SC4524 Semtech Corporation, SC4524 Datasheet - Page 15

• Manufacturer Part Number: SC4524
• Description: 2A Output 30V Step-Down Switching Regulator
• Manufacturer: Semtech Corporation

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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.
POWER MANAGEMENT
Applications Information
2006 Semtech Corp.
2.4V
0.3V
0.7V
0.3V
0.7V
2V
1V
1V
1V
1V
2V
1V
0
0
0
0
V SS
V FB
Charge
Fast
V SS
Figure 9(b).
least 70% of its set
undergo shutdown
Output must be at
Switching Starts
voltage in this
interval or the
regulator will
and restart
(hiccup).
Switching
Start-up Fails due to (i) Short Soft-start Duration or (ii) Output Overload or (iii)
Output Short-circuited.
Enabled
V COMP
Hiccup
V FB
Figure 9(a). Normal Soft-start.
Not Switching
15
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 < V
shutdown latch in Figure 3 cannot be set. When V
exceeds 2V, the set input of the overload latch is no
Switching
Not Switching
SS
< 2V), the overload
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SC4524
SS