SC4808BIMSTRT datasheet(16/31 Pages) SEMTECH

16 / 31 page

 2005 Semtech Corp.

www.semtech.com

SC4808A/B

POWER MANAGEMENT

which might cause negative voltages at the output of the

drivers. This negative voltage can be clamped to a reason-

able level by placing a small Schottky diode directly at the

output of the driver as shown below.

C34

0.1u

VCC

SC1301A

C23

0.1u

SC1301A

VCC

R28

2.2u,16V

C26

D_A

0.1u,25V

C33

R33

10k

SYNC

SC4808

REF

LUVLO

SYNC

GND

OUTB

OUTA

VCC

D_B

Gate_A

Gate_B

R23

56.2k

Vin

OVER CURRENT

Two levels of over current protection are provided by the

SC4808. The current information is sensed at the CS pin

and compared to a peak current limit level of 525mV. If

the 525mV limit is exceeded, the OUTA and OUTB pulse

widths and duty cycle is reduced until the CS pin reaches a

second threshold of 950mV. At that point, the OUTA and

OUTB are disabled, and after a delay of 140µs, the inter-

nal softstart sequence is started. After the softstart dura-

tion (see page 21 for calculation of softstart time), normal

operation is achieved, unless the over current condition is

still present.

Application Information (Cont.)

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