SC198A Dual DC-DC Buck Converter with High Current Capability POWER MANAGEMENT Features Description The SC198A is a dual high-efficiency synchronous buck converter designed for use in low power applications. Each converter is capable of supplying up to 800mA of average current at one of eight programmable output voltages used as microprocessor supply voltages. Input voltage range — 2.7V to 5.5V Dual buck converters with independent control High efficiency — over 90% peak Up to 800mA Load Programmable output voltages per channel — 8 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 SC198A uses a single control logic block for the two converters, but their controls can be set independently. The device uses a flexible clocking method allowing the user to set 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. 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 The SC198A provides output voltage flexibility while conserving board space by using control pins to select the output voltage. This eliminates at least four parts from the traditional dual buck converter bill of materials. Typical Application Circuit VINA VBATT SC198A VINR VINB CIN ENA 4.7μH VOUTA LXA VOUTA COUTA GNDA CTLA0 CTLA1 CTLA2 ENB CTLB0 4.7μH VOUTB LXB VOUTB GNDB COUTB CTLB1 CTLB2 GNDR MODE/SYNC September 26, 2007 1 SC198A NC VINR MODE/SYNC ENB Ordering Information ENA Pin Configuration 20 19 18 17 16 15 VINB 14 LXB 3 13 GNDB VOUTA 4 12 VOUTB CTLA0 5 11 CTLB0 T 6 7 8 9 10 CTLB1 GNDA TOP VIEW CTLB2 2 GNDR LXA CTLA2 1 CTLA1 VINA Device Package SC198AMLTRT(1) (2) MLPQ-20 SC198AEVB Evaluation Board Notes: (1) Available in tape and reel only. A reel contains 3,000 devices. (2) Lead-free package only. Device is WEEE and RoHS compliant. MLPQ: 4mm x 4mm 20 Lead θJA = 31°C/W Marking Information 198A yyww xxxxx xxxxx yyww = Date Code xxxx = Semtech Lot No. xxxx = Semtech Lot No. 2 SC198A Absolute Maximum Ratings Recommended Operating Conditions VIN (V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +7 Ambient Temperature Range (°C) . . . . . . . . . . . . . -40 to +85 VOUT (V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to VIN +0.3 VIN (V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7 to 5.5 VLXA and VLXB (V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .-1 to VIN +1 Pin Voltage - All Other Pins (V) . . . . . . . . . -0.3 to (VIN + 0.3) Output Short Circuit to GND Duration . . . . . Continuous Thermal Information LXA and LXB Currents (A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Thermal Resistance, Junction to Ambient(2) (°C/W) . . . . 31 ESD Protection Level(1) (kV) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Maximum Junction Temperature (°C) . . . . . . . . . . . . . . +150 Storage Temperature Range (°C) . . . . . . . . . . . . -65 to +150 Peak IR Reflow Temperature (10s to 30s) (°C) . . . . . . . +260 Exceeding the above specifications 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. NOTES: (1) Tested according to JEDEC standard JESD22-A114-B. (2) Calculated from package in still air, mounted to 3 x 4.5 (in), 4 layer FR4 PCB with thermal vias under the exposed pad per JESD51 standards. Electrical Characteristics Unless otherwise noted: VIN = 3.6V, VMODE/SYNC = VIN, L = 4.7μH, C = 10μF, TA = -40°C to +85°C. Typical values are at TA = 25°C for both outputs. Parameter Input Voltage Range Symbol Conditions Min Typ Max VOUT = 1.8V 2.7 5.5 VOUT = 3.3V 4.0 5.5 IOUT = 10mA to 800mA , VIN ≥ 0.7V + VOUT -3 3 % 0.2 %/V 0.0008 %/mA 18 % VIN VOUT Accuracy(1) ΔVOUT Line Regulation ΔVLINE Units V VIN = 2.7 to 5.5V, VOUT = 1.8V, IOUT = 300mA VIN = 4.0 to 5.5V, VOUT = 3.3V, IOUT = 300mA IOUT = 10mA to 800mA, VOUT = 1.8V Load Regulation ΔVLOAD IOUT = 10mA to 800mA, VOUT = 3.3V, VIN = 5.0V Minimum Duty Cycle DCMIN LXA, LXB Current Limit ILIM Quiescent Current IQ IOUT = 0mA, SYNC = 0, ENA, ENB = VIN Shutdown Current ISD VENA, VENB = 0, LXA, LXB = Open VIN = 5.5V, VLX = 0V, PMOS LXA and LXB Leakage Current P-Channel On Resistance 1.2 A 50 μA 0.1 1 μA 0.1 1 μA ILXA, ILXB VIN = 5.5V, VLX = VIN, NMOS RDSP ILXA, ILXB = 100mA -2 0.1 μA 0.35 Ω 3 SC198A Electrical Characteristics (continued) Parameter Symbol Conditions Min N-Channel On Resistance RDSN ILXA, ILXB = 100mA Start-Up Time tSTART Oscillator Frequency fOSC 0.95 SYNC Frequency (upper) fSYNCU 1.25 SYNC Frequency (lower) fSYNCL Typ Max 0.25 1.1 Units Ω 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. 4 SC198A Pin Descriptions Pin # Pin Name Pin Function 1 VINA Input power supply voltage for 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 1 — Output Voltage Options). 6 CTLA1 Voltage select control pin 1 for output A (see Table 1 — Output Voltage Options). 7 CTLA2 Voltage select control pin 2 for output A (see Table 1 — Output Voltage Options). 8 GNDR Ground for reference supply 9 CTLB2 Voltage select control pin 2 for output B (see Table 1 — Output Voltage Options). 10 CTLB1 Voltage select control pin 1 for output B (see Table 1 — Output Voltage Options). 11 CTLB0 Voltage select control pin 0 for output B (see Table 1 — Output Voltage Options). 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 MODE/SYNC 18 VINR 19 NC Not connected — Leave open 20 ENA Enable pin for output A T THERMAL PAD Oscillator synchronization input — connect to VIN for forced PWM mode, ground for power-save mode or connect to an external clock for frequency synchronization. Reference supply input Thermal pad for heatsinking purposes — connect to ground plane using multiple vias — not connected internally 5 SC198A Block Diagram SYNC 17 Oscillator and Slope Generator VINA 1 VREF1 Current Amp P Limit Amp Error Amp A Error Amp B PWM Comp 15 VINB VREF1 PWM Comp N Limit Amp LXA 2 P Limit Amp Current Amp N Limit Amp 14 LXB Switching Control Logic VREF2 VREF2 13 GNDB GNDA 3 ENA 20 16 ENB VOUTA 4 12 VOUTB CTLA0 5 CTLA1 6 Voltage Select VREF3 Error Amp A Error Amp B CTLA2 7 VINR 18 VREF3 Voltage Select 11 CTLB0 10 CTLB1 9 CTLB2 Voltage References VREF1 VREF2 VREF3 8 GNDR 6 SC198A Typical Characteristics Efficiency vs. Load at VIN = 2.7V, Side A 100 Efficiency vs. Load at VIN = 3.6V, Side A 100 VOUT = 1.8V PSAVE 90 90 VOUT = 1.0V PSAVE 80 VOUT = 1.0V PSAVE 80 70 70 VOUT = 1.8V PWM 60 Efficiency (%) Efficiency (%) VOUT = 1.8V PSAVE VOUT = 1.0 PWM 50 40 30 60 VOUT = 1.8V PWM 50 40 VOUT = 1.0 PWM 30 20 20 10 10 0 0 0.001 0.01 0.1 1 0.001 Load (A) 0.01 0.1 1 Load (A) Efficiency vs. Load at VIN = 5.5V, Side A Efficiency vs. Load at VIN = 5.5V, Side B 100 100 VOUT = 1.8V PSAVE 90 90 VOUT = 1.8V PSAVE 80 VOUT = 1.0V PSAVE 70 Efficiecny (%) 70 Efficiecny (%) VOUT = 1.0V PSAVE 80 60 50 VOUT = 1.8V PWM 40 VOUT = 1.0 PWM 30 60 VOUT = 1.8V PWM 50 40 VOUT = 1.0 PWM 30 20 20 10 10 0 0 0.001 0.1 0.01 0.001 1 0.01 1 0.1 Load (A) Load (A) Line Regulation at 300mA Load Regulation — VOUT=1.8V, VIN=3.6V 0.2 3 VOUT = 1.8V PWM 0.15 2 0.1 1 Output (%) Output (%) VOUT = 1.0 PWM 0.05 0 VOUT = 1.8V PWM 0 VOUT = 1.0 PWM -0.05 -1 -0.1 -2 -0.15 -3 -0.2 2.7 3.26 3.82 4.38 Input (V) 4.94 5.5 0.001 0.01 0.1 1 Load (A) 7 SC198A Typical Characteristics (continued) VOUT vs. VIN — 3.3V Programmed Output VOUT vs. VIN — 1.8V Programmed Output 1.854 4 IOUT = 300mA 3.5 1.836 IOUT = 300mA 3 IOUT = 800mA IOUT = 800mA 1.818 Output (V) Output (V) 2.5 2 1.8 1.5 1.782 1 1.764 0.5 1.746 0 2.7 3.26 3.82 4.38 4.94 5.5 3.26 2.7 4.38 3.82 4.94 5.5 Input (V) Input (V) Crosstalk in PSAVE VIN=5.0V, 25°C, VOUTA = 1.0V, IOUTA = 80mA, VOUTB = 3.3V, IOUTB = 0mA (50mV/div) Crosstalk — Side A (PSAVE) Side B (PWM) VIN=5.0V, 25°C, VOUTA = 1.0V, IOUTA = 80mA, VOUTB = 3.3V, IOUTB = 800mA (100mV/div) (50mV/div) (100mV/div) 10μs 10μs Transient in PSAVE Transient in PWM VOUT=1.8V, VIN=3.6V, 25°C, IOUT = 0 to 800mA VOUT=1.0V, VIN=3.6V, 25°C, IOUT = 0 to 800mA (5.0mV/div) (5.0mV/div) (200mV/div) (200mV/div) (200mV/div) (200mV/div) (1.0A/div) (1.0A/div) Time (200μs/div) Time (200μs/div) 8 SC198A Typical Characteristics (continued) Switching Waveforms — VOUT=1.0V Switching Waveforms — VOUT=1.8V VIN=3.6V, 25°C, IOUT = 800mA VIN=3.6V, 25°C, IOUT = 800mA (2V/div) (2V/div) (10mV/div) (10mV/div) Time (400ns/div) Time (400ns/div) Switching Waveforms in PSAVE Switching Waveforms in PSAVE VOUT=1.8V, VIN=3.6V, 25°C, IOUT = 80mA VOUT=1.0V, VIN=3.6V, 25°C, IOUT = 0mA (2V/div) (2V/div) (10mV/div) (50mV/div) Time (20ms/div) Time (4μs/div) 9 SC198A Application Information Detailed Description The SC198A 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). 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 on-time 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 MODE/SYNC pin. When synchronizing to an external frequency, the SC198A 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. Output Filter The SC198A converter also has internal loop compensation. The internal compensation is designed to work with a specific output filter corner frequency defined by the equation fC 1 2S L u COUT When selecting output filter components, the LC product should not vary over a wide range. The practical lower limit for the inductor value is 4.7μH to ensure system stability. Selection of smaller inductor and capacitor values will shift the corner frequency higher, which may impact stability. The internal compensation is designed to operate with a single-pole output filter where L = 4.7μH and COUT = 10μF. Programmable Output Voltage The SC198A has three control pins per output to allow selection of a voltage level from eight predetermined output voltage levels (see Table 1). CAUTION — All CTL pins much be pulled high or low for proper operation (they must not be allowed to float). The output voltage can be selected while the device is enabled and loaded. Table 1 — Output Voltage Options Programmable Output Voltage CTLA2/B2 CTLA1/B1 CTLA0/B0 Nominal Output Voltage (V) A B 0 0 0 1.0 1.8 0 0 1 1.1 2.2 0 1 0 1.2 2.5 0 1 1 1.3 2.7 1 0 0 1.4 2.8 1 0 1 1.5 2.9 1 1 0 1.6 3.0 1 1 1 1.8 3.3 Continuous Conduction and Oscillator Synchronization The SC198A is designed to operate in continuous conduction mode, where it maintains a fixed frequency. When the MODE/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 MODE/SYNC pin. The part synchronizes to the rising edge of the clock. Power-Save Mode Operation The SC198A has a power-save mode (PSAVE) which may be selected by tying the MODE/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 device will automatically detect the load current at which it should enter PSAVE mode. The device is optimized to track maximum efficiency. 10 SC198A Application Information (continued) In PSAVE mode (see Figure 1), 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. When the voltage drops to the lower threshold, the switch bursts at a fixed on time until the upper threshold is reached. At this point the output voltage is allowed to ramp down to the lower threshold without switching to conserve power. In the PSAVE mode, less switching is used. This results in less power loss which can be seen in the difference of efficiency between PWM mode and PSAVE mode at light loads. PSAVE Mode at Moderate Load Upper Thershold Limit Lower Thershold Limit BURST OFF BURST Higher Load Applied PSAVE Mode at High Load BURST OFF PWM Mode at High Load PWM Mode Protection Features The SC198A provides the following protection features: • • • • Thermal Shutdown Current Limit Over-Voltage Protection Soft-Start Thermal Shutdown The SC198A has a thermal shutdown feature to protect against damage if the junction temperature exceeds 145°C. In thermal shutdown, the on-chip power devices are disabled, tri-stating the LX output. Switching resumes 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. Current Limit The internal power devices are protected by current limit functions. In the event of a short to ground on the output, the part enters frequency foldback mode. This causes the switching frequency to decrease by a factor determined by the output voltage. This prevents the inductor current from staircasing. VOUT PSAVE Exit Threshold Inductor Current 0A Time Figure 1 — PSAVE Operation The PSAVE switching burst frequency is controlled such that the inductor current ripple during the burst is similar to that in PWM mode. The SC198A 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 SC198A 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 SC198A exits PSAVE. Figure 1 shows PSAVE mode operation and exiting into PWM mode at increased load. Over-Voltage Protection In the event of an over-voltage on the output in switcher mode, the PWM drive is disabled, effectively tri-stating the LX output. The part will not resume switching until the output voltage has fallen below 2% of the regulation voltage. 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 in discrete steps. This has the desired effect of limiting in-rush current from the input supply. The softstart mode is cancelled once the output reaches regulation. Soft-start is only re-enabled by power cycling, toggling enable, a UVLO event, or shutdown. 11 SC198A Applications Information (continued) Inductor Selection The SC198A 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 is determined by the equation ǻIL VOUT § VOUT · ¨1 ¸ L u fosc © VIN ¹ 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 equation IL(Peak) IOUT(MAX) ǻIL 2 Final inductor selection will depend on various design considerations such as efficiency, EMI, size, and cost. Table 2 lists some manufacturers of practical inductor options. Table 2 — Recommended Inductors Manufacturer/ Part No. Rate Tolerance Current (+%) (A) Dimensions LxWxH (mm) Output Capacitor Output voltage ripple is dominated by the filter capacitance ESR as shown in the equation VOUT(P-P) = DIL × ESRCOUT 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. When selecting capacitors for the application, first consider the DC voltage characteristic of the capacitor. The capacitance value at the DC operating voltage may be considerably lower than the rated value. Table 3 lists recommended capacitor values which have been chosen to minimize the impact of this limitation. A 10μF ceramic capacitor is the minimum recommended value for the output filter capacitor. It is important to ensure the capacitor value does not drop below 9μF for the operating range of the application. Table 3 — Recommended Capacitors Manufacturer/ Part No. Value (μF) Rated Voltage (VDC) Type Case Size Murata GRM21BR60J226ME39 22 6.3 X5R 0805 Value (μH) DCR (Ω) Coilcraft LPO6610-472ML 4.7 0.20 1.1 ±20 6.60 × 5.50 × 1.10 Murata GRM188R60J106ME47 10 6.3 X5R 0603 Coilcraft 1812PS-472KLB 4.7 0.11 2.10 ±20 5.87 × 4.89 × 3.81 Murata GRM21BR60J106KE01B 10 6.3 X5R 0805 Coilcraft D01608C-472ML 4.7 0.09 1.5 ±20 6.60 × 4.50 × 13.0 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. 12 SC198A Applications Information (continued) 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. CinR VIN LXA CoutB LXB CoutA LA CinA GND CinB VOUTA LB GND GND GND VOUTB 13 SC198A Outline Drawing – MLPQ-20 4x4 A D B DIMENSIONS MILLIMETERS INCHES MIN NOM MAX MIN NOM MAX . 031 . 035 . 040 0. 80 0. 90 1. 00 A A 1 . 000 . 001 . 002 0. 00 0. 02 0. 05 - (0.20) - (.008) A2 b . 007 . 010 . 012 0. 18 0. 25 0. 30 D . 153 . 157 . 161 3. 90 4. 00 4. 10 D 1 . 100 . 106 . 110 2. 55 2. 70 2. 80 E . 153 . 157 . 161 3. 90 4. 00 4. 10 E1 . 100 . 106 . 110 2. 55 2. 70 2. 80 e . 020 BSC 0. 50 BSC L . 011 . 016 . 020 0. 30 0. 40 0. 50 20 20 N aaa . 004 0. 10 bbb . 004 0. 10 DIM PIN 1 INDICATOR (LASER MARK ) E A2 A 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 14 SC198A Land Pattern – MLPQ-20 4x4 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 Mangement Products Division 200 Flynn Road, Camarillo, CA 93012 Phone: (805) 498-2111 Fax: (805) 498-3804 www.semtech.com 15