63 subscribers
  • Views 956 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM25116: SPICE Average Model does not Show the Same Result as Datasheet

Hao Jie Chan
Intellectual 320 points

Part Number: LM25116
Other Parts Discussed in Thread: PSPICE-FOR-TI,

Hi TI,

The model downloaded from the "Design Tools and Simulation tab" https://www.ti.com/lit/zip/snvm863, when imported into LTSPICE, and with the schematic modified to datasheet application design, gives a really different result. 

As shown are my LTSPICE schematic, and the schematic from datasheet:

My DC gain is only 2.45dB, which differs a lot to 17dB estimated. 

Is there anything to do to improve the model?

  • 0
    TI__Guru 68581 points

    Hello Hao 

    Unfortunately TI doesn't support LTSPICE. TI recommends customers to use PSPICE-FOR-TI. Please request and download PSPICE-FOR-TI at  https://www.ti.com/tool/PSPICE-FOR-TI 

    - Eric Lee (Applications Engineering) 

  • 0 in reply to EricLee
    Intellectual 320 points

    Hi Eric,

    I've duplicated the schematic in PSPICE:

    As you can see, the DC gain is way off.
    Some observations: I cannot change the Cout value... which makes it pretty useless since Cout is an important parameter.

    Also there is no way to change Rsense?

  • 0 in reply to Hao Jie Chan
    TI__Guru 68581 points

    Hello Hao 

    The gain at 100Hz is 44dB which is much higher than 2.45dB from LTSPICE simulation result, and 44dB is in normal range. 

    You can change COUT value by editing LM25116_AVE.LIB file manually. Please replace the netlist inside '.SUBCKT Cout 2 4' and '.ENDS' like this using Notepad. RESR is ESR resistance. COUT is output capacitance.  

    *$
    .SUBCKT Cout 2 4
    RESR 2 3 10E-3
    COUT 3 4 100E-6
    .ENDS
    *$

    -Eric Lee ( Applications Engineering) 

  • 0 in reply to EricLee
    Intellectual 320 points

    But if you refer to the datasheet plot, at 1kHz, it's <20dB, PSPICE returns 25dB, that's a huge difference.

    Also, where should I edit the file in PSPICE? The built in model is encryted. Should I replace it with the unencrypted one?
    And anyway, the DC gain should not be affected by Cout, am I understanding it correctly?

  • 0 in reply to Hao Jie Chan
    TI__Guru 68581 points

    Hello Hao 

    Please refer the overall loop response gain plot, not the modulator gain plot. There can be a difference between the simulation result and bench test result but it shouldn't be a lot. 

    Yes, please edit the unencrypted model , not the encrypted model.

    Yes, Ideally, DC gain (at frequency zero) is not affected by Cout. But, the gain at 1kHz can be affected by Cout if the load pole frequency is low. 

    - Eric Lee ( Application Engineering)