11

© 2006 Semtech Corp.

www.semtech.com

POWER MANAGEMENT

SC600

Applications Information (Cont.)

Mode Transition Impedance

The mode transition impedance Ro refers to the output

resistance of the charge pump before a transition to a

stronger mode occurs. Ro is dependent upon the frac-

tional charge pump, switching frequency, bucket capaci-

tor value, bucket capacitor ESR, and the internal switch

resistances.

Ro is proportional to,

1

fC

Ro can be measured to verify a low transition imped-

ance. Before measuring Ro, select the capacitors, set

the operating frequency and a constant load current. Find

the input voltage just before a weak to strong mode tran-

sition (i.e., 1.5x to 2x mode). Measure V

before the transition.

Ro will be,

Ro=

Table 2 -Ripple Performance (Cont.)

.

o

N

t

r

a

P]

z

H

k

[

.

q

e

r

FI

T

U

O

]

A

m

[]

p

-

p

V

m

[

e

l

p

p

i

R

t

u

p

t

u

O

e

d

o

m

x

5

.

1

]

p

-

p

V

m

[

e

l

p

p

i

R

t

u

p

u

O

e

d

o

m

x

2

C

T

U

O

]

F

μ

[C

T

E

K

C

U

B

]

F

μ

[

B

0

0

6

C

S

)

1

(

V

5

.

4

80

15

1

20

51

1

2

30

40

0

30

91

1

2

6

20

2

10

45

21

1

0

5

60

2

15

15

21

1

0

5

60

2

10

35

43

3

.

01

V

0

.

4

D

0

0

6

C

S

80

15

0

10

51

1

2

30

40

4

25

41

1

2

6

20

2

10

30

21

1

0

5

60

2

11

10

21

1

0

5

60

2

15

20

43

3

.

01

Note: (1) SC600C is very similar to SC600B.

A lower value of Ro will improve efficiency, so low ESR

ceramic capacitors are required. An X7R or X5R dielec-

tric is recommended. Y5V dielectric can require 2 to 3

times the rated value of an X7R dielectric for the same

performance over the operating temperature range.

Efficiency

Efficiency for the SC600 is defined as,

η =