14

© 2005 Semtech Corp.

www.semtech.com

POWER MANAGEMENT

SC4501

62

.

0

5

.

0

12

3

.

0

1

5

.

0

12

5

1

D

=

+

−

+

−

=

Therefore

(

)

(

)

KHz

68

.

4

Krads

4

.

29

F

10

8

.

6

2

1

2

p

=

=

µ

•

Ω

≤

ω

−

and

(

)

KHz

3

.

33

Krads

209

H

7

.

4

62

.

0

1

8

.

6

1

2

2

Z

=

=

µ

−

•

Ω

≥

ω

−

The spacing between p

converter is delivering the maximum output current from

the lowest V

condition. Ignoring C

low frequency pole with the equivalent output resistance

R

Ω

=

Ω

µ

=

=

−

M

7

.

4

60

dB

49

ce

tan

c

Transcondu

Gain

Loop

Open

Amplifier

R

1

O

Hz

41

rads

260

pF

820

M

7

.

4

1

C

R

1

1

4

O

1

p

−

=

−

=

•

Ω

−

=

−

=

ω

−

C

KHz

3

.

6

Krads

5

.

39

pF

820

K

9

.

30

1

C

R

1

1

4

3

1

Z

−

=

−

=

•

Ω

−

=

−

=

ω

−

The poles p

shift in the loop response. For stable operation, the overall

loop gain should cross 0dB with -20dB/decade slope. Due

to the presence of the RHP zero, the 0dB crossover frequency

should not be higher than

3

z

effect and maximizes loop bandwidth. Thus

)

MAX

(

OUT

2

OUT

4

3

I

2

C

V

C

R

≈

(15)

R

Increasing R

Application Information

Figure 9. Suggested PCB Layout for the SC4501. Notice that there is no via

directly under the device. All vias are 12mil in diameter.

U1

VOUT

SHDN

R1

C5

C1

L1

D1

VIN

U1

C3

R4

C4

R3

C6

R2

GND

C2

U1

VOUT

SHDN

SHDN

R1

C5

C1

L1

D1

VIN

U1

C3

R4

C4

R3

C6

R2

GND

C2