IR3521 datasheet(35/45 Pages) IRF

35 / 45 page

IR3521

Page 35

V3.03

Type III Compensation for AVP Applications

Determine the compensation at no load, the worst case condition. Assume the RC, resistor and capacitor across

the output inductors, and L/DCR time constant matches, the crossover frequency and phase margin of the voltage

loop can be estimated by (22) and (23), where RLE is the equivalent resistance of inductor DCR.

DRP







(22)





180

)

tan(







(23)

Choose the desired crossover frequency fc around fc1, estimated by (22), or choose fc between 1/10 and 1/5 of

the switching frequency per phase. The components should be selected to ensure the close loop gain slope is

-20dB /Dec around the crossover frequency. Choose resistor RFB1 according to (24), and determine CFB and

CDRP from (25) and (26).

1 

(24)







(25)

DRP







)

(

(26)

RCP and CCP have limited effect on the crossover frequency, and are used only to fine tune the crossover

frequency and transient load response. Determine RCP and CCP from (27) and (28).

)

(







(27)





(28)

CCP1 is optional and may be needed in some applications to reduce the jitter caused by the high frequency noise.

A ceramic capacitor between 10pF and 220pF is usually enough.

Type III Compensation for Non-AVP Applications

Resistor RDRP and capacitor CDRP are not needed. Choose the crossover frequency fc between 1/10 and 1/5 of

the switching frequency per phase and select the desired phase margin θc. Calculate K factor from (29), and

determine the component values based on (30) to (34),

)]

180

(

tan[











(29)





)

(



(30)







(31)







(32)

IR3521 Datasheet(PDF) 35 Page - International Rectifier

IR3521 Datasheet(HTML) 35 Page - International Rectifier

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

Datasheet Download

Link URL