ADP1822

Rev. B | Page 18 of 24

Compensation Using Both the ESR and Feed-Forward Zeros

Choose the compensation capacitor to set the compensation

the LC resonant frequency, or

()(

)

COMP

COMP

SW

CO

ZC

R

C

f

f

f

π

2

1

40

4

=

=

=

(34)

If the output capacitor ESR zero frequency falls between 1/2 of

the crossover frequency to 2× the crossover frequency, use the

circuit shown in Figure 18, such that the ESR zero along with a

feed-forward network stabilizes the regulator. In this case, the

feed-forward zero is set to 1/7 of the crossover frequency, and

the feed-forward pole is set to the same frequency as the ESR zero.

or

()(

)

COMP

COMP

LC

ZC

R

C

f

f

π

2

1

2

=

=

(35)

frequency by

()(

)

COMP

CO

COMP

R

f

C

π

2

4

=

(36)

(

)(

)(

)( )

LC

IN

CO

ZFF

RAMP

TOP

COMP

f

V

f

f

V

R

R

=

(44)

crossover frequency. Simplify the following equation:

In terms of the switching frequency and combining the constants,

()(

)

COMP

SW

COMP

R

f

C

37

.

6

≅

(37)

(

IN

SW

TOP

COMP

V

C

L

f

R

R

2

0705

.

0

≅

(45)

or

()(

)

COMP

LC

COMP

R

f

C

π

2

2

=

(38)

Choose the compensation capacitor to set the compensation

zero, f , to 1/2 of the LC resonant frequency, or

ZC

or whichever is greater.

zero at 1/7 of the crossover frequency

7

CO

ZFF

f

f

=

(39)

or

FF

TOP

CO

C

R

f

π

2

7

=

(40)

()( )

SW

TOP

FF

f

R

C

14

.

11

=

(41)

()

()( )

FF

FF

CO

C

R

f

π

2

7

1

=

(42)

FF

SW

FF

C

f

R

227

.

0

=

(43)

()(

)

COMP

COMP

LC

ZC

R

C

f

f

π

2

1

2

=

=

(46)

()(

)

COMP

LC

COMP

R

f

C

π

2

2

=

(47)

zero at 1/7 of the crossover frequency

7

CO

ZFF

f

f

=

(48)

or

FF

TOP

CO

C

R

f

π

2

7

=

(49)

()( )

SW

TOP

FF

f

R

C

14

.

11

=

(50)

()

()( )

FF

FF

CO

C

R

f

π

2

7

1

=

(51)

FF

SW

FF

C

f

R

227

.

0

=

(52)