SC4524SETRT View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
SC4524SETRT Datasheet PDF : 21 Pages
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SC4524
POWER MANAGEMENT
Applications Information
start voltage ramp at the SS pin clamps the error amplifier
output (Figure 2). During regulator start-up, COMP voltage
follows the SS voltage. The converter starts to switch
when its COMP voltage exceeds 1.1V. The peak inductor
current gradually increases until the converter output
comes into regulation. Proper soft-start prevents output
overshoot during start-up. Current drawn from the input
supply is also well controlled. Notice that the inductor
current, not the converter output voltage, is ramped
during soft-start.
The soft-start capacitor is charged to a final voltage of
about 2.4V.
Overload / Short-Circuit Protection
The current limit comparator in the SC4524 limits the
peak inductor current to 3.2A (typical). The regulator
output voltage will fall if the load is increased above the
current limit. If overload is detected (the output voltage
falls below 70% of the set voltage), then the regulator
will be shut off. An internal 0.8µA current sink starts to
discharge the soft-start capacitor. As the soft-start
capacitor is discharged below 1V, the discharge current
source turns off and the soft-start capacitor is recharged
with a 1.8µA current source. The regulator undergoes
soft-start. During soft-start (1V < VSS < 2V), the overload
shutdown latch in Figure 3 cannot be set. When VSS
exceeds 2V, the set input of the overload latch is no
2.4V
2V
VSS
1V
Hiccup
Enabled
0.3V
0
Fast
Charge
1V
0.7V
Switching Starts
Output must be at
0
least 70% of its set
voltage in this
interval or the
regulator will
undergo shutdown
and restart
(hiccup).
VFB
Figure 9(a). Normal Soft-start.
2V
VSS
1V
0.3V
0
S wi tching
VCOM P
Not Switching
Swi tch in g
Not Switching
1V
0.7V
V FB
0
Figure 9(b). Start-up Fails due to (i) Short Soft-start Duration or (ii) Output Overload or (iii)
Output Short-circuited.
2006 Semtech Corp.
15
www.semtech.com
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