POWER MANAGEMENT
Application Information (Cont.)
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
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.
SC4808A/B
2005 Semtech Corp.
16
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