SC192 Synchronous Buck Converter with Integrated Power Devices POWER MANAGEMENT Description Features 2.7V to 7V Input Range Output Adjustable from 0.75V to Vin Fixed Frequency or PSAVE for Maximum The SC192 is a synchronous step-down converter with integrated power devices designed for battery operated systems. The internal power switches reduce system size and cost. In addition, an efficiency of 95% can be achieved for significant line and load ranges. The SC192 is designed for single-cell Li-Ion battery applications, but also performs well in fixed 3.3V or 5V input circuits. The SC192 has a flexible clocking scheme. It can be synchronized to an external oscillator, fixed to the inter- nal oscillator, or allowed to modulate the frequency dur- ing light loads (PSAVE) for maximum battery life, by the method called pulse frequency modulation (PFM). Shutdown places the switches in a high impedance state and turns off all control circuitry to achieve a typical quiescent current of 0.1μA. Efficiency Over Wide Load Current Range 700mA Guaranteed Output Current No Schottky Diode Required 35μA Quiescent Current 100% Duty Cycle in Dropout 95% Efficiency Fast Transient Response Over Temperature Protection Space-saving Micro Lead-Frame Package MLPD-10 3x3 Applications Line and load regulation is to +/-0.5% of the output voltage. The internal MOSFET switches provide >1A peak current to provide a DC output of at least 700mA. Grounding the ILIM pin reduces the current limit by half. Cell Phones Cordless Phones Notebook and Subnotebook Computers PDAs and Mobile Communicators 1 Li-Ion or 3 NiMH/NiCd Powered Devices The SC192 can achieve 100% duty cycle for excellent low dropout performance and comes in a tiny MLPD-10, 3 x 3 package having a maximum height of 1mm. Typical Application Circuit SC192 L1 Vin = 2.7V to 7V 1 C1 8 VIN C5 EN R1 5 ADJ 6 Vout = 0.75V to Vin 9 LX C6 ILIM R2 PGND 2 BP 10 7 SYNC/PWM C3 3 Revision 8, March 26, 2007 GND 4 COMP 1 R8 C4 www.semtech.com SC192 POWER MANAGEMENT Absolute Maximum Ratings PRELIMINARY 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 Symbol Maximum Units V IN -0.3toto7.5 7 -0.3 V VSYNC -0.3toto7.5 7 -0.3 V V EN -0.3toto7.5 7 -0.3 V VPGDN -0.3 to 0.3 V LX Voltage V LX -1 to VIN +1 V ILIM Voltage V IL IM -0.3 to VIN + 0.3 V ADJ Voltage VADJ -0.3 to VIN + 0.3 V VCOMP -0.3 to VIN + 0.3 V BP Voltage V BP VIN - 0.3 to VIN + 0.3 V Thermal Impedance Junction to Ambient θJA *57 Output Shor t Circuit to GN D tSC Continuous s LX Current IL X +1.6 A T LE A D 240 260 ° TS -65 to +160 ° V IN i n p u t SYN C/PWM Input E N In p u t PGN D to GN D COMP Voltage Peak IR Reflow Temperature SC192IMLTR (Soldering) 10s - 30s SC192IMLTRT (Soldering) 20s - 40s Storage Temperature C/W ° C C * Tied to PCB with 1 square inch, 2 ounce copper. Note: This device is ESD sensitive. Use of ESD handling precautions is required. Electrical Characteristics Unless otherwise noted: VIN = 3.6V, SYNC/PWM = VIN, ILIM = VIN, EN = VIN, TA =-40 to 85°C. Typical values are at TA = +25°C. Parameter Symbol Conditions Min Typ Max Units 57.5 V VIN 2.7 ADJ Regulation Voltage V AD J 0.731 0.75 0.769 V ADJ Input Current IADJ -50 0 50 nA Output Voltage Adjust Range VOUT V AD J VIN V Line Regulation REGLINE -0.5 +0.5 % Load Regulation(1) REGLOAD Peak Inductor Current = 0 to 700mA 0 0.6 % P-Channel On Resistance RDSP ILX = 200mA 0.3 Ω N-Channel On Resistance RDSN ILX = 200mA 0.4 Ω Input Voltage Range © 2007 Semtech Corp. ADJ = 0.75V 2 www.semtech.com SC192 POWER MANAGEMENT Electrical Characteristics Cont. Unless otherwise noted: VIN = 3.6V, SYNC/PWM = VIN, ILIM = VIN, EN = VIN, TA =-40 to 85°C. Typical values are at TA = +25°C. Parameter P-Channel Current Limit N -Channel Current Limit Symbol Conditions Min Typ Ma x Units I L IM ( P ) ILIM = GN D 420 600 780 mA I L I M = V IN 840 1200 1560 mA SYN C/PWM = GN D, PSAVE Mode 45 105 165 mA -320 -420 -520 mA 35 50 μA I L IM ( N ) Quiescent current IQ SYN C/PWM = GN D, PSAVE Mode Shutdown Current ISD EN = 0, LX = Open, TA = 25°C 1 μA LX leakage Current PMOS ILXP VIN = 5.5V, LX = 0V, EN = 0V 1 μA LX leakage Current N MOS ILXN VIN = 5.5V, LX = 5.5V, EN = 0V Oscillator Frequency fOSC 650 SYN C Frequency Range fSYNC Duty Cycle Range D UVLO Threshold V UV L UVLO Hysteresis VUVLHYS SYN C/PWM = GN D, PSAVE Mode -20 μA 830 kHz 500 1000 kHz 20 100 % 2.65 V 2.35 750 2.5 50 Thermal Shutdown mV C 160 Logic Input High V IH EN , SYN C/PWM, ILIM Logic Input Low V IL EN , SYN C/PWM, ILIM Logic Input Current High I IH EN , SYN C/PWM, ILIM Logic Input Current Low I IL EN , SYN C/PWM, ILIM ° 2 V 0.8 V -2 2 μA -2 2 μA Notes: (1) Load regulation limits are specified from 0 to 700mA. This specification is calculated based on parameters measured individually and is not a tested parameter. See the load regulation limit graph on page 13 for more detailed view of performance. © 2007 Semtech Corp. 3 www.semtech.com SC192 POWER MANAGEMENT Pin Configuration PRELIMINARY Ordering Information DEVICE(1) PACKAGE SC192IMLTR TOP VIEW VIN 1 BP 2 9 LX GND 3 8 EN COMP 4 ADJ 5 10 PGND T MLPD-10 3x3 SC192IMLTRT(2) SC192EVB Evaluation Board Note: (1) Only available in tape and reel packaging. A reel contains 3000 devices. (2) Lead free product. This product is fully WEEE and RoHS compliant. 7 SYNC/PWM 6 ILIM MLPD-10: 3X3 10 LEAD Pin Descriptions Pin # Pin Name Pin Function 1 V IN Input power supply voltage; this input goes directly to the internal MOSFET switches. 2 BP Bypass capacitor pin; an external capacitor combined with an internal resistor provides a filtered supply voltage for the internal control circuitry. Connect a 0.1uF capacitor from BP to ground. 3 GN D 4 COMP 5 ADJ Output adjust pin; connect to a resistor divider to set the output voltage. 6 I L IM Digital current limit select input. Connect ILIM to GN D for 0.6A current; connect ILIM to VIN for 1.2A current limit. 7 SYN C/PWM 8 EN Enable digital input; a high input enables the SC192 a low disables the device and reduces quiescent current to 0.1uA. In shutdown, LX becomes high impedance. 9 LX Inductor connection to the switching FETs. 10 PGN D T Thermal Pad © 2007 Semtech Corp. Analog ground. Compensation pin for the error amplifier. Oscillator synchronization input. Tie to VIN for forced PWM mode, GN D to enable power save mode, or an external clock signal for frequency synchronization. Power Ground. Pad for heatsinking purposes. Connect to ground plane using multiple vias. N ot connected internally. 4 www.semtech.com SC192 POWER MANAGEMENT Block Diagram VIN BP - ILIM V Plimit amp + + SYNC/ PWM - Current amp OSC and slope generation - COMP Control logic LX PWM comp + PGND ADJ Error amp + V 750mV + - Nlimit comp EN GND © 2007 Semtech Corp. 5 www.semtech.com SC192 POWER MANAGEMENT Description PRELIMINARY Forced PWM If SYNC/PWM is DC high, the forced PWM mode is enabled. This ensures that the switching frequency of the converter is maintained over the full range of output loads. This means that the current reversal threshold of the NMOS is changed to a negative value and the 100% duty cycle and power save modes are also disabled. Description The SC192 step-down, pulse-width-modulated (PWM), DC-DC converter has an adjustable output range from 0.75V to the input voltage. The device has an internal synchronous rectifier and does not require a schottky diode on the LX pin. At moderate to heavy loads, the converter operates in the PWM mode with a fixed frequency of 750kHz. At light loads the converter enters the power save mode by modulating the frequency, pulse-frequency-modulation (PFM) which achieves high efficiency under light load conditions. 100% Duty-Cycle Operation Normally the control loop constrains the duty cycle of the converter with minimum on and off times, but if the output voltage droops to the lower power-save threshold and the ON time is not terminated by the PWM comparator or PMOS current limit, then the next PMOS on time is allowed to extend until either the PWM comparator or PMOS current limit trips. This is then followed by a minimum off time. This maximum on time/minimum off time is allowed to continue until the upper power-save threshold is reached. This allows the part to go into a dropout mode of operation if the input supply collapses down to the output voltage. If this happens, the output voltage is equal to the input voltage minus the voltage drop across the P-channel MOSFET. Normal Mode This is a standard fixed frequency current mode topology. The current feedback is through the PMOS current path and is amplified and summed with the internal slope compensation network and DC offset. The voltage feedback loop is through the resistor divider attached to the ADJ pin. The transconductance error amplifier output is the compensation (COMP) pin with the usual external compensation network attached. The PWM COMP pin closes the loop by comparing the summed current feedback and the COMP signal to determine the length of the ON time. The period is set by the on-board oscillator or external clock attached to the SYNC pin. Soft Start The soft start mode is enabled after every shutdown cycle to limit inrush current from the battery. In conjunction with the frequency foldback this controls the maximum current during start-up. The PMOS current limit is stepped from 25%, to 50%, to 75%, and then 100% by an internal 2ms timer. As soon as the part reaches regulation, soft start mode is disabled. Power Save Mode If SYNC/PWM is DC low, power save mode is used at light loads to improve efficiency. When the output current reaches a low enough level, the part goes into a voltage hysteresis mode of operation. The current level for this is set to be the current reversal protection on the NMOS device. The output voltage is then allowed to decay to a lower threshold with the part in a reduced quiescent current (PSAVE) state. After this lower threshold is reached the part is reawoken to normal operation, but with a current offset on the COMP pin to drive the output voltage regulation point to be above an upper threshold point. However the offset is removed once the upper threshold is reached. If the load current is now sufficiently large the part will return to normal regulation, if not another PSAVE cycle will start. Frequency Foldback When the ADJ pin is low the output switching frequency is folded back in several discrete steps to protect against a short to GND on the output and improve inrush current control during start-up. © 2007 Semtech Corp. 6 www.semtech.com SC192 POWER MANAGEMENT Evaluation Board Schematic VIN R7 1k TP7 EN R5 100k 6 5 4 R6 1k SW1 DIP 1 2 3 TP8 ILIM TP1 VIN TP4 LX U1 1 VIN 2 TP3 COMP 3 4 5 C1 10uF C3 0.1uF C4 470pF VIN BP PGND LX GND EN COMP SY NC ADJ ILIM TP5 VOUT 10 L1 9 1.8V 10uH 8 7 C5 47pF R1 442k 6 EN SC192 R2 309k R8 28k C2 0.1uF C6 22uF TP6 SYNC SY NC R3 100k TP2 GND R4 100k GND © 2007 Semtech Corp. 7 www.semtech.com SC192 POWER MANAGEMENT PRELIMINARY Evaluation Board Gerber Plots © 2007 Semtech Corp. TOP COPPER BOTTOM COPPER TOP SILKSCREEN BOTTOM SILKSCREEN 8 www.semtech.com SC192 POWER MANAGEMENT Applications Information Selecting Components When selecting components for the an SC192 application the main factors are typically performance, size and cost. For higher performance the designer will select higher values of input and output capacitors to reduce ripple current and voltage. However, for an application that can tolerate higher ripple, less expensive and smaller components can be utilized. The schematics below show two possibilities. The first shows the use of 10μF capacitors on the input and output with L1 = 10μH, while the second shows the use of smaller less expensive 4.7μF capacitors and L1 = 4.7μH. The only circuit consideration for choosing one over the other is the compensation components C4 & R8. When these components are in place the values of R2 can be chosen for a given output voltage. The values that should be used are indicated in Table 1 below. Using a different value for R1 is not advised since this will change the loop characteristics and may cause the supply to become unstable. Any output voltage is achievable using R1 of 442k and then selecting R2 to achieve the desired output voltage. The equation for VOUT is: ⎛ R1 ⎞ Vout = ⎜ + 1⎟ • 0.75 ⎝ R2 ⎠ Because the SC192 has external compensation the use of small inexpensive ceramic capacitors can be used for the output capacitor allowing the designer greater flexibility. 1 VIN 2 3 4 5 C1 10uF C3 0.1uF VIN BP PGND LX GND EN COMP SY NC ADJ C4 470pF ILIM 10 L1 9 VOUT 10uH 8 7 C5 47pF R1 442k 6 C6 10uF SC192 R2 R8 12k 1 VIN 2 3 4 5 C1 4.7uF C3 0.1uF C4 470pF VIN BP PGND LX GND EN COMP SY NC ADJ ILIM 10 L1 9 VOUT 4.7uH 8 7 C5 47pF R1 442k 6 C6 4.7uF SC192 R2 R8 6.19k © 2007 Semtech Corp. 9 www.semtech.com SC192 POWER MANAGEMENT Applications Information Cont. PRELIMINARY TABLE 1 VOUT R2 R2 3.3V 130k 2.5V 187k 1.8V 309k 1.5V 442k 1.0V 1.30M C6 = Cout = 10uF L1 = 10uH C6 = Cout = 22uF L1 = 10uH C6 = Cout = 4.7uF L1 = 4.7uH C4 = 470pF R8 = 12k C4 = 470pF R8 = 28k C4 = 470pF R8 = 6.19k The plots below were taken at Vin = 3.6V, Vout = 1.8V, with the compensation components listed in Table 1. The upper plot is LX, the middle plot is output voltage, the lower plot is the current transient of 0.1A to 0.6A PSAVE, Cout = 20uF, Lout = 10uH PWM, Cout = 20uF, Lout = 10uH PSAVE, Cout = 10uF, Lout = 10uH © 2007 Semtech Corp. PWM, Cout = 10uF, Lout = 10uH 10 www.semtech.com SC192 POWER MANAGEMENT Applications Information Cont. PSAVE, Cout = 4.7uF, Lout = 4.7uH PWM, Cout = 4.7uF, Lout = 4.7uH Inductor Selection The inductor values listed in Table 1 will work for nearly all combinations of output current and output voltages. After selecting 4.7uH or 10uH for the inductor value two additional inductor parameters should be considered. The current rating of the inductor and the DC resistance. The DC resistance has a great impact on efficiency due to copper losses. However, small inductors tend to have higher DC resistance. Therefore a compromise between size and efficiency will need to be made. The inductor current must be chosen to prevent the inductor from saturation. The most conservative approach would be to select an inductor with a saturation current slightly above the maximum current capability of the SC192 which is 1.56A peak current for ILIM = Vin or 780mA for ILIM = GND. A more accurate design of the inductor would be to rate the inductor for the maximum output current plus the inductor ripple current that can be calculated as follows: IL(MAX) = IO(MAX ) + f = Switching frequency L = Inductor Value ΔIL= Peak-to-peak inductor ripple current IL = Maximum inductor current VOUT = Output voltage VIN = Input voltage COUT = Output Capacitance IOUT = Output Current IOUT(MAX) = Maximum DC Output Current Output Capacitor Selection Because the SC192 has external compensation available, low ESR ceramic capacitors can be used. This eliminates the need for bulky tantalum capacitors. Values for the output capacitors in Table 1 will work for nearly all combinations of output current and output voltages. The equation for determining the size of the output capacitor in terms of minimizing the ripple voltage is given as follows: ΔIL 2 1 ⎞ ⎛ ΔVO = ΔIL • ⎜ + ESR ⎟ ⎠ ⎝ 8 • COUT • f ⎛ VOUT ⎞ ⎜ 1⎟ ΔIL = ⎜ VIN ⎟ • VOUT ⎜ L• f ⎟ ⎜ ⎟ ⎝ ⎠ © 2007 Semtech Corp. Input Capacitor Selection The input ripple current can be reduced with properly selecting the input capacitor. Again, values for the input capacitors in Table 1 will work for nearly all combinations of input current and output voltages. The input capacitor should be rated for the maximum input ripple current calculated as: 11 www.semtech.com SC192 POWER MANAGEMENT Applications Information Cont. Load Regulation at Vin = 3.6V 0.45 IOUT VIN 0.40 Load Regulation (%) IRMS = VOUT • VIN - VOUT • PRELIMINARY The worst case RMS ripple current occurs at a duty cycle of 0.5 and its value at that point is IOUT . 2 0.35 0.30 0.25 Vo = 1.8V 0.20 Vo = 2.5V 0.15 0.10 0.05 0.00 Ceramic capacitors are recommended for input capacitors because of their low ESR and high ripple current capabilities. In addition, it is advised that the input capacitor be placed as close to the input pin of the IC as possible. 1 20 40 60 80 100 200 300 400 500 600 Ouput Current (mA) Efficiency at Vin = 5V Efficiency (%) Layout Considerations PCB layout is of utmost importance because the switching frequency is 750kHz with peak currents over 1A. A careful layout will avoid potential stability and EMI problems. Traces should be as wide and as short as possible. Keep the input capacitor as close to the package as possible. This will help minimize large loop areas. Keep the power ground and analog ground separated and tie the two together at one common point. Notice the top copper Gerber plot (see Page 8), pin 3 and pin 10 are tied together under the package. Be aware of the high current paths and avoid tying signal grounds to the high power grounds where the signal paths might experience large fluctuations in voltages as high currents pass though copper traces. 100 95 90 85 80 75 70 65 60 Vo = 3.3V 1 10 30 50 70 90 200 400 600 Load Current (mA) Efficiency at Vin = 3.6V Efficiency (%) 100 95 Vo = 2.5V 90 Vo = 1.8V 85 80 1 10 30 50 70 90 200 400 600 Load Current (mA) Line Regulation At Iout = 300mA Line Regulation (%) 0.10 0.08 0.06 Vo = 1.8V 0.04 0.02 0.00 2.7 3.0 3.3 3.6 3.9 4.2 4.5 4.8 Input Voltage (Volts) © 2007 Semtech Corp. 12 www.semtech.com SC192 POWER MANAGEMENT Line Regulation at IOUT = 300mA SC192 Load Regulation Limits 1.0 0.14 Load Regulation (%) Line Regulation (%) 0.9 0.12 0.10 0.08 Vo = 2.5V 0.06 0.04 0.02 0.8 0.7 0.6 0.5 0.4 0.3 Load Reg Max Load Reg Typ Load Reg Min 0.2 0.1 0.00 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 0.0 4.9 0 0.2 Input Voltage (Volts) 0.4 0.6 0.8 1 1.2 Peak Inductor Current (Amps) Oscillator Frequency vs Temperature Over VIN Oscillator Frequency vs VIN Over Temperature 760 760 755 755 Vin = 2.7 V Vin = 3.6V Vin = 5.5V 745 740 750 Fosc (kHz) Fosc (kHz) 750 735 730 745 735 730 725 725 720 720 715 715 710 Temp = -40C Temp = 0C Temp = 25C Temp = 85C Temp = 125C 740 710 -60 -40 -20 0 20 40 60 80 100 120 140 2 Temp (OC) 2.5 3 3.5 4 4.5 5 5.5 6 Vin (Volts) Shutdown Current vs Temperature Shutdown Current (µA) 0.9 0.8 0.7 0.6 0.5 Vin = 3.6V 0.4 0.3 0.2 0.1 0 -40 0 25 85 125 O Temperature ( C) © 2007 Semtech Corp. 13 www.semtech.com SC192 POWER MANAGEMENT Outline Drawing - MLPD-10, 3 x 3 A PRELIMINARY E DIMENSIONS INCHES MILLIMETERS DIM MIN NOM MAX MIN NOM MAX B A A1 A2 b C D E e L N aaa bbb E PIN 1 INDICATOR (LASER MARK) .031 .039 .000 .002 (.008) .007 .009 .011 .074 .079 .083 .042 .048 .052 .114 .118 .122 .020 BSC .012 .016 .020 10 .003 .004 0.80 1.00 0.00 0.05 (0.20) 0.18 0.23 0.30 1.87 2.02 2.12 1.06 1.21 1.31 2.90 3.00 3.10 0.50 BSC 0.30 0.40 0.50 10 0.08 0.10 A SEATING PLANE aaa C A1 C 1 C A2 2 LxN D N e bxN bbb C A B NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS TERMINALS. Marking Information Top Marking 192 yyww yy = two-digit year of manufacture ww = two-digit week of manufacture © 2007 Semtech Corp. 14 www.semtech.com SC192 POWER MANAGEMENT Land Pattern - MLPD-10, 3 x 3 K DIM (C) H G Y X Z C G H K P X Y Z DIMENSIONS INCHES MILLIMETERS (.112) .075 .055 .087 .020 .012 .037 .150 (2.85) 1.90 1.40 2.20 0.50 0.30 0.95 3.80 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 Visit us at: www.semtech.com © 2007 Semtech Corp. 15 www.semtech.com