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TM4C1294NCPDT PWM Output Impedance

Jacob Putz
Intellectual 665 points

Other Parts Discussed in Thread: TM4C1294NCPDT

Is the output impedance for the PWM block(s) known for TM4C1294NCPDT?  I am attempting to create a pSPICE simulation with a filter and want to see the effects of the output impendance @ 1MHz has on the filter.

  • 0
    TI__Guru**** 244450 points
    Hello Enforcer83,

    You can refer to the IBIS models on TM4C129NCPDT web page.

    http://www.ti.com/product/TM4C1294NCPDT/toolssoftware#simulationmodels

    Regards
    Amit
  • 0
    Intellectual 665 points

    What am I looking for?  I am not familiar with IBIS models.  I tried searching for keywords such as PWM and M0PWM0, since the file is so big, without success.

    When I searched for PF0, I got 2.37158E-01, 5.23178E-09 and 1.15936E-12 for R_pin, L_pin and C_pin and then R_Pkg, L_pkg and C_pkg set respectively to 2.48E-01, 5.35E-09 and 1.20E-12 nominally.  I don't know how to interpret the order of this information.  Is it set up as follows, in spice syntax?

    R_pin Vin  2     2.37158E-01
    R_pkg 3    4     2.48E-01
C_pin 3    0     1.15936E-12
C_pkg Vout 0     1.20E-12
L_pin 2    3     5.23178E-09
    L_pkg 4    Vout  5.35E-09

  • 0 in reply to Jacob Putz
    TI__Guru**** 244450 points
    Hello Enforcer83,

    The IBIS models serve as simulation models in place of Spice Models.

    The order of the information is Ohms, Henry and Farad. So in this case the E-xy will correspond as Ohms, nano Henry and pico-Farad.

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Guru 47900 points

    In defense of Amit's well detailed handling of his firm's IBIS models - may I state that in the past 8 years - using the PWM Generators w/in multiple ARM MCUs - (to effectively control BLDC Motors, large display backlights, and various power supplies) we've not found the need for such PWM-pin, output-stage detail.

    In each/every case we've imposed some form of PWM output buffer stage - as we avoid (like the plague) casting the MCU in the role of, "Beast of burden."  (we don't believe that's the best role for the MCU - and is far better served by "purpose designed" devices.  (i.e. various gate drivers,  FETs, etc.)

    Beware that Amit's (often) advised clients to be cautious in drawing too much current from any (single) side of the (4-sided) MCU.  Rear of the MCU manual details - yet the issue (may) be best avoided (as I've noted) via your use of, "more suitable" output devices!