The UCD3138x filter is a PID filter with many enhancements for power supply control. Some of its features include:

• Traditional PID Architecture
• Programmable non-linear limits for automated modification of filter coefficients based on received EADC error
• Multiple coefficient sets fully configurable by firmware
• Full 24-bit precision throughout filter calculations
• Programmable clamps on integrator branch and filter output
• Ability to load values into internal filter registers while system is running
• Ability to stall calculations on any of the individual filter branches
• Ability to turn off calculations on any of the individual filter branches
• Duty cycle, resonant period, or phase shift generation based on filter output.
• Flux balancing
• Voltage feed forward

Here is the first section of the Filter :

Figure 9-10 First Section of the Filter

The filter input, Xn, generally comes from a front end. Then there are three branches, P, I. and D. Note that the D branch also has a pole, Kd Alpha. Clamps are provided both on the I branch and on the D alpha pole.

The filter also supports a nonlinear mode, where up to 7 different sets of coefficients can be selected depending on the magnitude of the error input Xn. This can be used to increase the filter gain for higher errors to improve transient response.

Here is the output section of the filter (S0.23 means that there is 1 sign bit, 0 integer bits and 23 fractional bits).:

Figure 9-11 Output Section of the Filter

This section combines the P, I, and D sections, and provides for saturation, scaling, and clamping.

There is a final section for the filter, which permits its output to be matched to the DPWM:

	Figure 9-12 Final Section for the Filter

This permits the filter output to be multiplied by a variety of correction factors to match the DPWM Period, to provide for Voltage Feed Forward, or for other purposes. After this, there is another clamp. For resonant mode, the filter can be used to generate both period and duty cycle.