LSP5523

3A 27V Synchronous Buck Converter

9 of 15

www.liteonsemi.com

LSP5523 Rev. 04

2015/4/16

The feedback loop of the IC is stabilized by the components at the COMP pin, as shown in Figure 2. The DC

loop gain of the system is determined by the following equation:

COMP

VEA

OUT

VDC

G

A

I

V

A

925

.

0

=

1

1

2

COMP

VEA

EA

P

C

A

G

f

π

=

The second pole P2 is the output pole:

OUT

OUT

OUT

P

C

V

I

f

π

2

2

=

1

1

2

1

COMP

COMP

Z

C

R

f

π

=

2

COMP

COMP

3

P

C

R

π

2

1

f

=

The following steps should be used to compensate the IC:

V

G

G

f

C

V

R

COMP

EA

SW

OUT

OUT

COMP

925

.

0

10

2

•

=

π

)

(

637

.

0

1

F

fc

R

C

COMP

COMP

×

=

STEP3. If the output capacitor’s ESR is high enough to cause a zero at lower than 4 times the crossover frequency, an

ESRCOUT

R

1

≥

×

×

×

fs

R

C

ESR

OUT

π

(4)

(5)

(6)

(7)

(8)

(9)

(10)

(11)