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Asynchronous Voltage Mode PWM Controller
POWER MANAGEMENT Description
The SC1101 is a versatile, low-cost, voltage-mode PWM controller designed for low output voltage DC/DC power supply applications. A simple, fixed-voltage buck regulator can be implemented using the SC1101 with a minimum of external components. Internal level shift and drive circuitry eliminates the need for an expensive p-channel, high-side switch. The small device footprint allows for compact circuit design. SC1101 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 SC1101 operates at a fixed frequency of 200kHz, providing an optimum compromise between efficiency, external component size, and cost.
SC1101
Features
Low cost / small size Switch mode efficiency up to 95% 1% reference voltage accuracy Over current protection 500mA output drive SO-8 package
Applications
Pentium(R) P55 Core Supply Low Cost Microprocessor Supplies Peripheral Card Supplies Industrial Power Supplies High Density DC/DC Conversion
Typical Application Circuit
Q1 IRLR3103
L1 4uH
R5 0.05
Vout = 2V @ 10A +
C8 330/2.5V C9 330/2.5V C10 330/2.5V C11 1.0 R6 76.8 *see note R7 127
+5V
C1 1.0
C2 150/6.3V
C3 150/6.3V
D2 MBRD1035L
GND
GND
+12V
R1 10
R2 1k
R3 1k 1
U1 SC1101 VCC GND 8
C6 0.01
R4 2.2
2 C4 0.1 C5 0.001 3
CS(-)
FB
7
CS(+)
BST
6 C7 0.1
4
PGND
DH
5
* NOTE: R6 = R7 x (Vout/1.25 - 1) rounded to nearest 1%value
Revision: May 25, 2005
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SC1101
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 Ground Differential Boost Input Voltage Operating Ambient Temperature Range Storage Temperature Range Maximum Junction Temperature Lead Temperature (Soldering) 10 Sec. Thermal Resistance Junction to Ambient Thermal Resistance Junction to Case
Symbol VCC to GND PGND to GND BST to GND TAMB TSTG TJ TLEAD J A J C
Maximum -0.3 to +7 1 -0.3 to +15 0 to +70 -45 to 125 125 300 165 40
Units V V V C C C C C/W C/W
Electrical Characteristics
Unless specified: VCC = 4.75 to 5.25, GND = PGND = 0V, VO = 2.5V, TA = 25C, BST = 12V. Per test circuit, unless otherwise specified.
Parameter Reference
Symbol VREF
Conditions
Min 1.238
Typ 1.250 1.250 2.0
Max 1.263 1.275 8.0 8.0 1.0 0.5
Units V
Over 0 to 125C Temp. range Feedback Bias Current Quiescent Current Load Regulation Line Regulation Current Limit Threshold Oscillator Frequency Oscillator Frequency Shift Max Duty Cycle DH Sink/Source Current UVLO Threshold IO VUVLO VBST - VDH = 4.5V / VDH -VPGND = 2V VFB < VREF/2 IFB IQ Current into VCC pin IO = 1A to 10A IO = 10A CS(+) to CS(-)
1.225
uA mA % % mV kHz kHz % mA
5.0 0.5
60 170
70 200 50
80 230
90 500
95
3.8
V
Note: (1) This device is ESD sensitive. Use of standard ESD handling precautions is required.
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SC1101
POWER MANAGEMENT Pin Configuration
Top View
VCC CS(-) CS(+) PGND 1 2 3 4 8 7 6 5 GND FB BST DH
Ordering Information
Device
(1)
P ackag e SO-8
Temp Range (TJ) 0 to 125C
SC1101CS.TR SC1101CSTRT(2)
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.
(8 Lead Plastic SOIC)
Pin Descriptions
Pin Number 1 2 3 4 5 6 7 8 Pin Name VC C CS(-) CS(+) PGND DH BST FB GND Pin Function Device input voltage. Current sense input (Negative) . Current sense input (Positive) . Device power ground . High side driver output . High side driver VCC (Boost) . Error amplifier input (-) . Signal ground .
Block Diagram
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SC1101
POWER MANAGEMENT Applications Information
Layout Guidelines Careful attention to layout requirements are necessary for successful implementation of the SC1101 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 Input Capacitor(s) (Cin), the Top FET (Q1) 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 inductor 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. The connection between the output inductor and the sense resistor should be a wide trace or copper area, there are no fast voltage or current transitions in this connection and length is not so important, however adding unnecessary impedance will reduce efficiency. 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 SC1101 is best placed over an isolated ground plane area. GND and PGND should be returned to this isolated ground. 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 (one of) the output capacitor(s). If this is not possible, the GND pin may be connected to the ground path between the Output Capacitor(s) and the Cin, Q1, D1 loop. Under no circumstances should GND be returned to a ground inside the Cin, Q1, D1 loop. 6) Vcc for the SC1101 should be supplied from the 5V supply through a 10 resistor, the Vcc pin should be decoupled directly to GND by a 0.1F ceramic capacitor, trace lengths should be as short as possible. 7) The Current Sense resistor and the divider across it should form as small a loop as possible, the traces running back to CS(+) and CS(-) on the SC1101 should run parallel and close to each other. 8) To minimize noise pickup at the sensitive FB pin, the feedback resistors should both be close to the SC1101 with the bottom resistor (Rb) returned to ground at the GND pin. Under Voltage Lockout The under voltage lockout circuit of the SC1101 assures that the high-side MOSFET driver outputs remain in the off state whenever the supply voltage drops below set parameters. Lockout occurs if VCC falls below 3.8V. Normal operation resumes once VCC rises above 3.8V.
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SC1101
POWER MANAGEMENT Applications Information (Cont.)
Layout diagram for the SC1101 VO = VREF (1 + Ra/Rb)
12V IN 5V
10
0.1uF Cin
SC1101CS 1 2 3 0.001uF 4 VCC CS(-) CS(+) PGND GND FB BST DH 8 7 6 5
Q1
+
Vout Rb D1 4uH + Cout
Ra
Heavy lines indicate high current paths.
Application Circuit 5V to 2.0V @ 10A (Bootstrapped)
D1 LL42 C7 0.1
Q1 IRLR3103
L1 4uH
R5 0.05
+5V
C8 330/2.5V C9 330/2.5V C10 330/2.5V C11 1.0
+
R6 76.8 *see note R7 127
C1 1.0
C2 150/6.3V
C3 150/6.3V
D2 MBRD1035L
Vout = 2V @ 10A
GND
GND
R1 10
R2 1k
R3 1k 1 VCC
U1 SC1101 GND 8
C6 0.01
R4 2.2
2 C4 0.1 C5 0.001 3
CS(-)
FB
7
CS(+)
BST
6
4
PGND
DH
5
* NOTE: R6 = R7 x (Vout/1.25 - 1) rounded to nearest 1%value
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SC1101
POWER MANAGEMENT Typical Characteristics
Error Amplifier, Gain and Phase
40 180
Load Regulation VIN = 5V
PIN Descriptions
35 30 25 Gain (dB) 20 15 Gain 10 5 0 -5 -10 100.0E+0 Phase
1.0% 0.8% 0.6% 0.4%
Phase (deg)
135
90
0.2% 0.0% -0.2% -0.4% -0.6% -0.8% -1.0% 0 2 4 6 Output Current, (A) 8 10 12
3.3V 2.5V 1.8V
45
0
1.0E+3
10.0E+3
100.0E+3
1.0E+6
-45 10.0E+6
Frequency (Hz)
Line Regulation VO = 2.5V; IO = 10A
Efficiency VIN = 5V
2.0% 1.5% 1.0% 0.5% 0.0% -0.5% -1.0% -1.5% -2.0% 4.500 4.750 5.000 Input Voltage, (V) 5.250 5.500
100% 95% 90% 85% 80% 75% 70% 65% 60% 0 2 4 6 Output Current, (A) 8 10 12 3.3V 2.5V 1.8V
Output Ripple Voltage VIN = 5V; VO = 3.3V; IO = 10A
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SC1101
POWER MANAGEMENT Outline Drawing - SO-8
A N 2X E/2 E1 E 1 ccc C 2X N/2 TIPS 2 e/2 B D aaa C SEATING PLANE A2 A C bxN bbb A1 C A-B D GAGE PLANE 0.25 SEE DETAIL 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 AA.
e
D
DIM
A A1 A2 b c D E1 E e h L L1 N 01 aaa bbb ccc
DIMENSIONS MILLIMETERS INCHES MIN NOM MAX MIN NOM MAX
.069 .053 .010 .004 .065 .049 .020 .012 .010 .007 .189 .193 .197 .150 .154 .157 .236 BSC .050 BSC .010 .020 .016 .028 .041 (.041) 8 0 8 .004 .010 .008 1.75 1.35 0.25 0.10 1.65 1.25 0.31 0.51 0.17 0.25 4.80 4.90 5.00 3.80 3.90 4.00 6.00 BSC 1.27 BSC 0.25 0.50 0.40 0.72 1.04 (1.04) 8 8 0 0.10 0.25 0.20
h h
H
c
A
L (L1) DETAIL
01
A
Minimum Land Pattern - SO-8
X
DIM
(C) G Z C G P X Y Z
DIMENSIONS INCHES MILLIMETERS
(.205) .118 .050 .024 .087 .291 (5.20) 3.00 1.27 0.60 2.20 7.40
Y P
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.
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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