There are 2 TM PFC control IC’s, a primary and secondary. Each one has internal comparators and reference voltages which are independent of the other. When COMP is connected between the two pins, both 20-mV COMP-Discharge comparators must be satisfied before each load on COMP will be released.

There are several important highlights to note from Figure 4-3. By connecting VSENSE to VREF with a diode, the feedback of the secondary controller is disabled. Also, because both the primary and secondary controllers share a common COMP pin, they will have the same constant on time. The two UCC28064s will have their own zero cross detection (ZCD) and other protections such as 1st OVP, 2nd OVP, OCP and OTP can be set individually.