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TPS51200 Average Model Bode Plot

James Crow
Prodigy 180 points
Other Parts Discussed in Thread: TINA-TI

Using the average model I tried to run the AC analysis to get a representative bode plot, but got what looked like a dc response. I haven't done Bode Plots with TINA-TI yet. Do I need to connect a function generator in the feedback network? I have enclosed the design.VTT_Bode.TSC

  • 0
    TI__Mastermind 41310 points

    James,

    Please take a look at the Average Reference Design for the device. I believe that you will find that you are missing the AC injection circuit for the Bode Plot. I am not quite sure what your circuit is using for an input/output for the bode characteristic. There are also notes in the reference design about what signals are being used.

  • 0 in reply to Britt Brooks - Online Design Tools
    Prodigy 180 points
    Britt, thank you for replying. In the datasheet section 8 figure 20 shows a typical DDR3 configuration, which is nearly the same as my design. Furthermore figure 21 shows the bode plot of that design, shouldn't I expect nearly the same results?
  • 0 in reply to James Crow
    TI__Mastermind 41310 points

    James,

    The reason I want you to look at the example is to see how to use the average model properly. You do not use an average model by simply dropping it into a schematic and running an AC analysis. You will notice a 10H and 10F capacitor used with the AC injection circuit to "break the loop" so that the Open loop characteristics can be seen. You will also notice that the enable does not need a time based enable function since you are simulating an AC simulation. It will need to be a DC source. You will also notice that the output is VO and the injection input is VOSNS. This will give you the Bode Plot from the AC simulation. In this case the output is set using an open circuit symbol. You could also use a voltage pin.

    Since you had mentioned that you had not run a Bode Plot before in TINA-TI, I as hoping that you could look at the example to see the proper way to set up the Bode Plot simulation.

    The reference design is also almost identical to the circuit in Figure 20, other than the capacitors have parasitic resistances and inductances shown. The initial values are also set for REFOUT and VTT (VO). The plot in TINA-TI starts at -180 instead of 0 as the datasheet shows.