SC2603ASKTRT [SEMTECH]
Simple PWM Boost Converter In Small SOT23-6 Package;
| 型号： | SC2603ASKTRT |
| 厂家： | 
SEMTECH CORPORATION |
| 描述： | Simple PWM Boost Converter In Small SOT23-6 Package |
| 文件： | 总9页 (文件大小：461K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
SC2603A
Simple PWM Boost Converter
In Small SOT23-6 Package
POWER MANAGEMENT
Features
Description
The SC2603A is a versatile, low-cost, voltage-mode PWM
controller designed for DC/DC power supply applications.
A simple, fixed-voltage boost regulator can be implemented
using the SC2603A with a minimum of external compo-
nents. The small device footprint allows for compact circuit
design.
Low cost / small size
Input voltage range: 5V to 30V
ꢀ200kHz switching frequency
Up to 95% efficiency
ꢀꢀ% reference voltage accuracy
ꢀTypical 800mA PWM gate drive capability
Internal compensation
SC2603A features include a temperature compensated
voltage reference, triangle wave oscillator, current limit
comparator, frequency shift over-current protection, and
an internally compensated error amplifier. Pulse by pulse
current limiting is implemented by sensing the differential
voltage across an external resistor, or an appropriately
sized PC board trace.
Over current protection
SOT23-6 package is fully WEEE and RoHS compliant
Applications
Portable Devices
ꢀFlat Panel TV
ꢀTV Set Top Box
ꢀAuxiliary Supplies
ꢀPeripheral Card Supplies
Industrial Power Supply
High Density DC/DC Conversion
The SC2603A operates at a fixed frequency of 200kHz,
providing an optimum compromise between efficiency,
external component size, and cost.
Typical Application Circuit
L1
D1
VOUT
VIN
1
2
R1
+
+
C1
C2
Q1
R6
C3
D2
R2
R4
U1
Optional
5
3
1
4
6
2
VIN
GATE
CS
Enable
R5
EN/SS
FB
GND
C4
C5
SC2603A
Figure ꢀ: ꢀ2V to 25V/ꢀA Boost Conveter
Revision: May 8, 2007
ꢀ
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SC2603A
POWER MANAGEMENT
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. Exposure to Absolute Maximum rated conditions for extended periods of time may affect device
reliability.
Parameter
Symbol
Maximum
Units
Input Voltage
VIN to GND
VGATE
-0.3 to 20
-0.3 to 20
-0.3 to 7
-0.3 to 7
V
V
V
V
GATE Pin Voltage
EN/SS Pin Voltage
FB Pin Voltage
VEN/SS
VFB
Thermal Resistance Junction to Ambient(1)
Thermal Resistance Junction to Case
Maximum Junction Temperature
Storage Temperature Range
165
102
°C/W
°C/W
°C
θ JA
θ JC
TJ
150
-45 to +150
°C
TSTG
Lead Temperature (Soldering)10 sec
ESD Rating (Human Body Model)
300
2
°C
kV
TLEAD
ESD
Note:
(1) Mounting pad has to be larger than one square inch on two sided printed circuit board with minimum 1 ounce copper
Electrical Characteristics
Unless specified: VIN = ꢀ2V, VO = 25V; TA = TJ = -40°C to ꢀ25°C
Parameter
General
Symbols
Conditions
Min
Typ
Max
Units
VIN Supply Voltage
VIN UVLO Threshold
VIN UVLO Hysteresis
VIN Supply Current
VIN Shutdown Current
Error Amplifier
VIN
4.5
16
V
VUVLO
VHYS
VIN ramping up
4.2
400
6.0
5.0
4.5
V
mV
mA
mA
Current into VIN pin during switching
EN/SS=Low
9.0
6.0
Reference Voltage
Feedback Bias Current
Error Amplifier Gain(1)
Oscillator
VFB
IFB
1.225
1.250
2.0
1.275
8.0
V
VIN = 12V, VFB = VEN/SS
µA
V/V
105
Oscillator Frequency
Oscillator Frequency Shift
Maximum Duty Cycle
Internal Ramp Peak
Internal Ramp Valley
2007 Semtech Corp.
TA = 25 °C
190
90
200
50
210
kHz
kHz
%
VFB < VREF /2
95
VR_PEAK
1.4
0.4
V
VR_VALLEY
V
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SC2603A
POWER MANAGEMENT
Electrical Characteristics (Cont.)
Parameter
Symbols
Conditions
Min
Typ
Max
Units
Regulation
Load Regulation
IO = 0.1A to 1A
0.3
0.5
0.5
1.0
%
%
Line Regulation
VIN = 5V to 15V, Io = 0.1A
PWM Gate Drive
GATE Source Current
GATE Sink Current
Enable and Soft Start
Soft Start Charge Current
VIN = 12V, CGATE = 10nF
VIN = 12V, CGATE = 10nF
0.5
0.5
0.8
0.8
1.1
1.1
A
A
ISS
60
µA
Pull down below this level to
disable PWM Switch gate
Enable/Soft Start Threshold
0.09
0.12
V
Switch Current Limit
Current Limit Threshold
CS
65
73
80
mV
Note:
(1) Guaranteed by design
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2007 Semtech Corp.
3
SC2603A
POWER MANAGEMENT
Ordering Information
Part Number
Pin Configurations
TOP VIEW
Package
SC2603ASKTRT(1,2)
SOT23-6
FB
GND
CS
1
2
3
6
5
4
SC2603AEVB
Evaluation Board
VIN
EN/SS
GATE
Notes:
(1) Only available in tape and reel packaging. A reel
contains 3000 devices.
(2) Lead free product. This product is fully WEEE
and RoHS compliant.
(6 Pin SOT-23)
Pin Descriptions
Pin
Pin Name
Pin Function
1
2
3
4
5
6
FB
GND
EN/SS
GATE
VIN
Error amplifier inverted input
Device ground
Enable / Soft Start Pin
PWM gate driver output
Device input voltage
Current Sense input
CS
Block Diagram
OSCILLATOR
VIN
S
PWM
Q
FB
GATE
R
GND
25K
Current
Limit
CS
EN/SS
1.25V
REF
70mV
UV
VIN
UVLO
1.25V
REF
Figure 2: SC2603A Function Diagram
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SC2603A
POWER MANAGEMENT
Applications Information
Maximum Duty Cycle
Theory of Operation
The maximum duty cycle, D defines the upper limit of
power conversion ratio
The SC2603A is a versatile, low-cost, voltage-mode PWM
controller designed for DC/DC power supply applications.
In normal condition, the SC2603A operates at a fixed
200kHz. One exception is that when the FB pin voltage
drops to one half, the frequency will be shifted to one
fourth of 200kHz.
max
VOUT
VIN
ꢀ
=
ꢀ − DMAX
SC2603A features include a temperature compensated
voltage reference, triangle wave oscillator, current limit
comparator, frequency shift over-current protection, and
an internally compensated error amplifier. Pulse by pulse
current limiting is implemented by sensing the differential
voltage across an external resistor, or an appropriately
sized PC board trace.
Clamping Diode D2 at Vin Pin
Since the Vin pin of the SC2603A is rated at 20V, when
the supply voltage is higher than ꢀ6V, a Zener diode D2
is required to limit the SC2603A supply voltage, as shown
in Fig.1. The clamping voltage of D2 has to be not higher
than ꢀ5V.
Setting the Output Voltage
Over Current Protection (OCP)
As shown in Fig.1, an external resistive divider R2 and R4
with its center tap tied to the FB pin sets the output volt-
age.
The over-current protection is implemented by a sensing
resistor and an internal current-limit comparator with a
threshold of 70mV. In each switching cycle, if the switching
current through the sensing resistor causing the voltage at
the CS pin reaches 70mV, the SC2603A will immediately
turn the gate pulse off to limit the current through the
power switch.
VOUT
4
R2 = R
−ꢀ
ꢀ.25V
Soft-Start
The figure below shows the current waveforms run into
over-current protection. At t1, the input current Iin begins
to increase as the load Iout builds up until it hits the OCP
threshold at t2. At t2, Vout begins to drop as Iout starts
increasing toward t3 while Vin and Iin remain the same.
At t3, there two events are happening. ꢀ) Vout is at half of
its regulating voltage. At this point, the internal oscillator
runs into frequency shift mode and shifts the frequency to
one fourth of the operating frequency. 2) The diode starts
conducting current without limit causing Vin to fall due to
supply current limit. Finally, Vin and Vout both drops to zero
and Iin becomes the input supply current limit.
Soft-start prevents a DC-DC converter from drawing exces-
sive current from the power source during start up. If the
soft-start time is made sufficiently long, then the output will
enter regulation without overshoot. An external capacitor
is connected from the EN/SS pin to the ground. After the
part’s input voltage surpasses the UVLO, the EN/SS pin is
allowed to charge its capacitor with 60µA. When ꢀ00mV
is reached at the EN/SS pin, the internal comp node is at
0.4V. The SC2603A will start switching, and the converter
output comes into regulation. Because the FB pin voltage
follows EN/SS pin voltage, finally, the EN/SS pin voltage will
be clamped at 1.25V same as the reference voltage.
A RC filter at the CS pin is necessary to filter out noise to
ensure accurate sensing.
Under Voltage Lockout
The value of the sensing resistor can be calculated by the
following equation:
The under voltage lockout circuit of the SC2603A assures
that the Gate output remains in the off state whenever the
supply voltage drops below set parameters. Lockout occurs
if Vin falls below 3.8V. Normal operation resumes once Vin
rises above 4.2V.
Rs = 70mV/Ipeak
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SC2603A
POWER MANAGEMENT
Applications Information (Cont.)
in more reliable gate switching signals.
where Ipeak is the input peak current through the power
MOSFET.
3) The connection between the junction of Q1, D1 and the
output capacitor should be a wide trace or copper region.
It should be as short as practical. Since this connection
has fast voltage transitions, keeping this connection short
will minimize EMI.
Normal
Loading
Supply Current Limiting
SS
OCP
4) The Output Capacitor(s) (Cout) should be located as
close to the load as possible, fast transient load currents
are supplied by Cout only, and connections between Cout
and the load must be short, wide copper areas to minimize
inductance and resistance.
IIN
IOUT
5) The SC2603A is best placed over an isolated ground
plane area. The soft-start capacitor, the Vin decoupling ca-
pacitor, and the current sensing filter capacitor should also
connected to this ground pad area. This isolated ground
area should be connected to the main ground by a trace
that runs from the GND pin to the ground side of the output
capacitor. If this is not possible, the GND pin may be con-
nected to the ground path between the Output Capacitor
and the Cin, Q1, D1 loop. Under no circumstances should
GND be returned to a ground inside the Cin, Q1, D1 loop.
VOUT
VIN
t0
t2
t3
t1
t4
Figure 3. Current Waveforms
Layout Guidelines
6) Input voltage of the SC2603A should be supplied from
the power rail through a 2.2~10Ω resistor, the Vin pin
should be decoupled directly to GND by a 0.1µF~1µF
ceramic capacitor, trace lengths should be as short as
possible.
Careful attentions to layout requirements are necessary
for successful implementation of the SC2603A PWM con-
troller. High currents switching at 200kHz are present in
the application and their effect on ground plane voltage
differentials must be understood and minimized.
7) An RC low pass filter is required to filter out leading
edge current spikes on the current sensing resistor. The
filter capacitor needs to be very close to the CS and GND
to reduce noise pickup.
1) The high power parts of the circuit should be laid out
first. A ground plane should be used. The number and
position of ground plane interruptions should be such as
to not unnecessarily compromise ground plane integrity.
Isolated or semi-isolated areas of the ground plane may
be deliberately introduced to constrain ground currents to
particular areas, for example the input capacitor and bot-
tom Schottky ground.
2) The loop formed by the output Capacitor(s) (Cout), the
FET (Q1), the current sensing resistor, and the Schottky (D1)
must be kept as small as possible, as shown on the layout
diagram in Fig.4. This loop contains all the high current, fast
transition switching. Connections should be as wide and
as short as possible to minimize loop inductance. Minimiz-
ing this loop area will reduce EMI, lower ground injection
currents, resulting in electrically “cleaner” grounds for the
rest of the system and minimize source ringing, resulting
2007 Semtech Corp.
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SC2603A
POWER MANAGEMENT
Applications Information (Cont.)
Layout diagram for the SC2603A
Vout
12VIN
Ra
D1
L1
Cin
+
2.2
Q1
SC2603A
Cout
Rb
1
4
2
5
FB
VIN
3
GATE
GND
EN/SS
CS
0.1uF
0.1uF
Rs
6
Note: Heavy lines indicate the critical loop carrying high pulsating current.
The inductance of the loop needs to be minimized.
Figure 4: SC2603A Layout Diagram
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SC2603A
POWER MANAGEMENT
Applications Information (Cont.)
Typical application schematic with 12V input and 24V/1A output
D1
24V/1A OUTPUT
12VINPUT
L1
1
2
33uH
CMSH2-40M
C11
C1
220uF
C10
1uF
1uF
C2
330uF
+
+
R1
2R2
Q1
IRF7821
R2
226k
Rc
2.3k
U1
R5
1k
1
2
3
6
5
4
FB
CS
VIN
R4
12.4k
GND
EN/SS
Cc
C5
120pF
R6
20m
GATE
56nF
C3
C4
0.1uF
1uF
SC2603A
Bill of materials
Item Quantity Reference
Part
Vendor
1
2
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
C1
220uF/16V
330uF/35V
1uF/16V
0.1uF
Panasonic
Nichicon, VR
Vishay
C2
3
C3,C10
C4
4
Vishay
5
C5
120pF
Vishay
6
C11
Cc
1uF/50V
56nF
Vishay
7
Vishay
8
9
D1
L1
CMSH2-40M
33uH/5.1A (HC8-330)
Central Semi
Coiltronics
IR
10
11
12
13
14
15
16
17
Q1
R1
IRF7821
2R2
Vishay
R2
226k
Vishay
R4
12.4k
1k
Vishay
R5
Vishay
R6
20m
Vishay
Rc
2.3k
Vishay
U1
SC2603A
Semtech
2007 Semtech Corp.
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8
SC2603A
POWER MANAGEMENT
Outline Drawing - SOT23-6
DIMENSIONS
INCHES MILLIMETERS
A
DIM
MIN NOM MAX MIN NOM MAX
-
-
-
-
A
.057 0.90
.006 0.00
1.45
0.15
.035
A1 .000
e1
D
E
A2 .035 .045 .051 .90 1.15 1.30
-
-
-
-
b
c
.010
.003
.020 0.25
.009 0.08
0.50
0.22
N
2X E/2
EI
D
.110 .114 .122 2.80 2.90 3.10
E1 .060 .063 .069 1.50 1.60 1.75
1
2
E
e
e1
L
.110 BSC
.037 BSC
.075 BSC
2.80 BSC
0.95 BSC
1.90 BSC
ccc
C
2X N/2 TIPS
.012 .018 .024 0.30 0.45 0.60
e
(.024)
6
(0.60)
6
L1
N
B
-
-
01
aaa
bbb
ccc
0°
10°
0°
10°
.004
.008
.008
0.10
0.20
0.20
D
aaa C
A2
A
SEATING
PLANE
H
A1
C
c
bxN
bbb
GAGE
PLANE
C
A-B D
0.25
L
01
(L1)
DETAIL
A
SEE DETAIL
A
SIDE VIEW
NOTES:
1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
2. DATUMS -A- AND -B- TO BE DETERMINED AT DATUM PLANE -H-
3. DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS
OR GATE BURRS.
Land Pattern - SOT23-6
X
DIMENSIONS
DIM
INCHES
(.098)
.055
.037
.024
MILLIMETERS
(2.50)
1.40
0.95
0.60
1.10
3.60
C
G
P
X
Y
Z
(C)
G
Z
Y
.043
.141
P
NOTES:
1. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY.
CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR
COMPANY'S MANUFACTURING GUIDELINES ARE MET.
Contact Information
Semtech Corporation
Power Management Products Division
200 Flynn Road, Camarillo, CA ꢁ30ꢀ2
Phone: (805)4ꢁ8-2ꢀꢀꢀ FAX (805)4ꢁ8-3804
www.semtech.com
2007 Semtech Corp.
ꢁ
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