VOLTAGE MODE PWM CONTROLLER SC1101 TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com February 29, 2000 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® P55 Core Supply • Low Cost Microprocessor Supplies • Peripheral Card Supplies • Industrial Power Supplies • High Density DC/DC Conversion ORDERING INFORMATION (1) DEVICE SC1101CS PACKAGE TEMP RANGE (TJ) SO-8 0° to 125°C Note: (1) Add suffix ‘TR’ for tape and reel. BLOCK DIAGRAM PIN CONFIGURATION Top View Vcc 1 8 GND Cs(-) 2 7 FB Cs(+) 3 6 BST GND 4 5 DH (8 LEAD PLASTIC SOIC) Pentium is a registered trademark of Intel Corporation © 2000 SEMTECH CORP. 1 652 MITCHELL ROAD NEWBURY PARK CA 91320 VOLTAGE MODE PWM CONTROLLER SC1101 February 29, 2000 PIN DESCRIPTION Pin # Pin Name Pin Function 1 VCC Device Input Voltage 2 Cs(-) Current Sense Input (Negative) 3 Cs(+) Current Sense Input (Positive) 4 PGND Device Power Ground 5 DH High Side Driver Output 6 BST High Side Driver VCC (Boost) 7 FB 8 GND Error Amplifier Input (-) Small Signal Ground ABSOLUTE MAXIMUM RATINGS Parameter Input Voltage Symbol VCC to GND Maximum -0.3 to +7 Units V Ground Differential PGND to GND ±1 V Boost Input Voltage BST to GND -0.3 to +15 V Operating Temperature TA 0 to +70 °C Storage Temperature TJ -45 to +125 °C Lead Temperature (Soldering) 10 seconds TL 300 °C Thermal Resistance, Junction to Ambient θ JA 165 °C/W Thermal Resistance, Junction to Case θ JC 40 °C/W 2 © 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 = 25°C; BST = 12V; Output current = 2A. Per test circuit, unless otherwise specified. PARAMETER SYMBOL Reference CONDITIONS VREF Over Temp MIN TYP MAX UNITS 1.238 1.250 1.263 V 1.225 1.250 1.275 V 2.0 8.0 uA Feedback Bias Current IFB Quiescent Current IQ Current into VCC pin 5.0 8.0 mA Regulation Load REGLOAD IO=1A to 12A 0.5 1.0 % Regulation Line REGLINE 0.5 % Current Limit Threshold CLT Oscillator Frequency OSC Oscillator Frequency Shift OFS Max Duty Cycle d.c. DH Sink/Source Current CS(+) to CS(-) 70 80 mV 180 200 220 kHz VFB < VREF/2 90 50 kHz 95 % 500 VBST - VDH = 4.5V (VDH - VPGND = 2V) IO UVLO Threshold 60 mA 3.8 VUVLO V TEST CIRCUIT Q1 J1 D1 PSR16C30CT L1 R1 5mOhm BUK556 +5V C6 1500uF C8 1500uF J2 VOUT 4uH + C3 1500uF C1 0.1uF + + C2 1500uF + + R2 10 R3 See Table C9 0.1uF C4 1500uF + + C5 1500uF C7 1500uF R4 See Table J3 J4 +12V VOUT R3 R4 3.45 174 100 3.30 165 100 1 3.10 147 100 2 2.90 133 100 2.80 124 100 2.50 100 100 1.50 20 100 R5 1.00k U1 3 R6 2.32k C11 0.1uF 4 C10 0.1uF VCC GND CS(-) FB CS(+) BST PGND DH SC1101CS 8 7 6 5 VOUT=1.25*(R3+R4)/R4 3 © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320 VOLTAGE MODE PWM CONTROLLER SC1101 February 29, 2000 40 180 0.05 35 30 135 0.04 90 15 Gain Phase 10 45 5 0 0.03 Voltage change (V) normalized to 0 at Io=2A 20 Phase (deg) Gain (dB) 25 0 0.02 0.01 0 -0.01 -5 -0.02 -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% Efficiency 90% 85% 80% 3.50V 3.00V 2.40V 2.00V 75% 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 © 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 10Ω 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 0.1µF 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 Q1 SC1101CS 1 2 3 0.1uF 4 VCC GND CS(-) FB CS(+) BST PGND DH + 1.00k 8 5mOhm Vout 7 4uH Rb 6 + D1 Cout 5 Ra Heavy lines indicate high current paths. Fig. 5 Layout diagram for the SC1101 5 © 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 0.1µF capacitor should be mounted as close to the CS(+) and CS(-) pins as possible. 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. 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. TYPICAL APPLICATIONS Q1 IRL2203S J1 1 L1 R1 6mOhm J2 +3.3V VOUT + C3 220uF C1 0.1uF C4 220uF D1 32CTQ030S + C2 220uF 1 C6 0.1uF + C5 220uF J3 1 R2 24 + GND R4 124 C7 0.01uF J5 1 J4 1 +12V R5 1k J6 1 +5V R6 1k R3 10 U1 SC1101CS 1 2 3 C2-C7 - AVX: TPSE227M010S0100 Q1, D1 - International Rectifier L1- Coilcraft: DO5022P-392HC C10 0.1uF C9 0.1uF 4 VCC CS(-) GND FB CS(+) BST PGND DH 8 Cx 0.01 7 6 5 C8 0.1uF Fig. 6: GTL+ 3.3V to 1.5V 8A Application 6 © 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 R1 0.012 +5V +3.3V + C1 0.1uF + + C3 220uF C2 220uF + C4 220uF R3 10 R2 205 C5 220uF D1 32CTQ030 C7 0.1uF + C6 220uF GND R5 1k U1 SC1101CS 1 2 3 R6 1k C9 0.1uF 4 VCC GND CS(-) FB CS(+) BST PGND DH R4 124 Cx 0.01 8 7 6 5 C10 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 © 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 © 2000 SEMTECH CORP. 652 MITCHELL ROAD NEWBURY PARK CA 91320