SC4808B-1 查看數據表（PDF） - Semtech Corporation

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SC4808B-1

High Performance Dual Ended PWM Controller

Semtech Corporation 

POWER MANAGEMENT

Application Information (Cont.)

It should be noted that if high speed/high current drivers

such as the SC1301 are used, careful layout guide lines

must be followed in order to minimize stray inductance,

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.

C23

F

VCC

0.1u

C26

2.2u,16V

U4

5 REF

GND 6

4 FB

OUTB 7

3 CS

OUTA 8

2 RC

VCC 9

1 SYNC

LUVLO 10

SC4808

SYNC

56.2k

R28

10

C33

0.1u,25V

C34

0.1u

10k

Vin

R23

R33

VCC EN

SC1301A

3 5 U3

1

2

4

Gate_B

D_B

VCC EN

SC1301A

3 5 U6

1

2

4

Gate_A

D_A

OVER CURRENT

Two levels of over current protection are provided by the

SC4808B-1. 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 18 for calculation of softstart time), normal

operation is achieved, unless the over current condition is

still present.

 2006 Semtech Corp.

13

SC4808B-1

www.semtech.com

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