SC4521
3A Step-Down Switching Regulator
with Programmable Soft Start
POWER MANAGEMENT
Description
Features
The SC4521 is a current mode switching regulator with
an integrated switch, operating at 600kHz with
programmable soft start and enable functions. The
integrated switch allows for cost effective low power
solutions (peak switch current 3 amps). High frequency
operation allows for very small passive components.
Current mode operation allows for fast dynamic response
and instantaneous duty cycle adjustment as the input
varies (ideal for CPE applications where the input is a
wall plug power).
The low shutdown current makes it ideal for portable
applications where battery life is important.
Wide operating voltage range: 4.4V to 24V
Integrated 3 Amp switch
600kHz frequency of operation
Programmable soft start funchion
Current mode control
Precision enable threshold
SO-8 EDP Lead-free package, fully WEEE and RoHS
compliant
Applications
The SC4521 is an 600kHz switching regulator with a low
pin count.
XDSL modems
CPE equipment
DC-DC point of load applications
Portable equipment
Digtial consumer electronics
The SC4521 allows customers to use large capacitive
loads because its programmable soft start limits the dv/
dt of the output at start up.
Typical Application Circuit
D1
C1
1
2
VIN
5
Enable
C3
8
C6
BST
IN
EN
SS
SW
SC4521
GND
4
FB
COMP
L1
3
VOUT
6
R1
7
C4
C2
D2
R2
R3
Revision: October 5, 2007
1
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SC4521
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. Exposure to Absolute Maximum rated conditions for extended periods of time may
affect device reliability.
Parameter
Symbol
Limits
Units
Input Supply Voltage
VIN
-0.3 to +28
V
Boost Pin Above VSW
(VBST - VSW)
16
V
Boost Pin Voltage
V BST
-0.3 to +32
V
EN Pin Voltage
V EN
-0.3 to +24
V
FB Pin Voltage
V FB
-0.3 to +6
V
FB Pin Current
IFB
1
mA
SS Pin Voltage
V SS
+3
V
Thermal Impedance Junction to Ambient (1)
θJA
36.5
°C/W
Maximum Junction Temperature
TJ
150
°C
Storage Temperature Range
TSTG
-65 to +150
°C
Lead Temperature (Soldering) 10 sec
TLEAD
300
°C
ESD Rating (Human Body Model)
ESD
2
kV
Note: (1) ThetaJA is calculated from a package in still air, mounted to 3" x 4.5", 4 layer FR4 PCB with thermal vias under
exposed pad per JESD51 standards.
Electrical Characteristics
Unless specified: VIN = 12V, VCOMP = 0.8V, VBST = VIN + 5V, EN = tied to VIN, SW = open.
TA = TJ = -40°C to 125°C.
Parameter
Symbol
Operating Input Voltage
VIN
Maximum Switch Current Limit
ISW
Oscillator Frequency
fOSC
Conditions
TA = 25°C, D = 50%
Min
Typ
3.5
500
600
Switch On Voltage Drop
VD(SW)
ISW = 3A
220
VIN Rising Undervoltage Lockout
VUVLO
TJ = 0°C to 85°C
3.9
VIN UVLO Hysteresis
VHYST
VIN Supply Current
Max
Units
24
V
5.5
A
700
kHz
mV
4.4
60
V
mV
IQ
V FB = 1V
3
IQ(OFF)
V E N = 0V
250
µA
Thermal Shutdown Trip Point
155
°C
Thermal Shutdown Hysteresis
10
°C
Standby Current
2007 Semtech Corp.
2
5.5
mA
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SC4521
POWER MANAGEMENT
Electrical Characteristics (Cont.)
Unless specified: VIN = 12V, VCOMP = 0.8V, VBST = VIN + 5V, EN = tied to VIN, SW = open.
TA = TJ = -40°C to 125°C.
Parameter
Symbol
FB Input Current
IFB
Feedback Voltage
V FB
Conditions
Min
0.784
4.4V < VIN < 24V(1)
Feedback Voltage Line
Regulation
FB to VCOMP Voltage Gain(2)
FB to VCOMP
Transconductance(2)
Typ
Max
Units
-0.25
-1
µA
0.8
0.816
V
+3
mV/V
V/V
0.9V ≤ VCOMP ≤ 2.0V
150
350
∆ ICOMP = ± 10µA
500
850
1300
µMho
VCOMP Pin Source Current
VFB = 0.6V
70
110
µA
VCOMP Pin Sink Current
VFB = 1.0V
-70
-110
µA
VCOMP = 1.25V
4.3
A/V
Duty cycle = 0%
0.6
V
VCOMP OCP Threshold
VCOMP rising
2
V
VCOMP Hiccup Retry Threshold
VCOMP falling
0.25
V
VCOMP Pin to Switch Current
Transconductance
VCOMP Pin Maximum Switching
Threshold
Maximum Switch Duty Cycle
DMAX
VCOMP = 1.2V, ISW = 400mA
85
%
2.7
Minimum Boost Voltage Above
Switch(2)
Boost Current
V
ISW = 1A
10
15
ISW = 3A
30
45
1.27
1.5
1.1
mA
V
Enable Input Threshold Voltage
VETH
Enable Output Bias Current
IEOL
EN = 50mV below threshold
8
µA
IEOH
EN = 50mV below threshold
10
µA
Soft Start Charging Current (3)
ISS
V SS = 0
16
µA
Soft Start Discharging Current
ISS
-2
mA
Notes:
(1) The required minimum input voltage for a regulated output depends on the output voltage and load condition.
(2) Guaranteed by design.
(3) See Application Information.
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SC4521
POWER MANAGEMENT
Pin Configurations
Ordering Information
TOP VIEW
BST
1
8
SS
IN
2
7
COMP
SW
3
6
FB
GND
4
5
EN
Part Number (1)(2)
P ackag e
SC4521SETRT
SOIC-8L-EDP
S C 4521E V B
EVALUATION BOARD
Notes:
(1) Only available in tape and reel packaging. A reel
contains 2500 devices.
(2) Lead free product. This product is WEEE and
RoHS compliant.
(SOIC-8L-EDP)
Pin Descriptions
Pin #
Pin Name Pin Function
1
BST
This pin provides power to the internal NPN switch. The minimum turn on voltage for this switch
is 2.7V.
2
IN
Pin IN delivers all power required by control and power circuitry. This pin sees high di/dt during
switching. A decoupling capacitor should be attached to this pin as close as possible.
3
SW
Pin SW is the emitter of the internal switch. The external freewheeling diode should be connected
as close as possible to this pin.
4
GND
All voltages are measured with respect to this pin. The decoupling capacitor and the freewheeling
diode should be connected to GND as short as possible.
5
EN
This is the chip enable input. The regulator is switched on if EN is high, and it is off if EN is low.
The regulator is in standby mode when EN is low, and the input supply current is reduced to a few
microamperes.
6
FB
Feedback input for adjustable output controllers.
7
COMP
8
SS
-
Thi s i s the output of the i nternal error ampli fi er and i nput of the peak current comparator. A
compensation network is connected to this pin to achieve the specified performance.
Soft start pin. An external capacitor connected from this pin to GND sets the soft start time.
THERMAL P ad for heatsi nki ng purposes. C onnect to ground plane usi ng multi ple vi as. Not connected
PAD
internally.
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SC4521
POWER MANAGEMENT
Block Diagram
+
+
Is
IN
ISEN
+
40m
SLOPE
COMP
BST
-
FB
+
PWM
S
EA
Q
POWER
TRANSISTOR
R
SW
Is
REFERENCE
EN
UVLO
1.6V INTERNAL SUPPLY
SS
GND
OL
HICCUP
SLOPE
FB
SLOPE COMP
OSCILLATOR
FREQUENCY
CLK
Typical Characteristic - OCP Limit
SC4519H OCP Limit vs Duty Cycle
7
6.5
6
Current Limit (A)
5.5
5
ILIM @-40C
4.5
ILIM @25C
ILIM @125C
4
3.5
3
2.5
2
0
20
40
60
80
100
Duty Cycle (%)
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SC4521
POWER MANAGEMENT
Application Information
about 2V. When an OCP fault is detected, the switch is
turned off and the external COMP capacitor is gradually
discharged at the rate of dv/dt=3µA/Ccomp. Ccomp is
the total capacitance value attached to COMP. At the
same time, the soft start cap CSS is quickly discharged.
Once the COMP voltage has fallen below 250mV, the
part enters a normal startup cycle. In the case of
sustained overcurrent or dead-short, the part will
continually cycle through the retry sequence as described
above.
The SC4521 is a current mode buck converter regulator.
The SC4521 uses two feedback loops that control the
duty cycle of the internal power switch. The error amplifier
functions like that of the voltage mode converter. The
output of the error amplifier works as a switch current
reference. This technique effectively removes one of the
double poles in the voltage mode system. With this, it is
much simpler to compensate a current mode converter
to have better performance.
Soft Start
Enable
Internally, connected to the SS pin is a 100K pull-up
resistor from an internal 1.6V regulator and the collector
of an NPN pull-down transistor from SS to GND. The NPN
transistor is “on” when the Enable pin is low or when a
fault is detected (Input UVLO, Over-Current, or Over
Temp). When the SC4521 is disabled or when a fault is
detected, the NPN transistor pulls the SS pin low. The
SS charging time is controlled by the internal 100k
resistor and external soft-start cap. This is a closed-loop
soft-start which effectively “ramps the reference”. The
SS process completes when the SS pin voltage is
exceeds the internal reference voltage, 0.8V. The SS pin
continues to charge up to 1.6V, well above the reference
voltage to ensure it does not interfere with normal
operation. The governing SS equation is:
Pulling and holding the EN pin below 0.4V activates the
shut down mode of the SC4521 which reduces the input
supply current to 250µA. During the shut down mode,
the switch is turned off. The SC4521 is turned on if the
EN pin is pulled high.
Oscillator
Its internal free running oscillator sets the PWM frequency
at 600kHz for the SC4521 without any external
components to program the frequency.
UVLO
TSS = 69000 • CSS
For example, a 22nF SS cap would give a SS time of
approximately 1.5mS.
When the EN pin is pulled and held above 1.8V, the voltage
on Pin IN determines the operation of the SC4521. As
VIN increases during power up, the internal circuit senses
VIN and keeps the power transistor off until VIN reaches
4.4V.
However, when VI is higher than about 13V, the SC4521
requires a pull-up resistor from the SS pin to VI for normal
operation. The softstart time can be estimated as:
TSS = R SS ⋅ C SS ⋅ [ − Ln (1 −
Load Current
0 .8
)]
VI
The peak current IPEAK in the switch is internally limited.
For a specific application, the allowed load current IOMAX
will change if the input voltage drifts away from the original
design as given for continuous current mode:
Where:
Rss = pull-up resistance from SS pin to VI,
Css = capacitance from SS pin to GND, and
VI = input voltage.
IOMAX = 3 −
Where:
fs = switching frequency,
Vo = output voltage and
D = duty ratio, VO/VI
VI = input voltage.
Overcurrent Protection
The current sense amplifier in the SC4521 monitors the
switch current during each cycle. Overcurrent protection
(OCP) is triggered when the current limit exceeds the upper
limit of 3A, detected by a voltage on COMP greater than
2007 Semtech Corp.
VO ⋅ (1 − D)
2 ⋅ L ⋅ fs
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SC4521
POWER MANAGEMENT
Application Information (Cont.)
Figure 2 shows the theoretical maximum load current
for the specific cases. In a real application, however, the
allowed maximum load current also depends on the layout
and the air cooling condition. Therefore, the maximum
load current may need to be degraded according to the
thermal situation of the application.
L=
Where:
fs = switching frequency,
δ = ratio of the peak to peak inductor current to the
output load current and
VO = output voltage.
The peak to peak inductor current is:
Iomax (A)
Maximum Load Current vs Input Voltage
L=10uH
2.900
2.880
2.860
2.840
2.820
2.800
2.780
2.760
2.740
2.720
2.700
VO ⋅ (VI − VO )
VI ⋅ f s ⋅ δ ⋅ IOMAX
I p − p = δ • I OMAX
After the required inductor value is selected, the proper
selection of the core material is based on the peak
inductor current and efficiency specifications. The core
must be able to handle the peak inductor current IPEAK
without saturation and produce low core loss during the
high frequency operation.
Vo=2.5V
Vo=3.3V
Vo=5V
IPEAK = IOMAX +
4
6
8
10
12
14
16
2
The power loss for the inductor includes its core loss and
copper loss. If possible, the winding resistance should
be minimized to reduce inductor’s copper loss. The core
must be able to handle the peak inductor current IPEAK
without saturation and produce low core loss during the
high frequency operation. The core loss can be found in
the manufacturer’s datasheet. The inductor’s copper loss
can be estimated as follows:
18
Vi (V)
Figure 2. Theoretical maximum load current curves
Inductor Selection
PCOPPER = I 2LRMS ⋅ R WINDING
The factors for selecting the inductor include its cost,
efficiency, size and EMI. For a typical SC4521 application,
the inductor selection is mainly based on its value,
saturation current and DC resistance. Increasing the
inductor value will decrease the ripple level of the output
voltage while the output transient response will be
degraded. Low value inductors offer small size and fast
transient responses while they allow large ripple currents,
poor efficiencies and require more output capacitance
for low output ripple. The inductor should be able to
handle the peak current without saturating and its copper
resistance in the winding should be as low as possible to
minimize its resistive power loss. A good trade-off among
its size, loss and cost is to set the inductor ripple current
to be within 15% to 30% of the maximum output current.
Where:
ILRMS is the RMS current in the inductor. This current can
be calculated as follows:
ILRMS = IOMAX ⋅ 1 +
1 2
⋅δ
12
Output Capacitor Selection
Basically there are two major factors to consider in
selecting the type and quantity of the output capacitors.
The first one is the required ESR (Equivalent Series
Resistance) which should be low enough to reduce the
output voltage deviation during load changes. The second
one is the required capacitance, which should be high
enough to hold up the output voltage. Before the SC4521
regulates the inductor current to a new value during a
The inductor value can be determined according to its
operating point under its continuous mode and the
switching frequency as follows:
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Ip − p
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SC4521
POWER MANAGEMENT
Application Information (Cont.)
load transient, the output capacitor delivers all the
additional current needed by the load. The ESR and ESL
of the output capacitor, the loop parasitic inductance
between the output capacitor and the load combined
with inductor ripple current are all major contributors to
the output voltage ripple. Surface mount ceramic
capacitors are recommended.
TW =
Where:
fs = the switching frequency and
Dmax = maximum duty ratio, 0.85 for the SC4521.
The required minimum capacitance for the boost
capacitor will be:
Input Capacitor Selection
C boost =
The input capacitor selection is based on its ripple current
level, required capacitance and voltage rating. This
capacitor must be able to provide the ripple current
drawn by the converter. For the continuous conduction
mode, the RMS value of the input capacitor current
ICIN(RMS) can be calculated from:
ICIN (RMS) = I OMAX ⋅
V
With fs = 600kHz, VD = 0.5V and IB = 0.045A, the required
minimum capacitance for the boost capacitor is:
I
This current gives the capacitor’s power loss through its
RCIN(ESR) as follows:
Cboost =
The input ripple voltage mainly depends on the input
capacitor’s ESR and its capacitance for a given load, input
voltage and output voltage. Assuming that the input
current of the converter is constant, the required input
capacitance for a given voltage ripple can be calculated
by:
D ⋅ (1 − D)
fs ⋅ ( ∆ VI − IOMAX ⋅ R CIN (ESR) )
Freewheeling Diode Selection
Where:
∆VI = the given input voltage ripple.
This diode conducts during the switch’s off-time. The diode
should have enough current capability for full load and
short circuit conditions without any thermal concerns.
Its maximum repetitive reverse block voltage has to be
higher than the input voltage of the SC4521. A low
forward conduction drop is also required to increase the
overall efficiency. The freewheeling diode should be
turned on and off fast with minimum reverse recovery
because the SC4521 is designed for high frequency
applications. SS23 Schottky rectifier is recommended
for certain applications. The average current of the diode,
ID_AVG can be calculated by:
Because the input capacitor is exposed to the large surge
current, attention is needed for the input capacitor. If
tantalum capacitors are used at the input side of the
converter, one needs to ensure that the RMS and surge
ratings are not exceeded. For generic tantalum
capacitors, it is suggested to derate their voltage ratings
at a ratio of about two to protect these input capacitors.
Boost Capacitor and its Supply Source Selection
The boost capacitor selection is based on its discharge
ripple voltage, worst case conduction time and boost
current. The worst case conduction time T w can be
estimated as follows:
2007 Semtech Corp.
IB 1
0.045
1
⋅ ⋅ Dmax =
⋅
⋅ 0.85 = 128nF
0.5 600k
VD fs
The internal driver of the switch requires a minimum 2.7V
to fully turn on that switch to reduce its conduction loss.
If the output voltage is less than 2.7V, the boost capacitor
can be connected to either the input side or an
independent supply with a decoupling capacitor. But the
Pin BST should not see a voltage higher than its maximum
rating.
PCIN = I2CIN (RMS) • R CIN(ESR)
C IN = IOMAX ⋅
IB
⋅ TW
VD
Where:
IB = the boost current and
VD= discharge ripple voltage.
VO ⋅ (VI − VO )
2
1
⋅ D max
fs
ID- AVG = Iomax ⋅ (I − D)
8
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SC4521
POWER MANAGEMENT
Application Information (Cont.)
Where:
RL – Load and
C – Output capacitor.
Thermal Considerations
There are three major power dissipation sources for the
SC4521. The internal switch conduction loss, its switching
loss due to the high frequency switching actions and the
base drive boost circuit loss. These losses can be
estimated as:
10
⋅ Io ⋅ D ⋅ (Vboost )
1000
2
IN
5
BST
1
Where:
IO = load current;
Ron = on-equivalent resistance of the switch;
VBOOST = input voltage or output based on the boost circuit
connection.
The junction temperature of the SC4521 can be
further determined by:
EN
SS
L1
3
COMP
6
7
C4
R3
D2
Figure 3. Compensation network provides 2 poles and
1 zero.
The freewheeling diode also contributes a significant
portion of the total converter loss. This loss should be
minimized to increase the converter efficiency by using
Schottky diodes with low forward drop (VF).
The compensation network gives the following
characteristics:
s
R2
ωZ
GCOMP (s) = ω1 ⋅
⋅ gm ⋅
s
R
+ R2
1
s ⋅ (1 +
)
ωP2
1+
Pdiode = VF ⋅ Io ⋅ (1 − D)
Loop Compensation Design
Where:
The SC4521 has an internal error amplifier and requires
a compensation network to connect between the COMP
pin and GND pin as shown in Figure 3. The compensation
network includes C4, C5 and R3. R1 and R2 are used to
program the output voltage according to:
R1
)
R2
ω1 =
1
C 4 + C5
ωZ =
1
R 3 ⋅ C4
ω P2 =
Assuming the power stage ESR (equivalent series
resistance) zero is an order of magnitude higher than
the closed loop bandwidth, which is typically one tenth of
the switching frequency, the power stage control to output
transfer function with the current loop closed (Ridley
model) for the SC4521 will be as follows:
2007 Semtech Corp.
R2
C5
θ JA is the thermal resistance from junction to ambient.
Its value is a function of the IC package, the application
layout and the air cooling system.
G VD (s) =
C
R1
TJ = TA + θ JA ⋅ Ptotal
VO = 0.8 • (1 +
Vout
SW
4
8
SC4521
FB
GND
2
Ptotal = Io ⋅ R on ⋅ D + 10.8 ⋅ 10 −3 ⋅ Io ⋅ VI +
The goal of the compensation design is to shape the loop
to have a high DC gain, high bandwidth, enough phase
margin, and high attenuation for high frequency noises.
Figure 3 gives a typical compensation network which
offers 2 poles and 1 zero to the power stage:
C 4 + C5
R 3 ⋅ C 4 ⋅ C5
The loop gain will be given by:
R
R2
1
T(s) = GCOMP (s) ⋅ G VD (s) = 3.655 ⋅ 10 ⋅ L ⋅
⋅
C4 R1 + R 2 s
1+
−3
4.3 ⋅ R L
s
1+
1
RL ⋅ C
(1 +
s
ωZ
s
s
) ⋅ (1 +
)
ωP1
ωP2
Where:
ωp1 =
9
1
RL ⋅ C
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SC4521
POWER MANAGEMENT
Application Information (Cont.)
One integrator is added at origin to increase the DC gain.
ωZ is used to cancel the power stage pole ωP1 so that the
loop gain has –20dB/dec rate when it reaches 0dB line.
ωP2 is placed at half switching frequency to reject high
frequency switching noises. Figure 4 gives the asymptotic
diagrams of the power stage with current loop closed
and its loop gain.
2. Start the PCB layout by placing the power components
first. Arrange the power circuit to achieve a clean
power flow route. Put all power connections on one
side of the PCB with wide copper filled areas if
possible.
3. The VIN bypass capacitor should be placed next to
the VIN and GND pins.
4. The trace connecting the feedback resistors to the
output should be short, direct and far away from any
noise sources such as switching node and switching
components.
5. Minimize the loop including input capacitor, the
SC4521 and freewheeling diode D2. This loop passes
high di/dt current. Make sure the trace width is wide
enough to reduce copper losses in this loop.
6. Maximize the trace width of the loop connecting the
inductor, freewheeling diode D 2 and the output
capacitor.
7. Connect the ground of the feedback divider and the
compensation components directly to the GND pin
of the SC4521 by using a separate ground trace.
8. Connect Pin 4 to a large copper area to remove the
IC heat and increase the power capability of the
SC4521. A few feedthrough holes are required to
connect this large copper area to a ground plane to
further improve the thermal environment of the
SC4521. The traces attached to other pins should
be as wide as possible for the same purpose.
Loop gain T(s)
ωp1
Power stage
ωC
ωP2
ωZ
Figure 4. Asymptotic diagrams of power stage with
current loop closed and its loop gain.
The design guidelines for the SC4521 applications are
as following:
1. Set the loop gain crossover corner frequency ωC for
given switching corner frequency ωC = 2πfC
2. Place an integrator at the origin to increase DC and
low frequency gains.
3. Select ωZ such that it is placed at ωP1 to obtain a
-20dB/dec rate to go across the 0dB line.
4. Place a high frequency compensator pole
ωP2 (ωP2 = πfs) to get the maximum attenuation of
the switching ripple and high frequency noise with
the adequate phase lag at ωC.
Layout Guidelines:
In order to achieve optimal electrical and thermal
performance for high frequency converters, special
attention must be paid to the PCB layouts. The goal of
layout optimization is to identify the high di/dt loops and
minimize them. The following guidelines should be used
to ensure proper operation of the converters.
1. A ground plane is suggested to minimize switching
noises and trace losses and maximize heat
transferring.
2007 Semtech Corp.
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SC4521
POWER MANAGEMENT
Application Information (Cont.)
Design Example 1: 5V to 1V at 2A
D1
1
C1
0.22u
C3
10u
5
8
Css
100n
IN
L1
BST
0
2
EN
SS
Vo=1V @2A
3
SW
3.9uH
6
FB
GND
R0
4
VI = 5V
R1
2.49k
Co
470u
7
COMP
SC4521
C4
18n
C5
560p
R3
20k
R2
10k
D2
Note: The bottom pad needs a big copper area to remove the heat.
Bill of Materials
Item
Qty
Reference
Value
Part No./Manufacturer
1
1
C1
0.22uF, 25V, 0805, X7R
Vishay: VJ0805Y224KXX
2
1
Co
470uF, 10V, ZA
Rubicon
3
1
C3
10uF
TDK: C3216OJ106MT
4
1
C4
18nF, 0805, X7R, 25V
Vishay
5
1
C5
560pF, 50V, 0805
Vishay
6
1
D1
1N4148SW, SOD323
7
1
D2
E C 30LA 02
Nihon Inter Electronics Corp.
8
1
L1
3.9uH
Sumida: RCR875DNP-3R9L
9
1
R0
0, 0805
10
1
R1
2.49k, 1%, 0805
11
1
R2
10k, 1%, 0805
12
1
R3
20k, 1%, 0805
13
-
R4
not used, 0805
14
1
C ss
100nF
15
1
U1
S C 4521
SMTZONE
Semtech
Unless specified, all resistors have 1% precision with 0805 package.
Resistors are +/-1% and all capacitors are +/-20%
2007 Semtech Corp.
11
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SC4521
POWER MANAGEMENT
Application Information (Cont.)
Design Example 2: 6.2V to 1.5V at 1.5A
D1
1
C1
0.22u
C3
10u
5
8
Css
100n
IN
L1
BST
0
2
EN
SS
Vo=1.5V
3
SW
4.7uH
6
FB
GND
R0
4
VI = 6.2V
COMP
R1
8.66k
Co
100u
7
SC4521
C4
18n
C5
560p
R3
4.87k
R2
10k
D2
Note: The bottom pad needs a big copper area to remove the heat.
Bill of Materials
Item
Qty
Reference
Value
Part No./Manufacturer
1
1
C1
0.22uF, 25V, 0805, X7R
Vishay: VJ0805Y224KXX
2
1
Co
100uF
Sanyo
3
1
C3
10uF
TDK: C3216OJ106MT
4
1
C4
18nF, 0805, X7R, 25V
Vishay
5
1
C5
560pF, 50V, 0805
Vishay
6
1
D1
1N4148SW, SOD323
7
1
D2
MBRA210LT3
ON
8
1
L1
4.7uH
Toko: 919AS-4R7
9
1
R0
0, 0805
Vishay
10
1
R1
8.66k, 1%, 0805
Vishay
11
1
R2
10k, 1%, 0805
Vishay
12
1
R3
4.87k, 0805
Vishay
13
-
R4
not used, 0805
14
1
C ss
100nF
15
1
U1
S C 4521
Semtech
Unless specified, all resistors have 1% precision with 0805 package.
Resistors are +/-1% and all capacitors are +/-20%
2007 Semtech Corp.
12
www.semtech.com
SC4521
POWER MANAGEMENT
Application Information (Cont.)
Design Example 3: 13V ~ 21V to 3.3V at 1A
D3
1
C1
0.22u
0
C3
4.7u
Rss
200k
5
8
Css
330n
IN
L1
BST
2
SS
Vo=3.3V
3
SW
EN
10uH
6
FB
GND
R0
4
VI
R1
24.9k
C2
10u
7
COMP
SC4521
R2
8.25k
C4
18n
C5
560p
R3
3.83k
D2
Note: The bottom pad needs a big copper area to remove the heat.
Bill of Materials
Item
Qty
Reference
Value
Part No./Manufacturer
1
1
C1
0.22uF, 25V, 0805, X7R
Vishay: VJ0805Y224KXX
2
1
C2
10uF
Taiyo-Yuden:
EDK316BJ106MF-T
3
1
C3
4.7uF, 1206, 25V, X5R
Panasonic
4
1
C4
18nF, 0805, X7R, 25V
Vishay
5
1
C5
560pF, 50V, 0805
Vishay
6
1
D2
7
1
D3
1N4148WS, SOD323
8
1
L1
10uH
9
1
R0
0, 0805
10
1
R1
24.9k, 1%, 0805
SMTZONE
11
1
R2
8.25k, 1%, 0805
SMTZONE
12
1
R3
3.83k, 1%, 0805
SMTZONE
13
-
Rss
2 0 0 k, 0 8 0 5
14
1
C ss
330nF, 0805
15
1
U1
S C 4521
Nihon-International: EC31QS04
Sumida:
CDRH6D38NP-100NC
Semtech
Unless specified, all resistors have 1% precision with 0805 package.
Resistors are +/-1% and all capacitors are +/-20%
2007 Semtech Corp.
13
www.semtech.com
SC4521
POWER MANAGEMENT
Application Information (Cont.)
Design Example 4: 13V ~ 21V to 5V at 1.5A
D3
1
C1
0.22u
2
0
C3
4.7u
Rss
200k
5
8
L1
EN
SS
Vo=5V
3
SW
10uH
6
FB
4
Css
470n
IN
BST
R0
GND
VI
R1
51.1k
C2
10u
7
COMP
SC4521
R2
10k
C4
18n
C5
560p
R3
4.87k
D2
Note: The bottom pad needs a big copper area to remove the heat.
Bill of Materials
Item
Qty
Reference
Value
Part No./Manufacturer
1
1
C1
0.22uF, 25V, 0805, X7R
Vishay: VJ0805Y224KXX
2
1
C2
10uF
Taiyo-Yuden:
EDK316BJ106MF-T
3
1
C3
4.7uF, 1206, 25V, X5R
Panasonic
4
1
C4
18nF, 0805, X7R, 25V
Vishay
5
1
C5
560pF, 50V, 0805
Vishay
6
1
D2
7
1
D3
1N4148WS, SOD323
8
1
L1
10uH
9
1
R0
0, 0805
10
1
R1
51.1k, 1%, 0805
SMTZONE
11
1
R2
10k, 1%, 0805
SMTZONE
12
1
R3
4.87k, 1%, 0805
SMTZONE
13
-
Rss
2 0 0 k, 0 8 0 5
14
1
C ss
470nF, 0805
15
1
U1
S C 4521
Nihon-International: EC31QS04
Sumida:
CDRH6D38NP-100NC
Semtech
Unless specified, all resistors have 1% precision with 0805 package.
Resistors are +/-1% and all capacitors are +/-20%
2007 Semtech Corp.
14
www.semtech.com
SC4521
POWER MANAGEMENT
Application Information (Cont.)
(PCB - TOP)
(PCB - BOTTOM)
2007 Semtech Corp.
15
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SC4521
POWER MANAGEMENT
Application Information (Cont.)
(Componet Side - TOP)
(Componet Side - TOP)
2007 Semtech Corp.
16
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SC4521
POWER MANAGEMENT
Outline Drawing - SOIC-8L EDP
A
D
e
N
DIM
2X E/2
E1 E
1
2
ccc C
2X N/2 TIPS
e/2
B
D
aaa C
SEATING
PLANE
A2 A
C
A1
bxN
bbb
DIMENSIONS
INCHES
MILLIMETERS
MIN NOM MAX MIN NOM MAX
A
A1
A2
b
c
D
E1
E
e
F
H
h
L
L1
N
01
aaa
bbb
ccc
.069
.053
.005
.000
.065
.049
.012
.020
.010
.007
.189 .193 .197
.150 .154 .157
.236 BSC
.050 BSC
.116 .120 .130
.085 .095 .099
.010
.020
.016 .028 .041
(.041)
8
0°
8°
.004
.010
.008
C A-B D
1.75
1.35
0.13
0.00
1.65
1.25
0.31
0.51
0.25
0.17
4.80 4.90 5.00
3.80 3.90 4.00
6.00 BSC
1.27 BSC
2.95 3.05 3.30
2.15 2.41 2.51
0.25
0.50
0.40 0.72 1.04
(1.05)
8
8°
0°
0.10
0.25
0.20
h
F
EXPOSED PAD
h
H
H
c
GAGE
PLANE
0.25
SEE DETAIL
L
(L1)
A
DETAIL
01
A
SIDE VIEW
NOTES:
1.
CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
2. DATUMS -A- AND -B- TO BE DETERMINED AT DATUM PLANE -H3. DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS
OR GATE BURRS.
4. REFERENCE JEDEC STD MS-012, VARIATION BA.
2007 Semtech Corp.
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SC4521
POWER MANAGEMENT
Land Pattern - SOIC-8L-EDP
E
SOLDER MASK
D
DIM
(C)
G
F
C
D
E
F
G
P
X
Y
Z
Z
Y
THERMAL VIA
Ø 0.36mm
P
X
DIMENSIONS
INCHES
MILLIMETERS
(.205)
.134
.201
.101
.118
.050
.024
.087
.291
(5.20)
3.40
5.10
2.56
3.00
1.27
0.60
2.20
7.40
NOTES:
1.
THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY.
CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR
COMPANY'S MANUFACTURING GUIDELINES ARE MET.
2. REFERENCE IPC-SM-782A, RLP NO. 300A.
3.
THERMAL VIAS IN THE LAND PATTERN OF THE EXPOSED PAD
SHALL BE CONNECTED TO A SYSTEM GROUND PLANE.
FAILURE TO DO SO MAY COMPROMISE THE THERMAL AND/OR
FUNCTIONAL PERFORMANCE OF THE DEVICE.
Contact Information
Semtech Corporation
Power Management Products Division
200 Flynn Road, Camarillo, CA 93012
Phone: (805)498-2111 FAX (805)498-3804
2007 Semtech Corp.
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