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VOLTAGE MODE PWM CONTROLLER
SC1101
February 29, 2000
TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com
DESCRIPTION
The SC1101 is a versatile, low-cost, voltage-mode PWM controller designed for use in single ended 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.
FEATURES * Low cost / small size * Switch mode efficiency (90%) * 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 ORDERING INFORMATION
DEVICE
(1)
PACKAGE SO-8
TEMP RANGE (TJ) 0 to 125C
SC1101CS
Note: (1) Add suffix `TR' for tape and reel.
PIN CONFIGURATION
BLOCK DIAGRAM
Top View
Vcc Cs(-) Cs(+) GND
1 2 3 4
8 7 6 5
GND FB BST DH
(8 LEAD PLASTIC SOIC)
Pentium is a registered trademark of Intel Corporation
1
(c) 2000 SEMTECH CORP.
652 MITCHELL ROAD NEWBURY PARK CA 91320
VOLTAGE MODE PWM CONTROLLER
SC1101
February 29, 2000
PIN DESCRIPTION
Pin # 1 2 3 4 5 6 7 8 Pin Name VCC 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 (-) Small Signal Ground
ABSOLUTE MAXIMUM RATINGS
Parameter Input Voltage Ground Differential Boost Input Voltage Operating Temperature Storage Temperature Lead Temperature (Soldering) 10 seconds Thermal Resistance, Junction to Ambient Thermal Resistance, Junction to Case Symbol VCC to GND PGND to GND BST to GND TA TJ TL JA JC Maximum -0.3 to +7 1 -0.3 to +15 0 to +70 -45 to +125 300 165 40 Units V V V C C C C/W C/W
2 (c) 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
VOLTAGE MODE PWM CONTROLLER
SC1101
February 29, 2000
ELECTRICAL CHARACTERISTICS
VCC = 4.75V to 5.25V; GND = PGND = 0V; VO = 3.3V; TA = 25C; BST = 12V; Output current = 2A. Per test circuit, unless otherwise specified. PARAMETER Reference SYMBOL VREF Over Temp Feedback Bias Current Quiescent Current Regulation Load Regulation Line Current Limit Threshold Oscillator Frequency Oscillator Frequency Shift Max Duty Cycle DH Sink/Source Current UVLO Threshold IFB IQ REGLOAD REGLINE CLT OSC OFS d.c. IO VUVLO VBST - VDH = 4.5V (VDH - VPGND = 2V) VFB < VREF/2 90 500 3.8 CS(+) to CS(-) 60 180 70 200 50 95 Current into VCC pin IO=1A to 12A CONDITIONS MIN 1.238 1.225 TYP 1.250 1.250 2.0 5.0 0.5 MAX 1.263 1.275 8.0 8.0 1.0 0.5 80 220 UNITS V V uA mA % % mV kHz kHz % mA V
TEST CIRCUIT
J1 +5V + C3 1500uF C1 0.1uF J3 C5 1500uF J4 +12V C7 1500uF + C2 1500uF C4 1500uF + R2 10 + + Q1 BUK556 4uH + + R3 See Table C9 0.1uF R4 See Table D1 PSR16C30CT L1 R1 5mOhm C6 1500uF C8 1500uF J2
VOUT
VOUT R3 3.45 3.30 3.10 2.90 2.80 2.50 1.50 174 165 147 133 124 100 20
R4 100 100 100 100 100 100 100
R5 1.00k U1 1 2 R6 2.32k 3 4 C10 0.1uF VCC CS(-) CS(+) PGND SC1101CS GND FB BST DH 8 7 6 5
C11 0.1uF
VOUT=1.25*(R3+R4)/R4
3 (c) 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
VOLTAGE MODE PWM CONTROLLER
SC1101
February 29, 2000
40 35 30 25 Phase (deg) Gain (dB) 20 15 10 5 0 -5
-0.02
180
0.05
135
Voltage change (V) normalized to 0 at Io=2A
0.04
0.03
90
0.02
Gain Phase
45
0.01
0
0
-0.01
-10 100.0E+0
1.0E+3
10.0E+3
100.0E+3
1.0E+6
-45 10.0E+6
0.0
2.0
4.0
6.0 8.0 Output Current (Amps)
10.0
12.0
14.0
Frequency (Hz)
Fig.1: Error Amplifier, Gain and Phase
Fig.2: Load Regulation Characteristic
100%
95%
90%
Efficiency
85%
80%
75%
3.50V 3.00V 2.40V 2.00V
Set Set Set Set
70%
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
Output Current (Amps)
Fig.3: Ripple; Vo=2.90V; Io=10A
Fig.4: Efficiency
4 (c) 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
VOLTAGE MODE PWM CONTROLLER
SC1101
February 29, 2000
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.
nection 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 2). The loop formed by the Input Capacitor(s) (Cin), the isolated ground. This isolated ground area should be connected to the main ground by a trace that runs from Top FET (Q1) and the Schottky (D1) must be kept as small as possible. This loop contains all the high current, the GND pin to the ground side of (one of) the output cafast transition switching. Connections should be as wide pacitor(s). If this is not possible, the GND pin may be connected to the ground path between the Output Caand as short as possible to minimize loop inductance. Minimizing this loop area will reduce EMI, lower ground pacitor(s) and the Cin, Q1, D1 loop. Under no circumstances should GND be returned to a ground inside the injection currents, resulting in electrically "cleaner" grounds for the rest of the system and minimize source Cin, Q1, D1 loop. ringing, resulting in more reliable gate switching signals. 6) Vcc for the SC1101 should be supplied from the 5V supply through a 10 resistor, the Vcc pin should be de3). The connection between the junction of Q1, D1 and the output inductor should be a wide trace or copper re- coupled directly to GND by a 0.1F ceramic capacitor, gion. It should be as short as practical. Since this contrace lengths should be as short as possible.
12V IN
5V
10
0.1uF 2.32k Cin SC1101CS 1 2 3 0.1uF 4 VCC CS(-) CS(+) PGND GND FB BST DH 8 7 Rb 6 5 D1 Cout 4uH + Q1 + 1.00k 5mOhm Vout
Ra
Heavy lines indicate high current paths.
Fig. 5 Layout diagram for the SC1101 5 (c) 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
VOLTAGE MODE PWM CONTROLLER
SC1101
February 29, 2000 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. The 0.1F capacitor should be mounted as close to the CS(+) and CS(-) pins as possible. 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.
TYPICAL APPLICATIONS
J1 1 +3.3V + C3 220uF C1 0.1uF J3 1 GND + C2 220uF D1 32CTQ030S C4 220uF + C5 220uF + C6 0.1uF R4 124 R2 24 C7 0.01uF J5 1 Q1 IRL2203S L1 R1 6mOhm VOUT J2 1
J4 1 +12V
R5 1k J6 1 +5V R3 10
R6 1k 1 2 3 C10 0.1uF
U1 SC1101CS VCC CS(-) CS(+) PGND GND FB BST DH 8 7 6 5
Cx 0.01
C2-C7 - AVX: TPSE227M010S0100 Q1, D1 - International Rectifier L1- Coilcraft: DO5022P-392HC
4
C9 0.1uF
C8 0.1uF
Fig. 6: GTL+ 3.3V to 1.5V 8A Application
6 (c) 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
VOLTAGE MODE PWM CONTROLLER
SC1101
February 29, 2000
TYPICAL APPLICATIONS (cont.)
D2 LL42
C8 0.1uF
Q1 IRL2203S
L1
+5V
+ + C2 220uF C3 220uF C4 220uF + R3 10
R1 0.012
+3.3V
+ C5 220uF + C6 220uF R2 205 C7 0.1uF R4 124
C1 0.1uF
D1 32CTQ030
GND
R5 1k 1 2 3 R6 1k C10 0.1uF 4
U1 SC1101CS VCC CS(-) CS(+) PGND GND FB BST DH 8 7 6 5
Cx 0.01
C9 0.1uF
C2-C7 - AVX: TPSE227M01S0100 Q1, D1 - International Rectifier L1 - Coilcraft: DO5022P-392HC
Fig. 7: 5V to 3.3V 8A Application with flying capacitor boost
7 (c) 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320
VOLTAGE MODE PWM CONTROLLER
SC1101
February 29, 2000
OUTLINE DRAWING
JEDEC REF: MS-012AA
LAND PATTERN SO-8
ECN00-900
8 (c) 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320

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