AP64501

Document number: DS41980 Rev. 4 - 2

18 of 26

www.diodes.com

August 2019

© Diodes Incorporated

AP64501

Application Information (cont.)

16

External Loop Compensation Design (continued)

+

–

gm

VOUT

R1

R2

VREF

C4

R5

C5

C6

Error

Amplifier

+

–

+

RT

SE

PWM

Comparator

VSUM

FB

Figure 26. Type ll Compensator

Figure 26 shows a Type ll compensator. Its transfer function is expressed in the following equation:

(

) (

)

(

) (

)

Eq. 12

Where the poles and zeroes are:

Eq. 13

Eq. 14

Eq. 15

Eq. 16

The goal of loop compensation design is to achieve:



High DC Gain



Gain Margin less than -10dB



Phase Margin greater than 45°



Loop Bandwidth Crossover Frequency (fc) less than 10% of fsw