We are designing the PCM1789 Stereo Audio DAC into a new product.
The application data recommends using a second order Butterworth low pass filter at the output of the DAC in order to reduce out of band energy left over from the delta sigma modulation. Recommended AC and DC coupled circuits are found on page 33 of the data sheet. The topology of the multi-feedback Butterworth filter is a little unusual and not supported by standard filter design software including the filter design application from TI. We need to make a couple tweaks to the filter and could use some help.
We need the AC coupled version of the differential to single ended LPF. The example AC coupled circuit has a gain of 0.747. In our case we need a gain of 0.887.
We also prefer to use an MC33078 op amp rather than the OPA2134 used in the design example. We use the MC33078 in a number of other places in the product and would prefer to use it here as well. It is a good performing low noise high speed amplifier with decent GBP.
Could someone from TI provide a filter design for the PCM1789 based on the MC33078 and with a target gain of 0.887?
Alternatively, is there a recommended methodology for component value selection for a MFB 2nd order Butterworth topology?
