SC46208

enough attenuation time for inductor, thus prevent it from running away. When the output voltage increases, the

frequency increases to 1.25MHz gradually.

Over Voltage Detection

When the over-voltage detect circuit detects the output voltage is more than 6% of the set value, it will shutdown

the PMOS switch to prevent the output voltage from over-shoot until the voltage drops to set value.

Current Limit and Thermal Shutdown

Current limit is implemented through internal comparator, it limits the PMOS current in the 1.5A in one cycle,

thus to protect the SC46208 in over load condition.

When the die temperature is over 150

°C due to the long time over load operation, SC46208 is shutdown

automatically until the temperature lower to normal state, the hysteresis temperature during this period is about

20

°C.

APPLICATION NOTES

Inductor Selection

The SC46208 can utilize small surface mount and chip inductors due to its fast 1.25MHz switching frequency.

For most applications the SC46208 operates with inductors of 1μH to 4.7μH. The large inductance will decrease

the ripple current, but high inductance values will also increase the PCB size, and the low inductance value result

HANGZHOU SILAN MICROELECTRONICS CO.,LTD

REV:1.1

2008.09.10

Http://www.silan.com.cn

Page 5 of 11

IN

OUT

OUT

IN

ripple

V

V

L

V

V

fs

1

I

×

−

×

=

LOAD(max)

I

sat

I

The rating current of inductor is equal to half of the max. load current adds half the max. ripple current ,to handle

the peak inductor current without saturating. Choose inductor ripple current

approximately 40% of the

maximum load current

, so the rating current

satisfied with following formula:

ripple

I

LOAD(max)

ripple

LOAD(max)

sat

20%)I

(1

I

2

1

I

I

+

=

+

>

The max. load current is 600mA, for most applications, the inductor of 720mA rating value is enough; for higher

efficiency, please choose an inductor with low DC series resistance (DCR). To reduce the noise, use a shielded

bobbin inductor.

Capacitor Selection

The low ESR capacitor is required to keep the output voltage ripple small. There, the multilayer ceramic

capacitor is recommended due to their low ESR and small size. In the most applications, 10-22

μF output

capacitors are enough, higher capacitor can be used to reduce the output ripple and improve transient

response.

The low ESR input capacitor reduces the surge current drawn from the input and switching noise from the

device. Ceramic capacitor is the best selection for input capacitor, and the capacitor should be as near as

possible to chip. A 4.7μF ceramic capacitor is sufficient for most applications.

Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and small

temperature coefficients.