SEMTECH SC4508

SC4508 Buck or Buck-Boost(Inverting) Current Mode Controller POWER MANAGEMENT Features Description The SC4508 is a low voltage current mode switching regu- ‹ Wide input voltage range 2.7V to 15V lator controller that drives a P-channel power MOSFET ‹ Programmable output voltage with programmable switching frequency. It can be con- ‹ Programmable switching frequency up to 1.5MHz figured in either buck or buck boost (inverting) convert- ‹ Buck or buck boost(inverting) configuration ers. The converters can be operated from 2.7V to 15V ‹ Current mode control with slope compensation input voltage range. The typical operating supply current ‹ Very low quiescent current in shutdown mode is 3mA and a shutdown pin allows the user to turn the ‹ Accessible reference voltage controller off reducing it to less than 200µA. The output ‹ MLPQ-12 package voltage can adjusted by external resistor divider. The switching frequency is programmable up to 1.5MHz, Applications allowing small inductor and capacitor values to minimize PCB space. The operating current level is programmable ‹ Low power point of use converters via an external sense resistor. Accessible reference volt- ‹ Single or multiple output low power converters age allows users to make output voltage as low as they ‹ Positive and/or negative output voltage want. ‹ DSL cards ‹ Graphic cards ‹ I/O cards ‹ Negative bias supplies Typical Application Circuits Vin Vin VDD VDD VREF VREF FB+ CS SC4508 FB- CS FB+ SC4508 OUT FB- COMP OUT COMP SS/SHDN GND OSC SS/SHDN GND OSC 1 www.semtech.com Revision: November 30, 2004 SC4508 POWER MANAGEMENT Absolute Maximum Rating 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. Exposure to Absolute Maximum rated conditions for extended periods of time may affect device reliability. Pl arameter Sm ymbo Ms aximu Unit VDD to GND -V 0.3 to 16 SS/SHDN to GND 3V .2 FB+, FB-, COMP, OSC to GND 5V VREF Current 1A m OUT Source or Sink 2A 50 m Thermal Resistance, Junction to Ambient 4W 8 °C/ θ JA Thermal Resistance, Junction to Case θ 3W °C/ JC ST torage Temperature Range -C 60 to +150 ° STG JT unction Temperature Range -C 40 to +150 ° J PT eak IR Reflow Temperature 10 - 40s 2C 60 ° PKG Electrical Characteristics Unless specified: V = 2.7V to 15V , T = T = -40°C to 125°C DD A J Ps arameter Tn estCondition Mp i Tx y Mt a Uni PowerSupply Input Voltage Range 25 .7 1V Qw uiescent Current S0 HDN = lo 20 0 5A 0 µ Od perating CurrentS3 HDN = high, No loa mA Undervoltage Lockout SV tart Threshold r5 ising 25 . 2V .5 DD UVLO Hysteresis 1V 00 m Oscillator Frequency Range 10 00 1z 50 KH FC requency =0 300pF 40 5 50 0 5z 5 KH T Charge Current 1A 00 µ ErrorAmplifier Feedback Input Voltage 0V .75 Input Bias Current 1A 00 n Transconductance 5S m Output Source or Sink Current 50 01A 0 µ www.semtech.com  2004 Semtech Corp. 2 SC4508 POWER MANAGEMENT Electrical Characteristics Unless specified: V = 2.7V to 15V , T = T = -40°C to 125°C DD A J Ps arameter Tn estCondition Mp i Tx y Mt a Uni PWMComparator Delay to Output 5s 0 n VREF Reference Output Voltage 15 .231 19 .2 1V .26 Output Current 1A m LV ine Regulation = 2.7 to 15V, I=4 1mA mV DD VREF LV oad Regulation = 5V, I=4 0 to 1mA mV DD VREF SoftStart/Shutdown Charge Current 2A 0 µ Discharge Current 1A 2 m SHDN Logic Hight Voltage 2V SHDN Logic Low Voltage 0V .25 CurrentLimit CV ycle by Cycle Threshold =0 5V 9010 1 1V 3 m DD Shutdown Threshold 0V .16 Delay to Output 5S 0 n Output GV ate Drive On-Resistance(H) = 5V, I=0 250mA 2m Oh DD SOURCING GV ate Drive On-Resistance(L) = 5V, I=0 250mA 2m Oh DD SINK RC ise Time =0 200pF 2S n OUT FC all Time =0 200pF 2S n OUT Note: (1) This device is ESD sensitive. Use of standard ESD handling precautions is required.  2004 Semtech Corp. 3 www.semtech.com SC4508 POWER MANAGEMENT Pin Configuration Ordering Information DE EVICE PT ACKAG Temp.Range ( ) J TOP VIEW (2) (1) SC4508IMLTRT MLPQ-12 -40°C to 150°C VDD OSC COMP Notes: (1) Only available in tape and reel packaging. A reel contains 3000 devices. 12 11 10 (2) Lead free product. This product is fully WEEE and OUT 1 9 FB+ RoHS compliant. CS 2 8 FB- SS/SHDN 3 7 PGND 4 5 6 VREF NC AGND (MLPQ-12 4x4) Pin Descriptions Pe in # Pn in Nam Pin Functio 1T OU Gate driver output for external P-MOSFET. OUT swings from VDD to PGND. 2S C Current sense input pin. Connect a current sense resistor between VDD and CS. 3N SS/SHD Soft start pin. Connects an external capacitor between this pin and AGND. The ramp up time is defined by the capacitor. The device goes into shutdown when VSS/SHDN is pulled below 0.25V. 4F VRE 1.25V reference output. VREF can source up to 1mA. Bypass with a 0.1uF ceramic capacitor from VREF to AGND. 5CN. No connection 6DA. GN Analog ground 7DP. GN Power ground 8-F. B Error amplifier inverting input 9+F. B Error amplifier non-inverting input 1P 0 COM Compensation pin for the internal transconductance error amplifier. Connect loop compensation network from COMP to AGND. 1C 1 OS Oscillator frequency set input. Connect a ceramic capacitor from OSC to AGND to set the internal oscillator frequency from 100KHz to 1.5MHz. Use equation to set the 100µA f = oscillator frequency. C is the capacitor from OSC to AGND. C • 0.65 1D 2 VD Supply voltage. Bypass a 1uF ceramic capacitor from VDD to PGND. -L THERMA Pad for heatsinking purposes. Connect to ground plane using multiple vias. Not connected PAD internally. www.semtech.com  2004 Semtech Corp. 4 SC4508 POWER MANAGEMENT Block Diagram Marking Information Top View yyww = Date Code (Example: 0012)  2004 Semtech Corp. 5 www.semtech.com SC4508 POWER MANAGEMENT Application Information Inductor Selection The SC4508 is designed to control buck (step down) or buck-boost (inverting) converter with P-channel MOSFET A inductor is chosen based on the required output ripple current which is usually 20-30% of load current. The ripple as a switch using current mode, programmable switching frequency architecture. During steady state operation, current ΔI decreases with higher inductance and the switch is turned on each cycle and turned off when increases with higher input voltage V or output voltage IN the voltage across current sense resistor exceeds the V O. voltage level at COMP pin set by voltage loop error amplifier. A fixed 0.5V artificial ramp is added internally V − V V + V IN O O D to the sensed current signal for operations when duty- L = ( ) for Buck f • ΔI V + V s L IN D cycle is larger than 50%. In over load or output shortage condition, if the sensed current signal reaching typical 120mV, the switch is turned off immediately in the same V + V V O D IN for Buck-Boost cycle. If the sensed current signal further increases to L = ( ) f • ΔI V + V + V s L IN O D typical 160mV, not only the switch is turned off but also the soft start capacitor is discharged by a internal MOSFET Specify the maximum inductor current larger than I (pk) to ground then charging back to threshold 250mV during L set by the current sense resistor R to avoid the inductor which the switch is held off. With the “hiccup” mode over S core saturation. current protection, the thermal stress is reduced in the faulty conditions. Input Capacitor C and Output Capacitor C Selection IN OUT Current Sense and Current Limit Both input and output capacitors need to be sized to handle the ripple current safely. Buck converters have The typical cycle-by-cycle current limit threshold in the high ripple current in the input side while buck-boost current sense pin of the SC4508 is 120mV. The over converters have high ripple current in the both input and current limit is assumed typical 120% of full load current. output capacitors. Therefore, the RMS value of the Then the current sense resistor can be calculated by the current must be less than the high frequency ripple rating following equation: of the capacitors. In continuous mode operation, 120mV Rs = 120% •I (pk) L V (V − V ) O IN O I ≈ I RMS _INPUT _ CAP O for Buck V IN 1 V − V V + V IN O O D I + ( ) I (pk) = O for Buck L 2 f •L V + V s IN D V + V O D I ≈ I RMS _ CAP O for Buck-Boost input and output V IN V + V + V V + V 1 V IN O D O D IN capacitors. I (pk) I ( = + ) L O V 2 f •L V + V + V IN s IN O D The C is selected for Buck converter is by required for Buck − Boost OUT output ripple voltage and converter loop stability. The output ripple is determined by: I - full load current O V - output voltage 1 O ΔV ≈ ΔI (ESR + ) O L V - input voltage IN 8f C s OUT V - diode forward voltage drop D f - switching frequency S where f is converted switching frequency, C is output L - inductor S OUT capacitance and ΔI is inductor ripple current. L www.semtech.com  2004 Semtech Corp. 6 SC4508 POWER MANAGEMENT LAYOUT GUIDELINES Application Information (Cont.) In Buck converter, the worst case input RMS ripple current Careful attention to layout requirements are necessary occurs at 50% duty cycle, or at V = 2V . Under this for successful implementation of the SC4508 PWM con- IN OUT condition, the input capacitors RMS ripple current is about troller. High switching currents are present in the appli- half of the load current. cation and their effect on ground plane voltage differen- tials must be understood and minimized. MOSFET Selection 1). The high power parts of the circuit should be laid out The selection criteria for the power MOSFET is its first. A ground plane should be used, the number and operating junction temperature not exceeding the position of ground plane interruptions should be such as maximum junction temperature. Therefore, from a to not unnecessarily compromise ground plane integrity. specified ambient temperature, the maximum junction Isolated or semi-isolated areas of the ground plane may to ambient temperature rise has to be determined, which be deliberately introduced to constrain ground currents is related to the MOSFET power dissipation or power loss. to particular areas, for example, the input capacitor and The power loss includes conduction loss and switching output capacitor ground. loss. The conduction loss is given by: 2). The loop formed by the Input Capacitor(s) (Cin), the MOSFET and the Schottky diode or inductor must be kept V + V O D 2 P = ( )I R ON O DS(ON) for Buck as small as possible. This loop contains all the high cur- V + V IN D rent, fast transition switching. Connections should be as wide and as short as possible to minimize loop induc- tance V + V + V IN O D 2 P = ( )( V + V )I R ON O D O DS(ON) for Buck-Boost V IN 3). The connection between the junction of MOSFET, Schottky diode and the output inductor should be a wide Freewheeling Diode Selection trace or copper region. It should be as short as practical. Since this connection has fast voltage transitions, keep- The Schottky diode is recommended as freewheeling ing this connection short will minimize EMI. diode in the both Buck and Buck-Boost applications. The diode conducts during the off-time. The diode voltage 4) The Output Capacitor(s) (Cout) should be located as and current ratings are selected based upon the peak close to the load as possible, fast transient load cur- reverse voltage, the peak current and average power rents are supplied by Cout only, and connections between dissipation. Cout and the load must be short, wide copper areas to minimize inductance and resistance. ΔI V − V L IN O V = V , I = I + ,I = I for Buck D(REV) IN D(PEAK ) O D(AVG) O 2 V + V 5) A separate analog ground plane connects to the IN D SC4508 AGND pin. All analog grounding path including decoupling capacitors, feedback resistors, compensation V + V + V ΔI IN O D L components, and current-limit setting resistors should V = V + V , I = I ( ) + ,I = I D(REV) IN O D(PEAK) O D(AVG) O V 2 be connected to this plane. IN for Buck − Boost The most stressful condition for the diode occurs when the output is shorted. Under this condition, due to the V = 0, the diode conducts at close to 100% duty cycle. OUT Therefore, attention should be paid to the thermal condition when laying out a board.  2004 Semtech Corp. 7 www.semtech.com SC4508 POWER MANAGEMENT Evaluation Board Schematic, Buck 12V GND C1 C2 R7 U1 R1 U1 47uF/16V 47uF/16V 10K C3 0.09 SC4508 1nF C4 R2 10 TP1 1uF 12 2 VDD CS U2 FDFS2P102A 3 1 4 5 SS/SHDN OUT C5 11 4 3 6 OSC VREF TP3 0.1uF TP2 L1 C7 C6 5 9 2 7 0.1uF 10uH NC FB+ 330pF 6V/1A 6 8 1 8 AGND FB- fs=440KHz TP4 7 10 C8 C9 PGND COMP 470uF/6.3V 470uF/6.3V R4 20K C10 GND 2nF C11 R5 2.7nF 3.74K R6 TP5 1.24K TP6 TP7 TP8 Bill of Materials Iy tem Qe uantit Rt eferenc Pr ar Manufacture 12CV 1,C2 4M 7uF/16 Sanyo P/N: 16TPB47 21CF 3 1n 31CF 4, 1u 42CF 5,C7 0.1u 51CF 6 330p 62CV 8,C9 4M 70uF/6.3 Sanyo P/N: 16TPB470 71CF 10 2n 81CF 11 2.7n 91LH 1 10u 11 0R9 1 0.0 11 1R0 2 1 11 2RK 4 20 11 3RK 5 4.75 11 4RK 6 1.24 11 5RK 7 10 11 6U8 1 S. C450 Semtech Corp 11 7UA 2 F: DFS2P102FA airchild P/N FDFS2P102 www.semtech.com  2004 Semtech Corp. 8 SC4508 POWER MANAGEMENT Evaluation Board Schematic, Buck-Boost TP9 12V GND R7 C1 C2 R1 U1 10K U1 47uF/16V 47uF/16V C3 0.1 SC4508 1nF C4 R2 100 TP1 TP10 1uF 12 2 VDD CS U2 Si4831DY 3 1 4 5 SS/SHDN OUT C5 TP3 11 4 3 6 OSC VREF 0.1uF C6 R8 5 9 2 7 C7 NC FB+ 680pF 249 0.1uF 6 8 1 8 AGND FB- fs=250KH z L1 R9 1.0K TP4 7 10 33uH PGND COMP R4 20K C10 -5V/0.1A 100pF C8 D1 C9 C11 47uF/16V 100uF/6.3V 1N5819HW 2.7nF R5 6.04K R6 240 GND TP5 TP6 TP7 TP8 Bill of Materials Iy tem Qe uantit Rt eferenc Pr ar Manufacture 13CV 1,C2,C8 4M 7uF/16 Sanyo P/N: 16TPB47 21CF 3 1n 31CF 4 1u 42CF 5, C7 0.1u 51CF 6 680p 61CV 9 100uF/6.3 71CF 10 100p 81CF 11 2.7n 91DW 6 1N5819H 11 0LH 1 3.3u 11 1R1 1 0. 11 2R0 2 10 11 3RK 4 20 11 4RK 5 6.04 12 5R9 6, R8 24 11 6RK 7 10 11 7RK 9 1.0 11 9U8 1 S. C450 Semtech Corp 21 0UY 2 Sy i4831D Visha  2004 Semtech Corp. 9 www.semtech.com SC4508 POWER MANAGEMENT Outline Drawing - MLPQ-12, 4 x 4 DIMENSIONS INCHES MILLIMETERS DIM MIN NOM MAX MIN NOM MAX A D B - - A .031 .040 0.80 1.00 - - A1 .000 .002 0.00 0.05 A2 - (.008) - - (0.20) - b .010 .012 .014 0.25 0.30 0.35 PIN 1 D .153 .157 .161 3.90 4.00 4.10 INDICATOR E D1 .074 .085 .089 1.90 2.15 2.25 (LASER MARK) E .153 .157 .161 3.90 4.00 4.10 E1 .074 .085 .089 1.90 2.15 2.25 e .031 BSC 0.80 BSC L .018 .022 .026 0.45 0.55 0.65 N 12 12 aaa .003 0.08 bbb .004 0.10 A2 A SEATING PLANE aaa C C A1 D1 LxN E/2 2 E1 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. Land Pattern - MLPQ-12, 4 x 4 K DIMENSIONS INCHES MILLIMETERS DIM (.148) (3.75) C G .106 2.70 2x Z H 2x G 2x (C) H .091 2.30 K .091 2.30 P .031 0.80 X .016 0.40 Y Y .041 1.05 Z .189 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  2004 Semtech Corp. 10