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PDF SC4503 Data sheet ( Hoja de datos )

Número de pieza SC4503
Descripción 1.3MHz Step-Up Switching Regulator
Fabricantes Semtech Corporation 
Logotipo Semtech Corporation Logotipo



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POWER MANAGEMENT
Description
The SC4503 is a 1.3MHz current-mode step-up switch-
ing regulator with an integrated 1.4A power transistor.
Its high switching frequency allows the use of tiny sur-
face-mount external passive components. The SC4503
features a combined shutdown and soft-start pin. The
optional soft-start function eliminates high input current
and output overshoot during start-up. The internal com-
pensation network accommodates a wide range of volt-
www.DataaSgheeetc4oUn.cvoemrsion ratios. The internal switch is rated at 34V
making the device suitable for high voltage applications
such as Boost and SEPIC.
The SC4503 is available in low-prole 5-lead TSOT-23 and
8-lead 2X2mm MLPD-W packages. The SC4503’s low
shutdown current (< 1μA), high frequency operation and
small size make it suitable for portable applications.
SC4503
1.3MHz Step-Up Switching
Regulator with 1.4A Switch
Features
‹ Low Saturation Voltage Switch: 260mV at 1.4A
‹ 1.3MHz Constant Switching Frequency
‹ Peak Current-mode Control
‹ Internal Compensation
‹ Programmable Soft-Start
‹ Input Voltage Range From 2.5V to 20V
‹ Output Voltage up to 27V
‹ Uses Small Inductors and Ceramic Capacitors
‹ Low Shutdown Current (< 1μA)
‹ Low Prole 5-Lead TSOT-23 and 8-Lead 2X2mm
MLPD-W packages
‹ Fully WEEE and RohS compliant
Applications
‹ Local DC-DC Converters
‹ TFT Bias Supplies
‹ XDSL Power Supplies
‹ Medical Equipment
‹ Digital Cameras
‹ Portable Devices
‹ White LED Drivers
TTyyppicicaal lAApppplilcicaatitoionnCCiricrcuuitit
VIN
L1 D1
VOUT
5V
4.7µH
10BQ015
12V, 0.5A
51
IN SW
C4 R1
15pF 432k
C1 SC4503
1µF OFF ON 4 SHDN/SS FB 3
C2
4.7µF
GND
2
R2
49.9k
C1: Murata GRM188R61A105K
C2: Murata GRM21BR61C475K
L1: Sumida CDC5D23B-4R7
Efficiency vs Load Current
95
1.3MHz
90
85
80
75
70
65
60
55 VOUT = 12V
50
0.001
0.010
0.100
Load Current (A)
1.000
Figure 1(a). 5V to 12V Boost Converter
May 4, 2007
Figure 1(b). Efciency of the 5V to 12V Boost Converter
1 www.semtech.com

1 page




SC4503 pdf
SC4503
POWER MANAGEMENT
Block Diagram
IN
5
SHDN/SS
4
www.DataSheet4U.com
FB
2
VOLTAGE
REFERENCE
1.25V
+
- EA
REF NOT READY
THERMAL
SHUTDOWN
TJ > 155°C
CLK
-
PWM
+
D1
Q1
+
Z1 1V
-
Q2
R
Q
S
+
ILIM
-
I-LIMIT
OSCILLATOR
+
Σ
+
SLOPE COMP
+
ISEN
-
SW
1
Q3
RSENSE
2
GND
Figure 2. SC4503 Block Diagram
2007 Semtech Corp.
5
www.semtech.com

5 Page





SC4503 arduino
SC4503
POWER MANAGEMENT
Applications Information (Cont.)
Switch on duty ratio in DCM is given by,
'=
/I
5
0 0

When the switch is turned on, the output capacitor supplies
the load current IOUT (Figure 4). The output ripple voltage
due to charging and discharging of the output capacitor
(11) is therefore:
Higher input current ripples and lower output current are
the drawbacks of DCM operation.
9287
=
,287'7
&287
(13)
Input Capacitor
www.DataSThheeeti4nUp.cuotmcurrent in a boost converter is the inductor cur-
rent, which is continuous with low RMS current ripples. A
2.2-4.7µF ceramic input capacitor is adequate for most
applications.
Output Capacitor
Both ceramic and low ESR tantalum capacitors can be
used as output ltering capacitors. Multi-layer ceramic
capacitors, due to their extremely low ESR (<5mΩ), are
the best choice. Use ceramic capacitors with stable
temperature and voltage characteristics. One may be
tempted to use Z5U and Y5V ceramic capacitors for output
ltering because of their high capacitance density and
small sizes. However these types of capacitors have high
temperature and high voltage coefcients. For example,
the capacitance of a Z5U capacitor can drop below 60%
of its room temperature value at –25°C and 90°C. X5R
ceramic capacitors, which have stable temperature and
voltage coefcients, are the preferred type.
The diode current waveform in Figure 4 is discontinuous
with high ripple-content. Unlike a buck converter in which
vthoeltaingdeu.cTthoer roipuptlpeucturrirpepnltevIoLldtaegteermofinaebsothoestoruetgpuultartioprplies
much higher and is determined by the absolute inductor
current. Decreasing the inductor ripple current does not
reduce the output ripple voltage appreciably. The current
flowing in the output filter capacitor is the difference
between the diode current and the output current. This
capacitor current has a RMS value of:
,287
9287
9,1

(12)
If a tantalum capacitor is used, then its ripple current rating
in addition to its ESR will need to be considered.
For most applications, a 10-22µF ceramic capacitor is suf-
cient for output ltering. It is worth noting that the output
ripple voltage due to discharging of a 10µF ceramic capaci-
tor (13) is higher than that due to its ESR.
Rectifying Diode
For high efciency, Schottky barrier diodes should be used
as rectifying diodes for the SC4503. These diodes should
have an average forward current rating at least equal to the
output current and a reverse blocking voltage of at least
a few volts higher than the output voltage. For switching
regulators operating at low duty cycles (i.e. low output
voltage to input voltage conversion ratios), it is benecial
to use rectifying diodes with somewhat higher average cur-
rent ratings (thus lower forward voltages). This is because
the diode conduction interval is much longer than that of
the transistor. Converter efciency will be improved if the
voltage drop across the diode is lower.
The rectifying diodes should be placed close to the SW
pin of the SC4503 to minimize ringing due to trace induc-
tance. Surface-mount equivalents of 1N5817 and 1N5818,
MBRM120, MBR0520L, ZHCS400, 10BQ015 and equiva-
lent are suitable.
Shutdown and Soft-Start
The shutdown ( SHDN SS ) pin is a dual function pin. When
driven from a logic gate with VOH>2V, the SHDN SS pin
functions as an on/off input to the SC4503. When the
shutdown pin is below 2V, it clamps the error amplier
output to 96+'1 66 and reduces the switch current limit.
Connecting RSS and CSS to the SHDN SS pin (Figure 5) slows
the voltage rise at the pin during start-up. This forces the
peak inductor current (hence the input current) to follow a
slow ramp, thus achieving soft-start.
2007 Semtech Corp.
11
www.semtech.com

11 Page







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