IP1201 datasheet(20/29 Pages) IRF

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iP1201

(21)

3. Place a zero at 75% of f

LC to cancel one of the LC

filter poles.

(13)

4. Calculate C

9 using equations (11) and (13)

Calculation of compensation components for out-

put1, based on the example above yields:

LC = 4.0kHz

z = 3.0kHz

0 = 20kHz (based on Fsw = 200kHz)

esr = 10kHz, per equation (7) using Resr = 11mΩ.

5 = 4.5K

9 = 12nF

The same steps can be used to determine the val-

ues of the compensation components for output2.

Sometimes, a pole f

p2 is added at half the switching

frequency to filter the switching noise. This is done

by adding a capacitor C

opt in Fig.20 from the output of

the error amplifier (CC pin of iP1201) to ground. This

pole is given by equation (14):

(14)

Select C

opt such that:

opt ≤

(15)

Type III

Type III compensation scheme allows the use of

any type of capacitors with esr frequency of any range.

This scheme suggests a double pole double zero

compensation and requires more components

around the error amplifier to achieve the desired

gain and phase margins. Fig. 21 represents the type

III compensation network for iP1201.

The transfer function of the type III compensator is

given by eqaution (16)

)

(

)

(

)

(

)

(

)

(

≈

(16)

C10

E/A1

Vout1

FB1

VREF

CC1

iP1201

R26

C22

R25

C21

Magnitude(dB)

Frequency

H(s) dB

Fig. 21: Typical Type III compensation and its gain

plot

The frequencies of the three poles and the two zeros

of the type III compensation scheme are represented

by the following equations:

p1= 0

(17)

(18)

opt

≈

(20)

(19)

≅

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