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I am using a Texas Instruments TAS5717 in a design. It is a 10W audio class-D amplifier.

For my design, I have copied the schematic from the evaluation board, shown on pg. 17 of this PDF. I used the values for the inductor and capacitors as shown, and things "work" on a prototype spin of my board. I would like to characterize and fine tune the circuit now. The current inductors are quite bit and my board size limited. I would like to know how switching to smaller inductors will impact the circuit.

Here is my schematic of the output filter:

output filter schematic

While looking for more material on this subject, I came across this TI document on class-D LC filter design. Inside, it explains the differences between "AD" and "BD" modulation. It also shows some nice plots of impedance vs. frequency and gain vs. frequency for selected components.

One of my issues is that the evaluation schematic does not match up exactly with the schematic shown in the LC filter design guide. (C7/C10 and R55/R56 are not present. What do they do? - Edit: I learned C7/R55 and C10/R56 are RC snubber circuits to aid in EMI suppression.)

I will be using this device in "BD" mode, unless there is a compelling reason to use "AD" mode. (ie C9 not placed).

I would like to be able to characterize the evaluation schematic filter and experiment with different parameters to see the effect, and create plots similar to those shown in the LC filter design guide. Is there a way to model this "BD" filter in PSPICE/LTSPICE?

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Ti has it's own SPICE tool much like LTSpice is for LT. It is called Tina and it might even have the macro models for your device.

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  • \$\begingroup\$ Sadly no models for my device. I'm looking for a more generic way to model a BTL amplifier, anyway. \$\endgroup\$ – dext0rb Jun 7 '13 at 5:27
  • \$\begingroup\$ but you can use the tool to model the network anyways. \$\endgroup\$ – placeholder Jun 7 '13 at 5:28
  • \$\begingroup\$ I am playing with TINA now, but I have never used it before so I am a little slow to getting this going. Going to use a different IC, but similar class-D BTL setup. I have the TPA31182D2 reference design loaded up, but I'm not sure how to make the graphs I want. I did a plot of Amplitude vs Frequency and it starts out at -154dB ??? \$\endgroup\$ – dext0rb Jun 7 '13 at 18:13

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