The SC4524A is a constant frequency peak current-mode
step-down switching regulator capable of producing 2A
output current from an input ranging from 3V to 28V. The
switching frequency of the SC4524A is programmable
up to 2MHz, allowing the use of small inductors and
ceramic capacitors for miniaturization, and high input/
output conversion ratio. The SC4524A is suitable for
next generation XDSL modems, high-definition TVs and
various point of load applications.
Peak current-mode PWM control employed in the
SC4524A achieves fast transient response with simple loop
compensation. Cycle-by-cycle current limiting and hiccup
overload protection reduces power dissipation during
output overload. Soft-start function reduces input start-
up current and prevents the output from overshooting
during power-up.
The SC4524A is available in SOIC-8 EDP package.
Wide input range: 3V to 28V
2A Output Current
200kHz to 2MHz Programmable Frequency
Precision V Feedback Voltage
Peak Current-Mode Control
Cycle-by-Cycle Current Limiting
Hiccup Overload Protection with Frequency Foldback
Soft-Start and Enable
Thermal Shutdown
Thermally Enhanced 8-pin SOIC Package
Fully RoHS and WEEE compliant
Applications
XDSL and Cable Modems
Set Top Boxes
Point of Load Applications
CPE Equipment
DSP Power Supplies
LCD and Plasma TVs
Typical Application Circuit
10V – 28V
C4
2.2mF
D1
1N4148
C1
0.1mF
L1
8.2mH
R4
42.2k
SS270 REV 4
Efficiency
V
90
85
80
5V/2A
OUT
IN
IN
BST
SW
Efficiency (%)
75
70
65
60
55
50
45
40
0
V
IN
= 12V
V
IN
= 24V
SS/EN
SC4524A
FB
COMP
C7
10nF
R7
28.0k
ROSC
GND
D2
20BQ030
R6
10.5k
C2
22mF
C8
10pF
R5
18.2k
C5
2.2nF
L1: Coiltronics DR73-8R2
C2: Murata GRM31CR60J226K
C4: Murata GRM31CR71H225K
0.5
1
1.5
2
Load Current (A)
Figure 1. 1MHz 10V-28V to 5V/2A Step-down Converter
June 26, 2008
Fig.1 Efficiency of the 1MHz 10V-28V to 5V/2A Step-Do
SC4524A
Pin Configuration
Ordering Information
Device
SC4524ASETRT
()(2)
SW
IN
ROSC
GND
1
2
3
4
9
8
7
6
5
BST
FB
COMP
SS/EN
Package
SOIC-8 EDP
Evaluation Board
SC4524AEVB
Notes:
() Available in tape and reel only. A reel contains 2,500 devices.
(2) Available in lead-free package only. Device is fully WEEE and RoHS
compliant.
(8 - Pin SOIC - EDP)
Marking Information
yyww=Date code (Example: 0752)
xxxxx=Semtech Lot No. (Example: E900)
2
SC4524A
Absolute Maximum Ratings
V
IN
Supply Voltage ……………………………… -0.3 to 32V
BST Voltage ……………………………………………… 42V
BST Voltage above SW …………………………………… 36V
SS Voltage ……………………………………………-0.3 to 3V
FB Voltage …………………………………………… -0.3 to V
IN
SW Voltage ………………………………………… -0.6 to V
IN
SW Transient Spikes (0ns Duration)……… -2.5V to V
IN
+.5V
Peak IR Reflow Temperature ………………………….
(2)
Thermal Information
Junction to Ambient
()
……………………………… 36°C/W
Junction to Case
()
…………………………………
5.5°C/W
Maximum Junction Temperature……………………… 50°C
Storage Temperature ………………………… -65 to +50°C
Lead Temperature (Soldering) 0 sec ………………… 300°C
Recommended Operating Conditions
Input Voltage Range ……………………………… 3V to 28V
Maximum Output Current ……………………………… 2A
Operating Ambient Temperature …………… -40 to +05°C
Operating Junction Temperature …………… -40 to +25°C
260°C
ESD Protection Level ………………………………… 2000V
Exceeding the above specifications may result in permanent damage to the device or device malfunction. Operation outside of the parameters specified in the
Electrical Characteristics section is not recommended.
NOTES-
() Calculated from package in still air, mounted to 3” x 4.5”, 4 layer FR4 PCB with thermal vias under the exposed pad per JESD5 standards.
(2) Tested according to JEDEC standard JESD22-A4-B.
Electrical Characteristics
Unless otherwise noted, V
IN
= 2V, V
BST
= 5V, V
SS
= 2.2V, -40°C < T
J
< 25°C, R
OSC
= 2.kΩ.
Parameter
Input Supply
Input Voltage Range
V
IN
Start Voltage
V
IN
Start Hysteresis
V
IN
Quiescent Current
V
IN
Quiescent Current in Shutdown
Conditions
Min
3
Typ
Max
28
Units
V
V
mV
V
IN
Rising
2.70
2.82
225
2.95
V
COMP
= 0 (Not Switching)
V
SS/EN
= 0, V
IN
= 2V
2
40
2.6
50
mA
µA
Error Amplifier
Feedback Voltage
Feedback Voltage Line Regulation
FB Pin Input Bias Current
Error Amplifier Transconductance
Error Amplifier Open-loop Gain
COMP Pin to Switch Current Gain
COMP Maximum Voltage
COMP Source Current
COMP Sink Current
V
IN
= 3V to 28V
V
FB
= V, V
COMP
= 0.8V
0.980
.000
0.005
-70
280
60
8
-340
.020
V
%/V
nA
µ
Ω
-
dB
A/V
V
µA
V
FB
= 0.9V
V
FB
= 0.8V, V
COMP
= 0.8V
V
FB
= .2V, V
COMP
= 0.8V
(Note )
I
SW
= -2.6A
2.6
2.4
7
25
Internal Power Switch
Switch Current Limit
Switch Saturation Voltage
3.3
250
4.3
400
A
mV
3
SC4524A
Electrical Characteristics (Cont.)
Unless otherwise noted, V
IN
= 2V, V
BST
= 5V, V
SS
= 2.2V, -40°C < T
J
< 25°C, R
OSC
= 2.kΩ.
Parameter
Minimum Switch On-time
Minimum Switch Off-time
Switch Leakage Current
Minimum Bootstrap Voltage
BST Pin Current
Conditions
Min
Typ
35
00
Max
Units
ns
ns
0
I
SW
= -2.6A
I
SW
= -2.6A
.8
60
2.3
95
µA
V
mA
Oscillator
Switching Frequency
R
OSC
= 2.kΩ
R
OSC
= 93.kΩ
R
OSC
= 2.kΩ, V
FB
= 0
R
OSC
= 93.kΩ, V
FB
= 0
.04
230
0
50
.3
300
230
00
.56
370
350
70
MHz
kHz
kHz
Foldback Frequency
Soft Start and Overload Protection
SS/EN Shutdown Threshold
SS/EN Switching Threshold
Soft-start Charging Current
Soft-start Discharging Current
Hiccup Arming SS/EN Voltage
Hiccup SS/EN Overload Threshold
Hiccup Retry SS/EN Voltage
0.2
0.3
.3
.7
.2
2.0
.5
2.8
0.4
.3
V
V
µA
µA
V
V
.2
V
V
FB
= 0 V
V
SS/EN
= 0 V
V
SS/EN
= .5 V
V
SS/EN
Rising
V
SS/EN
Falling
V
SS/EN
Falling
.0
2.5
.9
0.6
.0
Over Temperature Protection
Thermal Shutdown Temperature
Thermal Shutdown Hysteresis
Note : Switch current limit does not vary with duty cycle.
65
0
°C
°C
4
SC4524A
Pin Descriptions
SO-8
2
3
4
Pin Name
SW
IN
ROSC
GND
Pin Function
Emitter of the internal NPN power transistor. Connect this pin to the inductor, the freewheeling diode and the
bootstrap capacitor.
Power supply to the regulator. It is also the collector of the internal NPN power transistor. It must be closely by-
passed to the ground plane.
An external resistor from this pin to ground sets the oscillator frequency.
Ground pin
Soft-start and regulator enable pin. A capacitor from this pin to ground provides soft-start and overload hiccup
functions. Hiccup can be disabled by overcoming the internal soft-start discharging current with an external pull-
up resistor connected between the SS/EN and the IN pins. Pulling the SS/EN pin below 0.2V completely shuts off
the regulator to low current state.
The output of the internal error amplifier. The voltage at this pin controls the peak switch current. A RC compensa-
tion network at this pin stabilizes the regulator.
The inverting input of the error amplifier. If V
FB
falls below 0.8V, then the switching frequency will be reduced to
improve short-circuit robustness (see Applications Information for details).
Supply pin to the power transistor driver. Tie to an external diode-capacitor bootstrap circuit to generate drive
voltage higher than V
IN
in order to fully enhance the internal NPN power transistor.
The exposed pad serves as a thermal contact to the circuit board. It is to be soldered to the ground plane of the
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