POWER MANAGEMENT
1
www.semtech.com
SC4503
1.3MHz Step-Up Switching
Regulator with 1.4A Switch in ThinSOT
PRELIMINARY
PRELIMINARY
PRELIMINARY
PRELIMINARY
PRELIMINARY
Features
Applications
Local DC-DC Converters
TFT Bias Supplies
XDSL Power Supplies
Medical Equipment
Digital Cameras
Portable Devices
White LED Drivers
The SC4503 is a 1.3MHz current-mode step-up switching
regulator with an integrated 1.4A power transistor. Its high
switching frequency allows the use of tiny surface-mount
external passive components. The SC4503 features a com-
bined shutdown and soft-start pin. The optional soft-start
function eliminates high input current and output over-
shoot during startup. The internal compensation network
of the SC4503 accommodates a wide range of voltage
conversion ratios. The internal switch is rated at 34V mak-
ing the SC4503 suitable for high voltage applications such
as Boost, SEPIC and Flyback.
The SC4503 is available in a low-profile 5-pin SOT-23 pack-
age. The SC4503's low shutdown current (< 1
A), high
frequency operation and small size make it suitable for
portable applications.
Typical Application Circuit
Low Saturation Voltage Switch: 260mV at 1.4A
1.3 MHz Constant Switching Frequency
Peak Current-mode Control
Internal Compensation
Soft-Start Function
Input Voltage Range From 2.5V to 20V
Output Voltage up to 32V
Uses Small Inductors and Ceramic Capacitors
Low Shutdown Current (< 1
A)
5-Lead Low Profile SOT-23 Package
Revision: October. 18th, 2005
1
F
C1
5V
VIN
VOUT
SC4503
3
1
5
2
GND
SHDN/SS
IN
SW
FB
4
ON
OFF
10BQ015
D1
L1
C2
4.7
F
R2
49.9K
R1
432K
12V, 0.5A
4.7
H
C4
15pF
Figure 1(a). 5V to 12V Boost Converter.
C1: Murata GRM188R61A105K
Figure 1(b). Efficiency of the 5V to 12V Boost Converter
Description
C2: Murata GRM21BR61C475K
L1: Sumida CDC5D23B-4R7
Efficiency vs Load Current
50
55
60
65
70
75
80
85
90
95
0.001
0.010
0.100
1.000
Load Current (A)
Ef
f
i
ciency (%
)
V
OUT
= 12V
1.35MHz
2
2005 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
SC4503
PRELIMINARY
PRELIMINARY
PRELIMINARY
PRELIMINARY
PRELIMINARY
Absolute Maximum Rating
Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified
in the Electrical Characteristics section is not implied.
Electrical Characteristics
Unless specified: V
IN
= V
SHDN/SS
= 3V, -40C < T
A
= T
J
< 85C
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.
0
V
3
2005 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
SC4503
PRELIMINARY
PRELIMINARY
PRELIMINARY
PRELIMINARY
PRELIMINARY
Pin Configurations
Ordering Information
Electrical Characteristics (Cont.)
TOP VIEW
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Notes:
(1) Only available in tape and reel packaging. A reel con-
tains 3000 devices.
(2) Lead free product. This product is fully WEEE and RoHS
compliant.
Unless specified: V
IN
= V
SHDN/SS
= 3V, -40C < T
A
= T
J
< 85C
IN
FB
GND
SW
SHDN/SS
5
4
1
2
3
5-LEAD TSOT-23
Pin Descriptions
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4
2005 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
SC4503
PRELIMINARY
PRELIMINARY
PRELIMINARY
PRELIMINARY
PRELIMINARY
Block Diagram
REF NOT READY
EA
-
FB
2
REFERENCE
VOLTAGE
IN
5
4
SHDN/SS
SHUTDOWN
THERMAL
1.25V
+
+
R
Q
S
PWM
CLK
-
+
+
+
-
ISEN
ILIM
+
-
I-LIMIT
GND
2
SW
1
OSCILLATOR
SLOPE COMP
R
SENSE
T > 160
C
J
1V
-
+
Q1
D1
Q2
Z1
Q3
Figure 2. SC4503 Block Diagram.
5
2005 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
SC4503
PRELIMINARY
PRELIMINARY
PRELIMINARY
PRELIMINARY
PRELIMINARY
Operation
The SC4503 is a 1.3MHz peak current-mode step-up
switching regulator with an integrated 1.4A (minimum)
power transistor. Referring to the block diagram in Figure
2, the clock CLK resets the latch and blanks the power
transistor Q
3
conduction. Q
3
is switched on at the trailing
edge of the clock. Switch current is sensed with an
integrated sense resistor. The sensed current summed
with the slope-compensating ramp is fed into the
modulating ramp input of the PWM comparator. The latch
is set and Q
3
conduction is terminated when the
modulating ramp intersects the error amplifier (EA)
output. If the switch current exceeds 2A (the typical
current-limit), then the current-limit comparator ILIM will
set the latch and turn off Q
3
. Due to separate pulse-
width modulating and current-limiting paths, cycle-by-
cycle current limit is unaffected by slope compensation.
Current-mode switching regulator is a dual-loop
feedback control system. In the inner current loop the
EA output controls the peak inductor current. In the outer
loop, the error amplifier regulates the output voltage.
The double reactive poles of the output LC filter are
reduced to a single real pole by the inner current loop,
allowing the internal loop compensation network to
accommodate a wide range of input and output voltages.
Applying 0.9V at the
SS
SHDN
pin enables the voltage
reference. The signal "REF NOT READY" does not go low
until V
IN
exceeds its minimum operating voltage (typically
2.2V). Assuming that an external resistor is placed
between the IN and the
SS
SHDN
pins during startup.
The voltage reference is enabled when the
SS
SHDN
voltage rises to 0.9V. Before V
IN
reaches 2.2V, "REF NOT
READY" is high. Q
2
turns on and the Zener diode Z
1
loosely
regulates the
SS
SHDN
voltage to 1V (above the reference
enabling voltage). The optional external resistor limits the
current drawn in this interval. When V
IN
exceeds 2.2V,
"REF NOT READY" goes low. Q
2
turns off, releasing
SS
SHDN
. If an external capacitor is connected from the
SS
SHDN
pin to the ground, the
SS
SHDN
voltage will
ramp up slowly. The error amplifier output, which is
clamped by D1 and Q1, follows the voltage at the
SS
SHDN
pin. The input inductor current, which is in turn
controlled by the error amplifier output, also ramps up
gradually. Soft-starting the SC4503 in this manner
eliminates high input current and output overshoot.
Under fault condition (V
IN
< 2.2V or over temperature),
the soft-start capacitor is discharged to 1V. When fault
condition disappears, soft-start re-initiates.
6
2005 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
SC4503
PRELIMINARY
PRELIMINARY
PRELIMINARY
PRELIMINARY
PRELIMINARY
Typical Application Circuits
Figure 3(a). Single Li-ion Cell to 5V Boost Converter.
L1: TDK VLF4012AT
Figure 3(b). Efficiency of the Single Li-ion Cell to 5V Boost
Converter.
VOUT
C1
4.7
F
SC4503
3
1
5
2
GND
SHDN/SS
IN
SW
FB
4
10BQ015
D1
L1
C2
10
F
R2
60.4K
R1
187K
5V
1.5
H
R3
15K
C3
56nF
2.6 - 4.2V
1-CELL
LI-ION
ON
OFF
3.3V
< 0.4V
C4
10pF
C1: Murata GRM188R60J475K
C2: Murata GRM21BR60J106K
Efficiency vs Load Current
50
55
60
65
70
75
80
85
90
95
0.001
0.010
0.100
1.000
Load Current (A)
E
ffi
c
i
e
n
c
y
(
%
)
V
OUT
= 5V
1.35MHz
V
IN
= 3.6V
V
IN
= 2.6V
V
IN
= 4.2V
Lower Trace : Inductor Current, 0.5A/div
40
s/div
Figure 3(c). Load Transient Response of the Circuit in Figure
3(a). I
LOAD
is switched between 0.1A and 0.5A.
Upper Trace : Output Voltage, AC Coupled, 0.2V/div
Lower Trace : Inductor Current, 0.5A/div
40
s/div
Figure 3(d). Load Transient Response of the Circuit in Figure
3(a). I
LOAD
is switched between 0.15A and 0.9A.
Upper Trace : Output Voltage, AC Coupled, 0.2V/div
V
IN
= 2.6V
V
IN
= 4.2V
7
2005 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
SC4503
PRELIMINARY
PRELIMINARY
PRELIMINARY
PRELIMINARY
PRELIMINARY
Semtech Corporation
Power Management Products Division
200 Flynn Road, Camarillo, CA 93012
Phone: (805)498-2111 FAX (805)498-3804
Contact Information
Land Pattern - TSOT-23
Outline Drawing - TSOT-23
0
.010
-
.004
.012
.003
(.024)
.018
-
.028
.000
-
-
-
.035
0.10
0.25
8
0
-
8
0.90
(0.60)
0.45
.024
.008
0.30
0.08
.043
.039
.004
0.00
0.70
-
0.20
0.60
-
0.10
1.10
1.00
-
-
1.90 BSC
.075 BSC
SEATING
aaa C
bbb
C A-B D
A
bxN
A2
A1
D
DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS
3.
OR GATE BURRS.
DATUMS AND TO BE DETERMINED AT DATUM PLANE
CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
-B-
NOTES:
1.
2.
-A-
-H-
SIDE VIEW
A
B
D
e1
e
C
H
PLANE
REFERENCE JEDEC STD MO-193, VARIATION AB.
4.
NOM
INCHES
DIMENSIONS
L1
ccc
aaa
bbb
01
N
DIM
c
e
e1
L
E1
E
D
A1
A2
b
A
MIN
MILLIMETERS
MAX MIN NOM MAX
.110 BSC
.037 BSC
DETAIL
ccc C
2X N/2 TIPS
2X E/2
5
SEE DETAIL
A
.008
1
2
N
E
.060
.114
.063
.118
.012
-
5
A
0.20
1.60
3.00
2.80 BSC
0.95 BSC
.067
1.50
2.90
.020
0.30
1.70
0.50
-
L
(L1)
c
01
0.25
PLANE
GAGE
2.80
.110
E1
DIMENSIONS
INCHES
Y
Z
DIM
G
P
X
C
MILLIMETERS
P
(C)
Z
Y
G
.055
.141
.031
(.087)
.037
.024
0.80
(2.20)
0.95
0.60
1.40
3.60
X
THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY.
CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR
COMPANY'S MANUFACTURING GUIDELINES ARE MET.
NOTES:
1.
DIMENSIONS
INCHES
Y
Z
DIM
G
P
X
C
MILLIMETERS
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