IP1202 datasheet(20/29 Pages) IRF

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iP1202

Vref

Vo - Vref

More than one iteration may be required to calculate

the values of the compensation components if cross-

over frequencies higher than the range specified in

step 1 are required (for higher bandwidths and faster

transient response performance). To ensure stability

a phase margin greater than 45° shouldbe achieved.

Refer to AN-1043 for more detailed compensation

techniques using Transconductance Amplifiers.

Compensation in Current Share Mode

The iP1202 can be configured in single output paral-

leled configuration. The feedback loop of the first out-

put is closed around the output voltage, and the sec-

ond amplifier, which is also a transconductance one,

forces equal sharing of the inductor currents in both

outputs.

Voltage Loop

Type II and Type III methods of voltage loop com-

pensation discussed above, can be used to com-

pensate the voltage loop of a single output iP1202.

In this case, the total amount of capacitance seen

by both channels and the inductance of the voltage

controlling channel should be considered for com-

pensation.

Current Loop

Use the following procedure for current loop com-

pensation:

In Fig. 20, L

1 and L2 are the inductors for outputs 1

and 2 respectively. Rsh1 and Rsh2 are the current

sensing shunts for the same outputs.

7. Place the second pole f

p2 at or near fesr of the out-

put capacitor C

o and determine the value of R24 from

equation (20). Make sure R

24 <

8. Use equation (25) to calculate R

7 = R9 x

(25)

The crossover frequency f

0 for type III compensation

is represented by equation (24):

(24)

Follow the steps below to determine the feedback

loop compensation component values:

1. Select a zero db crossover frequency f

0 in the range

of 10% to 20% of the switching frequency f

sw.

2. Select R

23~ 10kΩ

3. Place the first zero f

z1 at 75% of the resonant fre-

quency f

LC of the output filter.

Determine C

9 from equation (22).

4. Place a third pole f

P3 at or near the switching fre-

quency f

SW.

Select C18 such that C

18 <

5. Calculate C

19 from equation (24).

6. Place the second zero at 125% of the resonant

frequency f

LC of the output filter. Calculate R9 using

equation (23).

ramp

The frequencies of the three poles and the two zeros

of the type III compensation scheme are represented

by the following equations:

p1= 0

(19)

(20)

(22)

(21)

(23)

≅

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