Figure 8-13 Simplified Equivalent Feedback Compensation Network

A typical compensation circuit could be type II (R_C and C_C) to have a phase margin between 60° and 90°, or type III (R_C, C_C, and C_ff) to improve the converter transient response. C_Roll adds a high-frequency pole to attenuate high-frequency noise when needed. C_Roll should be set to at least twice the crossover frequency to avoid interacting with the feedback compensation. It may also prevent noise coupling from other rails if there is possibility of cross coupling in between rails when layout is very compact.

Table 8-3 shows the recommended values for the compensation network components as an initial start. These result in the compensating zero of the Type II to match the dominant pole of the converter.

Table 8-3 Compensation Calculation Table

	TYPE II	TYPE III
Select cross over frequency to be less than 1/5 of switching frequency (typical is 1/10)
Set RC
Set CC
Add CRoll if needed to remove large signal coupling to high impedance COMP node.
Cff compensating capacitor for type III compensation network. Choose ƒzff same as FC.	N/A