NX2142ACUTR datasheet(15/18 Pages) MICROSEMI

15 / 18 page

NX2142/2142A

Rev. 1.1

10/28/07

×π ××

OUT

1.5uH 4500uF

1.94kHz

×π ××

×π ×

Ω×

ESR

OUT

ESRC

6.33m

4500uF

5.6kHz

2.Set crossover frequency FO=60kHz>>F

ESR.

3. Set R

2 equal to 4kΩ. Based on output

voltage, using equation 21, the final selection of R

1 is

Ω.

4.Calculate R

3 value by the following equation.

OS CO

R =R

ESR

60kH z

1 .5uH

1 0

6 .33m

=36k

×π ××

××

×π ××

×Ω

Ω

Choose R

3 =37.4kΩ.

5. Calculate C

1 by setting compensator zero FZ

at 75% of the LC double pole.

C =

37.4k

0.75 1.94kHz

=2.7nF

×π ××

×π ×

Ω××

Choose C

1=2.7nF.

6. Calculate C

2 by setting compensator pole

at half the swithing frequency.

C =

37 .4 k

600k Hz

=14pF

π ××

π ×

Ω×

Choose C

2=15pF.

Case 2:

Type II compensator can also be realized by

simple RC circuit without feedback as shown in figure

15. R

3 and C1 introduce a zero to cancel the double

pole effect. C

2 introduces a pole to suppress the switch-

ing noise. The following equations show the compen-

sator pole zero location and constant gain.

Gain=g

... (18)

R +R

F =

... (19)

... (20)

××

×π ××

≈

×π ××

Vout

Vref

Figure 14 - Type II compensator with

transconductance amplifier(case 2)

The following is parameters for type II compen-

sator design. Input voltage is 12V, output voltage is

2.5V, output inductor is 2.2uH, output capacitors are

two 680uF with 41m

Ω electrolytic capacitors.

1.Calculate the location of LC double pole F

and ESR zero F

ESR.

×π ××

OUT

2.2uH 1360uF

2.9kHz

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