Programmable Frequency, 2A Output
30V Step-Down Switching Regulator
POWER MANAGEMENT
Description
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.
SC4524
Features
u
u
u
u
Up to 1.5 MHz Programmable Switching Frequency
2.3A Integrated Switch
Wide Input Voltage Range 2.8V to 30V
Peak Current-Mode Control with Cycle-by-Cycle
Current Limiting
Hiccup Overload Protection
Soft-Start and Enable
Thermal Shutdown
Thermally Enhanced 8-Pin SOIC Package
Fully WEEE and RoHS Compliant
u
u
u
The SC4524 uses peak current-mode PWM control for
ease of compensation. Cycle-by-cycle current limit and
u
hiccup overload protection reduce power dissipation
u
during overload. Combined soft start and enable pin not
only eliminates output start up overshoot but also allows
power sequencing.
The SC4524 is available in SOIC-8 EDP package.
Applications
u
u
u
u
u
u
XDSL and Cable Modems
Set-top Boxes
Point of Load Applications
CPE Equipment
DSP Power Supplies
Disk Drives
Typical Application Circuit
Efficiency
90
V IN
24V
85
IN
D1
SS
C7
22nF
BST
Efficiency (%)
C2
1N4148
0.1mF
L1
80
OUT
5V/2A
R1
22.1k
SC4524
COMP
SW
75
70
65
60
55
4.7mH
FB
C6
22pF
R5
15.4k
C5
470pF
ROSC
R3
17.4k
GND
C3
10mF
D2
20BQ030
C1
22mF
R2
5.49k
L1: Coiltronics FP3-4R7
C1: Murata GRM21BR60J226M
C3: Murata GRM32ER71H106K
50
0.0
0.5
1.0
1.5
2.0
Load Current (A)
Figure 1. 1MHz 24V to 5V/2A Step-down Converter.
Revision: December 30th, 2006
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SC4524
POWER MANAGEMENT
Absolute Maximum Ratings
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.
Parameter
Input Voltage
BST Pin
BST Pin Above SW
SS Pin
FB Pin
SW Voltage
SW Transient Spikes (<10ns Duration)
Operating Ambient Temperature Range
Thermal Resistance Junction to Ambient
Thermal Resistance Junction to Case
Maximum Junction Temperature
Storage Temperature Range
Lead Temperature (Soldering)10 sec
ESD Rating (Human Body Model)
Notes: This device is ESD sensitive. ESD handling precaution is required.
Symbol
V
IN
V
BST
V
BST
-V
SW
V
SS
V
FB
V
SW
V
SW
T
A
θ
JA
θ
JC
T
J
T
STG
T
LEAD
ESD
Max
-0.3 to 32
42
24
3
-0.3 to V
IN
-0.6 to V
IN
V
IN
+1.5
-2.5
-40 to 85
36
5.5
150
-65 to +150
300
1500
Units
V
V
V
V
V
V
V
°C
°C/W
°C/W
°C
°C
°C
V
Electrical Characteristics
Unless specified: -40°C < T
A
< 85°C, -40°C < T
J
< 105°C, R
OSC
= 12.1kΩ, V
IN
= 5V, V
BST
= 8V
Parameter
Maximum Operating V
IN
V
IN
Start Voltage
V
IN
Start Hysteresis
V
IN
Quiescent Current
V
IN
Quiescent Current in Shutdown
Feedback Voltage
Feedback Voltage Line Regulation
FB Pin Input Bias Current
Error Amplifier Transconductance
2006 Semtech Corp.
Conditions
Min
Typ
Max
30
Units
V
V
mV
2.45
2.62
75
2.78
Not switching
V
SS
= 0V
0.980
V
IN
= 3V to 30V
V
FB
= 1V, V
COMP
= 1.5V
2
3.5
40
1.000
0.005
-15
280
5
60
1.020
mA
µA
V
%/ V
-30
nA
µΩ
-1
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SC4524
POWER MANAGEMENT
Electrical Characteristics (Cont.)
Unless specified: -40°C < T
A
< 85°C, -40°C < T
J
< 105°C, R
OSC
= 12.1kΩ, V
IN
= 5V, V
BST
= 8V
Parameter
Error Amplifier Open-Loop Gain
COMP Source Current
COMP Sink Current
COMP Pin to Switch Current Gain
COMP Switching Threshold
COMP Maximum Voltage
Switching Frequency
Maximum Duty Cycle
Switch Current Limit
Switch Saturation Voltage
Switch Leakage Current
Minimum BST Voltage
BST Pin Current
Minimum Soft-Start Voltage to Exit
Shutdown
Soft-start Charging Current
Soft-start Discharging Current
Minimum Soft-start Voltage to
Enable Overload Shutoff
FB Overload Threshold
Soft-start Voltage to Restart
Switching After Overload Shutoff
Thermal Shutdown Temperature
Thermal Shutdown Hysteresis
Conditions
Min
Typ
53
Max
Units
dB
µA
µA
A/V
V
FB
= 0.8V, V
COMP
= 1.5V
V
FB
= 1.2V, V
COMP
= 1.5V
20
20
8
0.7
1.1
2.2
1.2
1.4
90
3.2
0.3
10
1.6
1.3
V
V
MHz
%
A
V
µA
V
mA
mA
V
FB
= 0.9V
(Note 2)
(Note 1)
I
SW
= -2A
80
2.3
I
SW
= -2A
I
SW
= -0.5A
I
SW
= -2A
0.2
V
S S
= 0V
V
SS
= 1.5V
V
SS
= 1.5V
V
SS
Rising
V
SS
= 2.3V, V
FB
Falling
V
SS
Falling
0.7
1.8
20
60
0.4
2
1.8
0.8
2
0.7
1
155
10
2.5
0.7
V
µA
µA
µA
V
V
1.3
V
°C
°C
Notes: (1) Guaranteed by design, not tested in production.
(2) The maximum duty cycle specified corresponds to 1.4MHz switching frequency. Duty cycles higher than those specified can be
achieved by lowering the operating frequency.
2006 Semtech Corp.
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SC4524
POWER MANAGEMENT
Pin Configuration
TOP V IEW
SW
VIN
ROSC
GND
Ordering Information
Part Number
SC4524SETRT
(1)(2)
BST
FB
COMP
SS
P ackag e
SOIC-8 EDP
Evaluation Board
1
2
3
4
8
7
6
5
S C 4524E V B
(8 Pin SOIC -EDP)
Underside metal must be soldered to ground.
Notes:
(1) Only available in tape and reel packaging. A reel contains
2500 devices.
(2) Lead free product. This product is fully WEEE and RoHS
compliant.
Pin Descriptions
SO-8EDP
1
2
3
4
Pin Name
SW
VIN
ROSC
GND
Pin Function
The emi tter of the i nternal NP N power transi stor. C onnect thi s pi n to the i nductor and the
freewheeling diode.
Power supply to the SC4524. It is also connected to the collector of the internal NPN power
transistor. It must be bypassed with a ceramic capacitor to ground.
Frequency setting pin. An external resistor from his pin to the ground sets the oscillator frequency.
Ground pin.
Soft start and enable pin.
(1). A capacitor from SS pin to the ground provides soft-start and overload hiccup functions. Soft
start is recommended for all applications.
(2). Pulling SS pin below 0.4V shuts off the regulator and reduces the input supply current to
40uA at 5V.
Compensation pin. It is also the output of the internal error amplifier.
(1). A RC network at this pin compensates the control loop.
(2). The voltage at this pin controls the peak current of the internal switch.
The output voltage feedback pin. It is also the inverting input of the error amplifier.
Supply pin to the power transistor driver. Tie to external bootstrap circuit to generate a local
supply voltage higher than the input voltage in order to fully turn on the internal power transistor.
The exposed pad at the bottom of the package is electrically connected to the ground pin of the
SC4524. It also provides a thermal contact to the circuit board. It has to be soldered to the analog
ground of the PC board.
5
SS
6
7
8
Metal
P ad
COMP
FB
BST
2006 Semtech Corp.
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SC4524
POWER MANAGEMENT
Block Diagrams
2
VIN
S
+
+
+
ILIM
-
+
ISEN
-
6.3mW
20m V
BST
8
SLOPE
COMP
COMP
6
FB
7
-
EA
+
SS
5
+
PWM
-
S
Q
R
POWER
TRANSISTOR
FB
1
SW
1V
0.7V
REFERENCE
& THERMA L
SHUTDOW N
FAULT
Soft-Start
And
O verload
Hiccup
Control
OVLD
SLO PE
COMP
4
GND
SLOPE COMP
ROSC
3
OSCILLATOR
CLK
Figure 2. SC4524 Functional Diagram
FB
0.7V
SS
+
-
1.8mA
S
Q
R
OVLD
1V/2 V
FAULT
2.6mA
Figure 3. Details of the Soft-Start and Overload Hiccup Control Circuit
2006 Semtech Corp.
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