NX2142ACUTR datasheet(14/18 Pages) MICROSEMI

14 / 18 page

NX2142/2142A

Rev. 1.1

10/28/07

B. Type II compensator design

If the electrolytic capacitors are chosen as

power stage output capacitors, usually the Type II

compensator can be used to compensate the sys-

tem.

For this type of compensator, F

O has to satisfy

LC<FESR<<FO<=1/10~1/5Fs.

Case 1:

Type II compensator can be realized by simple

RC circuit as shown in figure 13. R

3 and C1 introduce a

zero to cancel the double pole effect. C

introduces a

pole to suppress the switching noise.

To achieve the same effect as voltage amplifier,

the compensator of transconductance amplifier must

satisfy this condition: R

3>>1/gm and R1||R2>>1/gm.

The following equations show the compensator pole

zero location and constant gain.

Gain=

... (15)

F =

... (16)

... (17)

×π ××

≈

×π ××

compensator

loop gain

power stage

40dB/decade

20dB/decade

Gain

ESR

Figure 12 - Bode plot of Type II compensator

Vout

Vref

Figure 13 - Type II compensator with

transconductance amplifier(case 1)

The following parameters are used as an

example for type II compensator design, three

1500uF with 19mohm Sanyo electrolytic CAP

6MV1500WGL are used as output capacitors.

Coilcraft DO5010P-152HC 1.5uH is used as output

inductor. The power stage information is that:

VIN=12V, VOUT=1.2V, IOUT =12A, FS=600kHz.

1.Calculate the location of LC double pole F

and ESR zero F

ESR.

P13

5.3kHz 25nF

1.2k

×π ××

=Ω

Choose R

3 =1.2kΩ.

8. Calculate R

REF

OUT

REF

1.2k

0.8V

R =

381

-V

5V-0.8V

Ω×

=Ω

Choose R

1=381Ω.

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