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TINA/Spice/TPS61178: Problems with using Model with SiMetrix

Rex Huang
Prodigy 20 points
Part Number: TPS61178
Other Parts Discussed in Thread: TINA-TI,

Tool/software: TINA-TI or Spice Models

I have been using the Pspice model of the TPS61178 under SiMetrix environment..

I've observed that changing the resistor to set the switching frequency of the boost converter (at the FREQ/SYNC pin) does not change the frequency.

Is there an explanation to this or is this simply the model being incompatible to SiMetrix.

Would like to get some assistance as we want to run this under SiMetrix environment.

Thanks!

  • 0
    TI__Intellectual 2405 points
    Hi Rex,

    I simulated the TPS61178 model in PSPICE with published Startup testbench for different values of RFREQ resistor and observed that, the frequency before startup, remains constant at 500kHz, and gets updated based on RFREQ value during startup and in steady state. Did you measure the frequency in steady state? The model follows curve from figure 20 (Switching Frequency vs Setting Resistor) from datasheet.

    Please check the measurements again and if you still have issue, please upload the Simetrix schematic here for further debug and support.

    Thanks!!

    Best Regards,
    Mahavir Jain.
  • 0 in reply to Mahavir Jain
    Prodigy 20 points

    Hi Mahavir,

    Thanks for your reply.

    We do observe a fixed frequency of 500KHz during start up. 

    When there is an output load and the boost converter starts regulation, we can see that the switching frequency is at 1.2MHz (this is what we set via the resistor).

    However once steady stated, the frequency gets halved down to 600KHz. The load is roughly 10W.

    Are we missing something here?

    Regards,

    Rex Huang

  • 0 in reply to Rex Huang
    TI__Prodigy 60 points

    Hi Rex,

    Could you let me know the input output condition (the following details) of your experiment?

    vin,  vout, iout, RT resistor value? It will help me to debug why the frequency is halved down.

    Thanks,

    Akash

  • 0 in reply to Rex Huang
    TI__Prodigy 60 points

    Hi Rex,


    I simulated 10W load condition in the pspice model. (Vin=7.2V, Vout = 10V, Iout = 1A, RT = 145k ohm for 1.2 MHz frequency ).
    There are total 3 stages of complete startup:
    1. Precharge: In precharge, vout remains at vin*1.1 and device operated with constant 500 kHz frequency.
    2. Soft-Start: Vout is ramped from vin*1.1 to desired vout. This region operated with RT frequency.
    3. Steady State: once the vout is in steady state, device continues to operate with RT frequency. In my experiment, frequency did not half down in the steady state. It worked with 1.2MHz

    PFA the results for your better understanding.

    Thanks,
    Akashresults.pdf