SC198 Dual DC-DC Buck Converter with High Current Capability POWER MANAGEMENT Features Description The SC198 is a high-efficiency, dual synchronous buck converter designed for use in low power applications. Each converter is capable of supplying up to 600mA of average current at one of eight programmable output voltages commonly used as microprocessor supply voltages. Dual buck converters with independent control High efficiency - over 90% peak 8 programmable output voltages Input voltage range between 2.7V to 5.5V Fixed-frequency operation - 1MHz Optional SYNC clock input Optional power-save under light-load conditions Shutdown current <1μA Soft-start to limit in-rush current 4mm x 4mm MLPQ package The SC198 uses a single control logic block for the two converters, but their controls can be set independently. The SC198 employs a flexible clocking scheme that allows the user to use the fixed internal 1MHz oscillator or synchronize the clock to an external source. The device also has an optional power-save mode that optimizes efficiency for light loads. The SC198 provides output voltage flexibility while conserving board space by using control pins to select the output voltage instead of external resistor voltage divider circuits. This eliminates at least four parts from the traditional dual buck converter bill of materials. Applications Mobile phones Cordless phones MP3 players Digital cameras PDAs Single li-ion cell or (3) NiMH/NiCd cell devices Digital multimedia broadcast (DMB) devices Portable gaming systems Typical Application Circuit 1 18 15 10μF 20 5 6 7 16 11 10 9 17 March 28, 2007 VINA SC198 LXA VINR VOUTA VINB GNDA ENA 2 4.7μH VOUTA 4 3 10μF CTLA0 CTLA1 CTLA2 LXB ENB VOUTB GNDB CTLB0 CTLB1 GNDR CTLB2 14 4.7μH VOUTB 12 13 10μF 8 SYNC www.semtech.com 1 SC198 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 recommended. Parameter Symbol Maximum Units VIN -0.3 to 7 V EN, SYNC Input VEN ,VSYNC -0.3 to VIN +0.3 V LXA and LXB Voltages VLXA, VLXB -1 to VIN +1 V VOUT -0.3 to VIN +0.3 V -0.3 to VIN +0.3 V tSC Indefinite s ILXA and ILXB 1.2 A Thermal Impedance (Junction to Ambient)(1) θJA 40 ºC/W Operating Ambient Temperature TA -40 to +85 ºC Maximum Junction Temperature TJ 150 ºC Storage Temperature TS -65 to +150 ºC Reflow Solder Temperature TPKG 260 °C ESD Protection Level(2) VESD 2 kV VIN VOUT CTLA0, CTLA1, CTLA2, CTLB0, CTLB1 & CTLB2 Voltages Output Short Circuit to GND LXA and LXB Currents Note: (1) Calculated from package in still air, mounted to 3” x 4.5”, 4 layer FR4 PCB with thermal vias under the exposed pad as per JESD51 standards. (2) Tested according to JEDEC standard JESD22-A114-B. Electrical Characteristics Unless otherwise noted: VIN = 3.6V, SYNC = VIN, L = 4.7μH, C = 10μF, TA = -40°C to +85°C. Typical values are at TA = 25°C. Parameter Input Voltage Range VOUT Accuracy(1) Symbol Conditions VIN Min Typ Max Units 2.7 5.5 V -3 3 % ∆VOUT IOUT = 10mA to 600mA Line Regulation VLINEREG VIN = 2.7 to 5.5V, VOUT = 1.8V, IOUT = 300mA 0.2 %/V Load Regulation VLOADREG IOUT = 10mA to 600mA 0.0008 %/mA 18 % Minimum Duty Cycle DCMIN LXA, LXB Current Limit ILIM Quiescent Current IQ IOUT = 0mA, SYNC = 0, ENA, ENB = VIN Shutdown Current ISD ENA, ENB = 0, LXA, LXB = Open VIN = 5.5V, LX = 0V, PMOS LXA and LXB Leakage Current ILXA, ILXB 0.9 VIN = 5.5V, LX = VIN, NMOS © 2007 Semtech Corp. -2 A 50 μA 0.1 1 μA 0.1 1 μA 0.1 μA www.semtech.com 2 SC198 POWER MANAGEMENT Electrical Characteristics (Cont.) Parameter Symbol Conditions Min Typ P-Channel On Resistance RDSP ILXA, ILXB = 100mA 0.35 Ω N-Channel On Resistance RDSN ILXA, ILXB = 100mA 0.25 Ω Start-Up Time tSTART Oscillator Frequency fOSC 0.85 SYNC Frequency (upper) fSYNCU 1.25 SYNC Frequency (lower) fSYNCL 1.1 Max Units 5 ms 1.25 MHz MHz 0.75 MHz Thermal Shutdown THI 145 °C Thermal Shutdown Hysteresis THYSR 10 °C UVLO Threshold VUVL UVLO Hysteresis VUVLHYS Logic Input High(2) VIH Logic Input Low(2) VIL Decreasing VIN 2.4 2.5 2.6 50 V mV 1.6 V 0.6 V Notes: (1) See Output Voltage Options table in the Application Information section. (2) For ENA, ENB, SYNC, CTLA0, CTLA1, CTLA2, CTLB0, CTLB1, CTLB2. © 2007 Semtech Corp. www.semtech.com 3 SC198 POWER MANAGEMENT Electrical Characteristics (Cont.) Pin Configuration Ordering Information ENA NC VINR SYNC ENB 18 17 16 SC198EVB LXB 3 13 GNDB VOUTA 4 12 VOUTB CTLA0 5 11 CTLB0 7 8 9 10 CTLB1 CTLA1 6 CTLB2 T GNDR GNDA TOP VIEW CTLA2 2 Evaluation Board 19 14 LXA MLPQ-20 20 VINB 1 PACKAGE SC198MLTRT(1)(2) 15 VINA DEVICE (1) Notes: (1) Available in tape and reel only. A reel contains 3,000 devices. (2) Available in lead-free package only. Device is WEEE and RoHS compliant. MLPQ20: 4X4 20 LEAD Marking Information SC198 yyww xxxxx xxxxx yy = two digit year of manufacture ww = two digit week of manufacture xxxxx = lot number © 2007 Semtech Corp. www.semtech.com 4 SC198 POWER MANAGEMENT Pin Descriptions Pin # Pin Name Pin Function 1 VINA Input power supply voltage converter A 2 LXA Connection point for the inductor on converter A 3 GNDA Ground reference to converter A 4 VOUTA Feedback control input for converter A 5 CTLA0 Voltage select control pin 0 for output A (see Table A — Output Voltage Options).(1) 6 CTLA1 Voltage select control pin 1 for output A (see Table A — Output Voltage Options). (1) 7 CTLA2 Voltage select control pin 2 for output A (see Table A — Output Voltage Options). (1) 8 GNDR Ground for reference supply 9 CTLB2 Voltage select control pin 2 for output B (see Table A — Output Voltage Options). (1) 10 CTLB1 Voltage select control pin 1 for output B (see Table A — Output Voltage Options). (1) 11 CTLB0 Voltage select control pin 0 for output B (see Table A — Output Voltage Options). (1) 12 VOUTB Feedback control input for converter B 13 GNDB Ground reference for converter B 14 LXB Connection point for the inductor on converter B 15 VINB Input power supply voltage for converter B 16 ENB Enable pin for output B 17 SYNC Oscillator synchronization input - connect to VIN for forced PWM mode, ground for power-save mode or connect to an external clock for frequency synchronization. 18 VINR Reference supply input 19 NC Not connected 20 ENA Enable pin for output A T THERMAL PAD Thermal pad for heatsinking purposes — connect to ground plane using multiple vias — not connected internally Note: (1) All CTL pins must be pulled high or low for proper operation. © 2007 Semtech Corp. www.semtech.com 5 SC198 POWER MANAGEMENT Block Diagram SYNC Oscillator and Slope Generator VINA Error Amp A VINB Error Amp B VREF1 VREF1 Current Amp PWM Comp P Limit Amp PWM Comp Current Amp P Limit Amp N Limit Amp N Limit Amp LXA LXB Switching Control Logic VREF2 VREF2 GNDA GNDB ENA ENB VOUTA VOUTB CTLA0 Voltage Select VREF3 Error Amp A Error Amp B VREF3 CTLB0 Voltage Select CTLA1 CTLB1 CTLA2 CTLB2 VREF1 VINR Voltage References VREF2 VREF3 GNDR © 2007 Semtech Corp. www.semtech.com 6 SC198 POWER MANAGEMENT Applications Information SC198 Detailed Description The SC198 is a dual step-down, pulse-width modulated DC-DC converter with programmable output voltage and power-save mode. This device has a 1MHz internal oscillator that can be used during forced PWM mode or power-save mode (PSAVE). Programmable Output Voltage The SC198 has three control pins per output to allow the user to select a voltage level from eight predetermined output voltage levels (see Table A, Output Voltage Options below). The output voltage can be selected at any time, including while the output is enabled and loaded. Operation During normal operation, the PMOS switch is activated on each rising edge of the internal oscillator. Current feedback for the switching regulator is through the PMOS current path, and it is amplified and summed with the internal slope compensation network. The voltage feedback loop uses an internal feedback divider. The ontime is determined by comparing the summed current feedback and the output of the error amplifier. The period is set by the onboard oscillator or by an external clock attached to the SYNC/PWM pin. When synchronizing to an external frequency, the SC198 operates in PWM mode only. The device has an internal synchronous NMOS rectifier and does not require a Schottky diode on the LX pin. The device is designed to operate as a buck converter in PWM mode with a fixed frequency of 1MHz. At light loads the part can enter PSAVE mode to maximize efficiency. Table A — Output Voltage Options Programmable Output Voltage Output Filter The SC198 converter also has internal loop compensation. The internal compensation is designed to work with a certain output filter corner frequency defined by the equation: CTLA2/B2 CTLA1/B1 CTLA0/B0 Nominal Output Voltage (V) 0 0 0 1 0 0 1 1.2 0 1 0 1.375 0 1 1 1.4 1 0 0 1.5 1 0 1 1.575 1 1 0 1.8 1 1 1 1.875 Continuous Conduction and Oscillator Synchronization The SC198 is designed to operate in a continuous conduction mode, where it maintains a fixed frequency. When the SYNC pin is tied high, the part runs under control of the internal oscillator in PWM mode. The part can be synchronized to an external clock by connecting a clock signal to the SYNC pin. The part synchronizes to the rising edge of the clock. 1 fC = ————— ——— 2 √ L×C Power-Save Mode Operation The SC198 has a power-save mode (PSAVE) which may be selected by tying the SYNC pin to GND. Selecting PSAVE mode enables automatic activation of PSAVE mode at light loads, thus maximizing efficiency across the full load range. The SC198 will automatically detect the load current at which it should enter PSAVE mode. The SC198 is optimized to track maximum efficiency with respect to VIN. When selecting output filter components, the LC product should not vary over a wide range. Selection of smaller inductor and capacitor values will move the corner frequency, potentially impacting system stability. Due to this issue the practical lower limit for the inductor value is 4.7μH. The internal compensation is designed to operate with a single-pole output filter, L = 4.7μH and COUT = 10μF. © 2007 Semtech Corp. www.semtech.com 7 SC198 POWER MANAGEMENT Applications Information (Cont.) Upper Threshold Limit BURST OFF Protection Features The SC198 provides the following protection features: Higher Load Applied z z z z Lower Threshold Limit PSAVE Mode at Light Load PWM Mode at Medium/ High Load VOUT PSAVE Exit Threshold Thermal Shutdown Current Limit Over-Voltage Protection Soft-Start Thermal Shutdown The device has a thermal shutdown feature to protect the SC198 if the junction temperature exceeds 145°C. In thermal shutdown the on-chip power devices are disabled, tri-stating the LX output. Switching will resume when the temperature drops by 10°C. During this time if the output voltage decreases by more than 60% of its programmed value, a soft-start will be invoked. Inductor Current 0A Time PSAVE Operation Current Limit The PMOS and NMOS power devices of the buck switcher stage are protected by current limit functions. In the case of a short to ground on the output, the part enters frequency foldback mode, that causes the switching frequency to divide by a factor determined by the output voltage. This prevents the inductor current from “staircasing”. In PSAVE mode, VOUT regulation is controlled by bursts in switching. While the output voltage is between the low and high voltage thresholds, switching is stopped to reduce loss in the regulator due to switching. When the voltage drops to the lower threshold, the switch bursts at a fixed on time until the upper threshold is met. At this point the output voltage is allowed to ramp down to the lower threshold again without switching to conserve power. In the PSAVE mode, less switching is used. Less switching results in less power loss which can be seen in the difference of efficiency between PWM mode and PSAVE mode at light loads. Over-Voltage Protection Over-voltage protection is provided on the SC198. Hysteresis is provided to prevent toggling in and out of operation. Soft-Start The soft-start mode operates by limiting the current through the inductor and controlling the switching frequency. The current limit is increased over several milliseconds the in discrete steps. This has the desired effect of limiting inrush current from the input supply. The soft-start mode is cancelled once the output reaches regulation. Soft-start is only re-enabled by power cycling, toggling enable, UVLO event, or shutdown. The PSAVE switching burst frequency is controlled such that the inductor current ripple during the burst is similar to that in PWM mode. The minimum switching frequency during this period is limited to 650kHz. The SC198 automatically detects when to exit PSAVE mode. The device sets a maximum peak current in PSAVE mode, and then detects when VOUT falls due to the load increasing above the level that the peak current will support. For the SC198 to exit PSAVE mode, the load must be increased, which causes VOUT to decrease until the PSAVE exit threshold is reached. PSAVE levels are set high to minimize the undershoot when the SC198 exits PSAVE. © 2007 Semtech Corp. www.semtech.com 8 SC198 POWER MANAGEMENT Applications Information (Cont.) Inductor Selection The SC198 was designed for optimum performance when using a 4.7μH inductor. The magnitude of the inductor current ripple is dependent on the inductor value and can be determined by the following equation: ( Capacitors with X7R or X5R ceramic dielectric are strongly recommended for their low ESR and superior temperature and voltage characteristics. Y5V capacitors should not be used as their temperature coefficients make them unsuitable for this application. Table C lists some manufacturers of recommended capacitor options. ) VOUT VOUT ΔIL = ——— 1 + ——— L × fOSC VIN This equation demonstrates the relationship between input voltage, output voltage, and inductor ripple current. The inductor should also have a low DCR to minimize the conduction losses and maximize efficiency. The minimum DC current rating of the inductor should be equal to the maximum load current plus half of the inductor current ripple as shown by the following equation: ΔIL IL(PK) = IOUT(MAX) + —— 2 Final inductor selection will depend on various design considerations such as efficiency, EMI, size and cost. Table B lists some manufacturers of practical inductor options. Capacitor Selection Input Capacitor The source input current to a buck converter is non-continuous. To prevent large input voltage ripple a low ESR ceramic capacitor is required. A minimum value of 4.7μF should be used for sufficient input voltage filtering and a 22μF MLCC may be used for optimum input voltage filtering. Output Capacitor A 4.7μF ceramic capacitor is the minimum recommended for the output filter capacitor. A capacitor value of at least 10μF is recommended if the part will be used in powersave mode. Output voltage ripple is dominated by the filter capacitance ESR as shown in the following equation: VOUT(P-P) = ΔIL × ESRCOUT © 2007 Semtech Corp. www.semtech.com 9 SC198 POWER MANAGEMENT Applications Information (Cont.) Table B — Recommended Inductors Manufacturer Coilcraft TDK BI Technologies Part Number Value μH DCR Ω Rated Current A Tolerance % Dimensions (L×W×H) mm LPO6610-472ML(1) 4.7 0.20 1.1 ±20 6.60 × 5.50 × 1.10 1812PS-472KLB 4.7 0.11 2.10 ±20 5.87 × 4.89 × 3.81 VLCF4020T-4R7N1R2 4.7 0.098 1.0 ±30 4x4x2 HM66-304R7LF 4.7 0.072 1.32 ±20 4.7 × 4.7 × 3.0 Note: (1) This inductor was used while obtaining data for the Typical Characteristics Section. Table C — Recommended Capacitors Manufacturer Murata AVX Part Number Value μF Rated Voltage VDC Type Case Size GRM21BR60J226ME39 22 6.3 X5R 0805 GRM188R60J106ME47 10 6.3 X5R 0603 GRM188R60J475KE19 4.7 6.3 X5R 0603 08056D107MAT2A 10 6.3 X5R 0805 © 2007 Semtech Corp. www.semtech.com 10 SC198 POWER MANAGEMENT Applications Information (Cont.) PCB Layout Considerations Poor layout can degrade the performance of the DC-DC converter and can be a contributory factor in EMI problems, ground bounce, thermal issues, and resistive voltage losses. Poor regulation and instability can result. The following design rules are recommended: 1. Place the inductor and filter capacitors as close to the device as possible and use short wide traces between the power components. 2. Route the output voltage feedback path away from inductor and LX node to minimize noise and magnetic interference. 3. Use a ground plane to further reduce noise interference on sensitive circuit nodes. VIN CinR CinA CinB LXB LXA SC198 GND GND VOUTB VOUTA Note: Control pin routings are not shown. © 2007 Semtech Corp. www.semtech.com 11 SC198 POWER MANAGEMENT Typical Characteristics Efficiency vs. Load @ 2.7VIN Efficiency vs. Load @ 3.6VIN 90 80 80 70 70 60 50 Efficiency (%) 100 90 Efficiency (%) 100 VOUT = 1.8V PSAVE VOUT = 1V PSAVE 40 VOUT = 1.8V PWM 30 20 VOUT = 1.8V PSAVE 60 50 VOUT = 1V PSAVE 40 VOUT = 1.8V PWM 30 20 VOUT = 1V PWM 10 10 VOUT = 1V PWM ENA=ENB=VIN 0 0.001 0.01 ENA=ENB=VIN 0.1 0 0.001 1 0.01 Load (A) 0.1 1 Load (A) Oscillator Frequency vs. Input Voltage Efficiency vs. Load @ 5.5VIN 100 4.0 90 2.0 Normalized Frequency (kHz) 80 Efficiency (%) 70 60 VOUT = 1.8V PSAVE 50 40 VOUT = 1V PSAVE VOUT = 1.8V PWM 30 20 85°C 0.0 -2.0 25°C -40°C -4.0 -6.0 10 VOUT = 1V PWM 0 0.001 0.01 ENA=ENB=VIN 0.1 -8.0 2.7 1 3.1 3.5 3.9 Load (A) Line Regulation at 300mAOUT 4.7 5.1 5.5 Load Regulation at 3.6VIN (PWM) 0.2 1 0.8 0.15 VOUT = 1V 0.6 0.1 0.4 0.05 Output (%) Output (%) 4.3 Input (V) 0 VOUT = 1.8V -0.05 VOUT = 1.8V 0.2 0 -0.2 VOUT = 1V -0.4 -0.1 -0.6 -0.15 -0.8 -1 0.001 -0.2 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 0.01 0.1 1 Load (A) Input (V) © 2007 Semtech Corp. www.semtech.com 12 SC198 POWER MANAGEMENT Typical Characteristics (Cont.) Efficiency vs. Line @ VOUT = 1.8V Efficiency vs. Line @ VOUT = 1V 100 100 30mA PSAVE 30mA PSAVE 90 Efficiency (%) Efficiency (%) 90 80 300mA Load 70 80 70 30mA PWM 30mA PWM 60 60 300mA Load 50 50 2.7 3.7 2.7 4.7 3.7 4.7 Input (V) Input (V) Output Ripple for VIN = 3.6V and VOUT = 1.8V @ IOUT = 10mA Output Ripple for VIN = 3.6V and VOUT = 1.8V @ IOUT = 50mA 20mV/div 20mV/div VIN 10mV/div VOUT VIN 10mV/div VOUT 2.0V/div 2.0V/div LX LX 400ns/div 400ns/div PSAVE @ 50mA Load 50mV/div 50mV/div PSAVE @ 30mA Load 50mV/div VIN VOUT VIN 50mV/div 2V/div VOUT 2V/div LX LX 4μs/div 4μs/div © 2007 Semtech Corp. www.semtech.com 13 SC198 POWER MANAGEMENT Typical Characteristics (Cont.) Transient Step in PSAVE PSAVE @ 50mA Load with COUT = 22μF 50mV/div 200mV/div VIN VIN 50mV/div 200mV/div VOUT VOUT 5.0V/div LX 2.0V/div 200mA/div LX IOUT 400μs/div 4.0μs/div Input Transient Step from 3.1V to 3.6V Input Transient Step from 3.6V to 3.1V 500mV/div 500mV/div VIN 20mV/div 20mV/div VOUT VOUT 50mV/div VIN 1ms/div 1ms/div Output Transient @ PWM Output Transient in PSAVE 50mV/div VOUTA VOUTA C 2V/div 2V/div CTL0 1 and 2 2ms/div CTL0 1 and 2 2ms/div © 2007 Semtech Corp. www.semtech.com 14 SC198 POWER MANAGEMENT Outline Drawing - MLPQ-20 4 x 4 A D B DIM PIN 1 INDICATOR (LASER MARK) A A1 A2 b D D1 E E1 e L N aaa bbb E A2 A DIMENSIONS INCHES MILLIMETERS MIN NOM MAX MIN NOM MAX .031 .035 .040 .000 .001 .002 - (.008) .007 .010 .012 .153 .157 .161 .100 .106 .110 .153 .157 .161 .100 .106 .110 .020 BSC .011 .016 .020 20 .004 .004 0.80 0.90 1.00 0.00 0.02 0.05 - (0.20) 0.18 0.25 0.30 3.90 4.00 4.10 2.55 2.70 2.80 3.90 4.00 4.10 2.55 2.70 2.80 0.50 BSC 0.30 0.40 0.50 20 0.10 0.10 SEATING PLANE aaa C A1 C D1 LxN E/2 E1 2 1 N bxN bbb C A B e D/2 NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS THE TERMINALS. © 2007 Semtech Corp. www.semtech.com 15 SC198 POWER MANAGEMENT Land Pattern - MLPQ-20 4 x 4 K DIMENSIONS (C) G H Z Y DIM C G H K P X Y Z INCHES (.155) .122 .106 .106 .021 .010 .033 .189 MILLIMETERS (3.95) 3.10 2.70 2.70 0.50 0.25 0.85 4.80 X 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 93012 Phone: (805) 498-2111 Fax: (805) 498-3804 www.semtech.com © 2007 Semtech Corp. www.semtech.com 16