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PDF SC4524 Data sheet ( Hoja de datos )

Número de pieza SC4524
Descripción 2A Output 30V Step-Down Switching Regulator
Fabricantes Semtech Corporation 
Logotipo Semtech Corporation Logotipo



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POWER MANAGEMENT
Description
SC4524
Programmable Frequency, 2A Output
30V Step-Down Switching Regulator
Features
The SC4524 is an adjustable frequency peak current-
mode step-down switching regulator with an integrated
2.3A, 30V switch. The SC4524 can be programmed up
to 1.5MHz. This allows the use of small inductor and
ceramic capacitors, resulting in very compact power
supplies. The SC4524 is suitable for next generation XDSL
modems, set-top boxes and point of load applications.
The SC4524 uses peak current-mode PWM control for
www.DataeSaheseet4Uo.fcocmompensation. Cycle-by-cycle current limit and
hiccup overload protection reduce power dissipation
during overload. Combined soft start and enable pin not
only eliminates output start up overshoot but also allows
power sequencing.
u Up to 1.5 MHz Programmable Switching Frequency
u 2.3A Integrated Switch
u Wide Input Voltage Range 2.8V to 30V
u Peak Current-Mode Control with Cycle-by-Cycle
Current Limiting
u Hiccup Overload Protection
u Soft-Start and Enable
u Thermal Shutdown
u Thermally Enhanced 8-Pin SOIC Package
u Fully WEEE and RoHS Compliant
The SC4524 is available in SOIC-8 EDP package.
Applications
u XDSL and Cable Modems
u Set-top Boxes
u Point of Load Applications
u CPE Equipment
u DSP Power Supplies
u Disk Drives
Typical Application Circuit
V IN
24V
IN
SS BST
C7
22nF
SC4524 SW
C6
22pF
COMP
R5 ROSC
15.4k
C5
470pF
R3
17.4k
FB
GND
D1
C2 1N4148
0.1mF L1
4.7mH
OUT
R1 5V/2A
22.1k
C3
10mF
D2
20BQ030
C1 R2
22mF 5.49k
L1: Coiltronics FP3-4R7
C1: Murata GRM21BR60J226M
C3: Murata GRM32ER71H106K
90
85
80
75
70
65
60
55
50
0.0
Efficie ncy
0.5 1.0 1.5
Load Current (A)
2.0
Revision: December 30th, 2006
Figure 1. 1MHz 24V to 5V/2A Step-down Converter.
1
www.semtech.com

1 page




SC4524 pdf
SC4524
POWER MANAGEMENT
Block Diagrams
C OMP
6
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FB
7
SS
5
-
EA
+
+
PWM
-
1V 0.7V
REFERENCE
& THERMA L
SHUTDOW N
FAU L T
SLO PE
CO MP
+
S
+
SLOPE
C OMP
+
ISEN
-
+
IL IM
-
20m V
BST
8
S
Q
R
2 VIN
6 .3 m W
POWER
TR AN SIST OR
FB
Soft-Start
And
O verload
Hiccup
Control
1 SW
OVLD
4 GND
ROSC
3
SLOPE COMP
CLK
OS C IL L ATOR
Figure 2. SC4524 Functional Diagram
FB
0 .7 V
SS
+
-
1 .8 m A
1V/2 V
S
Q
R
OVLD
FAU L T
2 .6 m A
Figure 3. Details of the Soft-Start and Overload Hiccup Control Circuit
2006 Semtech Corp.
5
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SC4524 arduino
SC4524
POWER MANAGEMENT
Applications Information
duty-cycle invariant and are guaranteed higher than 2.3A.
The maximum load current is therefore conservatively
,
287 0$;
= ,/0
- D,/

= $ - D,/

(5)
10mF X5R ceramic capacitor is adequate. For high voltage
applications, a small ceramic (1mF or 2.2mF) can be
placed in parallel with a low ESR electrolytic capacitor to
satisfy both the ESR and bulk capacitance requirements.
Output Capacitor
If D,/ =  ¼,/0 , then
,www.DataShee2t48U7 .0co$m;
=
,
/0
-
D,
/

=,
-
,
/0
/0
=  ¼,/0 .
The saturation current of the inductor should be 20-30%
higher than the peak current limit (2.3A). Low-cost
powder iron cores are not suitable for high-frequency
switching power supplies due to their high core losses.
Inductors with ferrite cores should be used.
Power Line Input Capacitor
A buck converter draws pulse current with peak-to-peak
amplitude equal to its output current IOUT from its input
supply. An input capacitor placed between the supply
and the buck converter filters the AC current and keeps
the current drawn from the supply to a DC constant. The
input capacitance CIN should be high enough to filter the
pulse input current. Its equivalent series resistance (ESR)
should be low so that power dissipated in the capacitor
does not result in significant temperature rise and
degrade reliability. For a buck converter, the RMS ripple
current in the input capacitor is
,506 &,1 = ,287 '  - ' .
(6)
Power
dissipated
in
the
input
capacitor
is
,
506 &,1
¼ (65 .
Equation (6) has a maximum value
of
,287

( at
'
=


),
corresponding to the worst-case power dissipation
,287 ¼(65

in CIN.
Multi-layer ceramic capacitors, which have very low ESR
(a few mW) and can easily handle high RMS ripple current,
are the ideal choice for input filtering. A single 4.7mF or
The output ripple voltage DVOUT of a buck converter can
be expressed as
D9287
=
D,/ ÌÌÍË(65 +

I&287
ÜÜÝÛ
(7)
where COUT is the output capacitance.
Inductor ripple current DIL increases as D decreases
(Equation (3)). The output ripple voltage is therefore the
highest when VIN is at its maximum. The first term in (7)
results from the ESR of the output capacitor while the
second term is due to the charging and discharging of
COUT by the inductor ripple current. Substituting DIL =
0.69A, f = 500kHz and COUT = 22mF ceramic with ESR =
2mW in (7),
D9287 = $ ¼ PW + PW
= P9 + P9 = P9
Depending on operating frequency and the type of
capacitor, ripple voltage resulting from charging and
discharging of COUT may be higer than that due to ESR. A
10mF to 47mF X5R ceramic capacitor is found adequate
for output filtering in most applications. Ripple current
in the output capacitor is not a concern because the
inductor current of a buck converter directly feeds COUT,
resulting in very low ripple current. Avoid using Z5U and
Y5V ceramic capacitors for output filtering because these
types of capacitors have high temperature and high
voltage coefficients.
Freewheeling Diode
Use of Schottky barrier diodes as freewheeling rectifiers
reduces diode reverse recovery input current spikes,
easing high-side current sensing in the SC4524. These
diodes should have an average forward current rating
between 1A and 2A and a reverse blocking voltage of at
least a few volts higher than the input voltage. For
switching regulators operating at low duty cycles (i.e. low
ã 2006 Semtech Corp.
11
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