13

 2005 Semtech Corp.

www.semtech.com

POWER MANAGEMENT

SC4502/SC4502H

0.62

0.5

12

0.3

1

0.5

12

5

1

D

=

+

−

+

−

=

Therefore

() (

)

3.18KHz

20Krads

F

10

10

2

1

p2

⇒

=

µ

⋅

Ω

≤

ω

−

and

()

43.4KHz

Krads

272

H

5.3

0.62

1

10

1

2

z2

⇒

=

µ

−

⋅

Ω

≥

ω

−

The spacing between p

converter is delivering the maximum output current from

the lowest V

This represents the worst-case

compensation condition. Ignoring C

moment, C

equivalent output resistance R

Ω

=

Ω

µ

=

=

−

4.7M

60

49dB

R

1

O

ctance

Transcondu

Gain

Loop

Open

Amplifier

60Hz

rads

380

560pF

4.7M

1

C

R

1

1

4

O

p1

⇒

=

•

Ω

=

=

ω

−

C

KHz

4.8

Krads

30.3

560pF

59K

1

C

R

1

1

4

3

z1

⇒

=

•

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 crossover frequency

should not be higher than

3

z

effect and maximizes loop bandwidth. Thus

OUT(MAX)

2

OUT

4

3

I

2

C

V

C

R

⋅

⋅

≈

(15)

R

Increasing R

crossover frequency. However it reduces the phase

margin. The values of R

Figure 8. Suggested PCB Layout for the SC4502/SC4502H. Notice that there is no

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

C3

VOUT

SHDN

R4

R3

C6

R2

VIN

GND

C4

R1

C5

C2

U1

C1

L1

D1

C3

VOUT

SHDN

R4

R3

C6

R2

VIN

GND

C4

R1

C5

C2

U1

C1

L1

D1

C3

VOUT

SHDN

R4

R3

C6

R2

VIN

GND

C4

R1

C5

C2

U1

C1

L1

D1

C3

VOUT

SHDN

R4

R3

C6

R2

VIN

GND

C4

R1

C5

C2

U1

C1

L1

D1

Applications Information