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SC2603
Simple PWM Boost Controller
POWER MANAGEMENT Description
The SC2603 is a versatile, low-cost, voltage-mode PWM controller designed for 16V input DC/DC power supply applications. A simple, fixed-voltage boost regulator can be implemented using the SC2603 with a minimum of external components. The small device footprint allows for compact circuit design. SC2603 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. The SC2603 operates at a fixed frequency of 200kHz, providing an optimum compromise between efficiency, external component size, and cost.
Features
Low cost / small size Switch mode efficiency up to 95% 1% reference voltage accuracy Over-current protection 800mA output drive 5V to 16V input power source No need for external compensation network SOT23-6 is fully WEEE and RoHS compliant
Applications
Portable Devices Flat Panel TV TV Set Top Box Auxiliary Supplies Peripheral Card Supplies Industrial Power Supplies High Density DC/DC Conversion
Typical Application Circuit
D1
L1
VIN
R1
VOUT
C1
R2
C2
Q1
C3
D2 optional
5
U2
VIN
Gate 4
GND
R3
Enable
(open collector) Open Drain with < 100 pull down impedance
3
1
C4
EN/SS CS
FB
GND
6
2
C5
R4
R5
SC2603
Revision: Nov 14, 2006
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SC2603
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 Storage Temperature Range Maximum Junction Temperature Lead Temperature (Soldering) 10 Sec. Thermal Resistance, Junction to Ambient(1) Thermal Resistance, Junction to Case Electrical Surge Discharge(2)
Symbol VIN to GND TSTG TJ TLEAD JA JC ESD
Maximum -0.3 to 20 -45 to +150 150 300 165 102 2
Units V C C C C/W C/W KV
Note: (1) Mounting pad has to be larger than one square inch on two sided printed circuit board with minimum 1 ounce copper (2) Human model.
Electrical Characteristics
VIN= 12V; VO = 25V; TA = TJ = -40C to 125C unless otherwise specified.
Parameter Reference Feedback Bi as C urrent Qui escent C urrent Load Regulati on Li ne Regulati on C urrent Li mi t Threshold Osci llator Frequency Osci llator Frequency Shi ft Max D uty C ycle UVLO Threshold UVLO Hysteresi s D ri ver Source C urrent D ri ver Si nk C urrent Soft Start C harge C urrent Internal Ramp Peak Internal Ramp Valley Enable Threshold
Symbols VREF IFB IQ
C onditions
Min 1.225
Typ 1.250 2.0 5.0 0.5 1.4
Max 1.275 8.0 8.0 1.0 2 78 210
U nits V A mA % % mV kHz kHz %
VFB = VEN/SS, VIN = 12V C urrent i nto VIN pi n VO=25V ; IO = 0.1A to 1A VIN=5V to 15V ; VO=25V ; IO = 100mA CS TA = 25OC VFB < VREF/2 90 68 190
73 200 50 95 4.2 400
VUVLO
VIN rampi ng up
4.5
V mV
ISOURCE ISINK ISS VR_PEAK VR_VALLEY VTH_EN
VIN = 12V, C GATE = 10nF VIN = 12V, C GATE = 10nF
0.5 0.5
0.8 0.8 60 1.4 0.4
1.1 1.1
A A A V V V
Pull down below thi s level to di sable the output
0.09
0.12
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SC2603
POWER MANAGEMENT Pin Configuration
Top View
FB GND EN/SS 1 2 3 6 5 4 CS VIN GATE
Ordering Information
P art N umbers S C 2603S K TRT (1)(2) S C 2603E V B P ackag e S OT23-6
SOT23-6
Note: (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
Pin Descriptions
Pin # 1 2 3 4 5 6 Pin Name FB GND EN/SS Gate VIN CS Pin Function Error amplifier input (-). Device ground. Enable/Soft Start Pin. Gate driver output. Device Input Voltage. Current Sense Input .
Block Diagram
OSCILLATOR
VIN
PWM S Q R
FB
Gate GND
25K Current Limit
CS
EN/SS
1.25V REF UV 70mV
VIN 1.25V REF
UVLO
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SC2603
POWER MANAGEMENT Theory of Operation
The SC2603 is a versatile, low-cost, voltage-mode PWM controller designed for DC/DC power supply applications. In normal condition, the SC2603 operats at a fixed 200KHz. One exception is that when the FB pin voltage drops to one half, the frequency will be shifted to one fouth of 200KHz. SC2603 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.
Application Information
Soft-Start Soft-start prevents a DC-DC converter from drawing excessive 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 60A. When 100mV is reached at the EN/SS pin, the internal comp node is at 0.4V. The SC2603 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 refernece voltage. Setting the Output Voltage An external resistive divider R1 and R2 with its center tap tied to the FB pin sets the output voltage.
VOUT
V R 1 = R 2 OUT - 1 1 . 25
R1 1
SC2603
FB
R2
Under Voltage Lockout The under voltage lockout circuit of the SC2603 assures that the gate driver 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.
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SC2603
POWER MANAGEMENT Application Information
Over Current Protection The over-current protection is implemented by a sensing resistor and an internal current-limit comparator with a threshold of 70mV. If the switching current through the sensing resistor causing voltage to drop at the CS pin reachs 70mV, the SC2603 will immediately turn the gate pulse off to limit the current through the power switch. The figure below shows over-current waveforms. 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. 1) 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. A RC filter at the CS pin is necessary to filter out noise to ensure accurate sensing. The value of the sensing resistor can be caculated by the following equation:
R S = 70 mV / I PEAK
Where IPEAK is the input peak current through the power MOSFET.
IIN
IOUT
VOUT
VIN
t0 t1 t2 t3 t4
Over Current Waveforms
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SC2603
POWER MANAGEMENT Applications Information
Layout Guidelines Careful attention to layout requirements are necessary for successful implementation of the SC2603 PWM controller. High currents switching at 200kHz are present in the application and their effect on ground plane voltage differentials must be understood and minimized. 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 bottom 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. This loop contains all the high current, fast transition switching. Connections should be as wide and as short as possible to minimize loop inductance. Minimizing 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 in more reliable gate switching signals. 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. 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. 5) The SC2603 is best placed over an isolated ground plane area. The soft-start capacitor, the VIN decoupling capacitor, 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 connected 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. 6) Input voltage of the SC2603 should be supplied from the power rail through a 2.2~10 resistor, the VIN pin should be decoupled directly to GND by a 0.1F~1f ceramic capacitor, trace lengths should be as short as possible. 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.
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SC2603
POWER MANAGEMENT Applications Information (Cont.)
Layout diagram for the SC2603
Vout
12VIN
Ra
20uH
D1
Cin
2.2 5 3 0.1uF 0.1uF SC2603 VIN EN/SS CS FB Gate GND 1 4 Rs Rb Q1 +
Cout
6
2
Heavy lines indicate the critical loop carrying high pulsating current. The inductance of this loop needs to be minimized.
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SC2603
POWER MANAGEMENT Applications Circuit
12V to 25V @ 1A boost converter
L1 VIN = 12V R1 2.2 C1 470u 18uH D1 VOUT=25V
3A, 40V
R2 34K C2 C11 1u 330u/35V R4
C3 1u 5 Enable (open drain) 3 1 C4 0.1u U2 VIN Gate 4 6 2 C5 SC2603 120p R5 1K
Q1 AO4442
1.78K
EN/SS CS FB GND
Open Drain with < 100 pull down impedance
R6 20m
Bill of Material
Item 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Quantity 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Reference C1 C2 C3 C4 C5 C11 D1 L1 Q1 R1 R2 R3 R4 R5 R6 U1 Part 470u/Alum 330u/Alum 1uF 0.1u 120p 1u 1N5819 18uH AO4442 2.2 34K 0 1.78K 1K 20m SC2603 SOT23-6 SEMTECH 603 603 603 603 603 COOPER Alpha & Omega 603 603 603 805 footprint Vendor SANYO SANYO
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SC2603
POWER MANAGEMENT Typical Characteristics
Error Amplifier: Gain and Phase
40 35
26
Load Regulation (VIN = 12V, VO = 25V)
180
30 25
135
25.5
15 Gain 10 5 0 -5 -10 100.0E+0 -45 10.0E+6 0 Phase 45
Phase (deg)
Gain (dB)
20
90
Output Voltage - (V)
25
24.5
24
23.5
23 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
Output Current - (A)
1.0E+3
10.0E+3
100.0E+3
1.0E+6
Frequency (Hz)
Efficiency (VIN = 12V, VO = 25V)
Line Regulation (VO = 25V, IO = 1A)
26.000
98 96 94
25.500
Output Voltage - (V)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1
Efficiency - (%)
92 90 88 86 84 82 80
25.000
24.500
24.000
23.500
23.000 4 6 8 10 12 14 16
Output Current - (A)
Input V oltage - (V )
OCP (VIN = 12V, VO = 25V)
Frequency Shift (VFB vs. FSW)
25.6
25.4
Output Voltage - (A)
25.2
25
24.8
24.6
24.4
24.2 0 0.5 1 1.5 2 2.5 3
Output Current - (A)
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SC2603
POWER MANAGEMENT Typical Characteristics
Reference Voltage vs Temperature UVLO Hysteresis vs Temperature
1.26
0 .5 5 0 .5
REFERENCE VOLTAGE (V)
1.255 1.25 1.245 1.24 1.235 1.23 1.225
UVLO HYSTERESIS (V)
150
VIN=12V
0 .4 5 0 .4 0 .3 5 0 .3 0 .2 5 0 .2
VIN=5V
1.22 -50
-25
0
25
50
75
100
125
0 .1 5 -5 0 0 50 100 150
TEMPERATURE (oC)
T E M P E R A T U R E (OC )
Oscillator Frequency vs Temperature
Current Limit Threshold vs Temperature
CURRENT LIMIT THRESHOLD (mV)
210
75
OSCILLATOR FREQUENCY (kHz)
205 200 195 190 185 180 -5 0 -2 5 0 25 50 75 100 125 150
74
73
72
71
70
69
68
-50
-25
0
25
50
75
100
125
150
TEMPERATURE (OC)
T E M P E R A T U R E (OC )
UVLO Threshold vs Temperature
4.3 0 4.2 8
UVLO THRESHOLD (V)
4.2 5 4.2 3 4.2 0 4.1 8 4.1 5 4.1 3 4.1 0 4.0 8 4.0 5 -5 0 -2 5 0 25 50 75 100 125 150
T E M P E R A T U R E (O C )
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SC2603
POWER MANAGEMENT Outline Drawing - SOT23-6
A
DIM
e1
DIMENSIONS MILLIMETERS INCHES MIN NOM MAX MIN NOM MAX
1.45 0.90 0.00 0.15 .90 1.15 1.30 0.25 0.50 0.08 0.22 2.80 2.90 3.00 1.50 1.60 1.75 2.80 BSC 0.95 BSC 1.90 BSC 0.30 0.45 0.60 (0.60) 6 0 10 0.10 0.20 0.20
D
2X E/2
N
EI
1
ccc C 2X N/2 TIPS
E
2
e
B
D
aaa C
A .035 .057 A1 .000 .006 A2 .035 .045 .051 b .020 .010 c .003 .009 D .110 .114 .118 E1 .060 .063 .069 E .110 BSC e .037 BSC e1 .075 BSC L .012 .018 .024 (.024) L1 N 6 01 0 10 aaa .004 bbb .008 ccc .008
A2
SEATING PLANE
A
H
C
A1
H
c
bxN bbb
C A-B D
GAGE PLANE
0.25
L
01
(L1)
SEE DETAIL
A
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 -H3. DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
Land Pattern - SOT23-6
X
DIM
(C)
DIMENSIONS MILLIMETERS INCHES
(.098) .055 .037 .024 .043 .141 (2.50) 1.40 0.95 0.60 1.10 3.60
G
Y
Z
P
C G P X Y Z
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 93012 Phone: (805)498-2111 FAX (805)498-3804
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