SS6638-33GZTR

SS6638G Simple 3-Pin Step-Up DC/DC Converter FEATURES Guaranteed start-up from less than 0.9 V. High efficiency. Low quiescent current. Fewer external components needed. Low ripple and low noise. Fixed output voltage: 2.7V, 3.0V, 3.3V, 4.5V and 5V. Space saving packages: SOT-23, SOT-89 and TO-92. DESCRIPTION The SS6638G is a high-efficiency step-up DC/DC converter for applications using 1 to 4 NiMH battery cells. Only three external components are required to deliver a fixed output voltage of 2.7V, 3.0V, 3.3V, 4.5V or 5V. The SS6638G starts up from less than 0.9V input with 1mA load. A Pulse Frequency Modulation scheme brings optimized performance for applications with light output loading and low input voltages. The output ripple and noise are lower compared with circuits operating in PSM mode. The PFM control circuit operating at a maximum 100kHz switching rate results in smaller passive components. The space saving SOT-23, SOT-89 and TO-92 packages make the SS6638G an ideal choice of DC/DC converter for space-conscious applications, like pagers, electronic cameras, and wireless microphones. Pb-free, RoHS compliant. APPLICATIONS Pagers. Cameras. Wireless Microphones. Pocket Organizers. Battery Backup Supplies. Portable Instruments. TYPICAL APPLICATION CIRCUIT VIN L1 100µH D1 SS12 SS6638-27G SS6638-30G SS6638-33G SS6638-45G SS6638-50G GND VOUT + C1 SW 22µF VOUT + C2 47µF Simple Step-Up DC/DC Converter 8/21/2005 Rev.2.3 www.SiliconStandard.com 1 of 19 SS6638G ORDERING INFORMATION S S6 638-XX X X X X P acking TR: T ape and reel P ackage type X: SOT-89 Z: TO-92 U: SOT-23 G : P b-f ree , RoHS-compliant O utput voltage 2 7: 2.7V 30: 3.0V 33: 3.3V 45: 4.5V 50: 5.0V E xample: S S6 638-27 G XTR 2 .7V o utput in R oHS-compliant S OT-89 , shipped on tape and reel PIN CONFIGURATION S OT-89 TOP VIEW 1: GND 2: VOUT 3: SW 1 2 3 TO-92 TOP VIEW 1: GND 2: VOUT 3: SW 1 2 3 S OT-23 TOP VIEW 1: GND 2: VOUT 3: SW 1 2 3 SOT-23 MARKING Part No. SS6638-27GU SS6638-30GU SS6638-33GU SS6638-45GU SS6638-50GU SOT-89 MARKING Part No. SS6638-27GX SS6638-30GX SS6638-33GX SS6638-45GX SS6638-50GX DA27P DA30P DA33P DA45P DA50P AN27P AN30P AN33P AN45P AN50P 8/21/2005 Rev.2.3 www.SiliconStandard.com 2 of 19 SS6638G ABSOLUTE MAXIMUM RATINGS Supply Voltage (VOUT pin) SW pin Voltage SW pin Switch Current Operating Temperature Range Maximum Junction Temperature Storage Temperature Range Lead Temperature (Soldering 10 Sec.) .6V 6V 0.6A -40°C to 85°C 125°C -65°C to 150 °C 260°C Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. TEST CIRCUIT IIN VIN D1 SS12 SS6638-27G SS6638-30G SS6638-33G SS6638-45G VOUT SS6638-50G GND VOUT L1 100µH + C1 SW 22µF + C2 47µF Fig. 1 Test Circuit 1 IS SS6638G VOUT GND SW VSW VS SS6638G 100 VOUT GND SW FOSC VS Fig. 2 Test Circuit 2 Fig. 3 Test Circuit 3 8/21/2005 Rev.2.3 www.SiliconStandard.com 3 of 19 SS6638G ELECTRICAL CHARACTERISTICS PARAMETER TEST CONDITIONS SS6638-27G SS6638-30G Output Voltage SS6638-33G SS6638-45G SS6638-50G Input Voltage Start-Up Voltage Min. Hold-on Voltage No-Load Input Current VIN=1.8V VIN=1.8V VIN=2.0V VIN=3.0V VIN=3.0V 1 1 1 1 VIN VSTART VHOLD IIN 15 42 50 60 2 IS1 70 90 µA 0.8 1 VOUT (TA=25°C, IOUT=10mA, unless otherwise specified) (Note1) TEST CKT SYMBOL MIN. 2.633 2.925 3.218 4.387 4.875 TYP. 2.700 3.000 3.300 4.500 5.000 MAX. 2.767 3.075 3.382 4.613 5.125 6 0.9 0.7 UNIT V Normal Operation IOUT=1mA, VIN:0→2V IOUT=1mA, VIN:2→0V IOUT=0mA SS6638-27G SS6638-30G SS6638-33G V V V µA Supply Current SS6638-45G SS6638-50G VS=VOUT x 0.95 Measurement of the IC input current (VOUT pin) SS6638-27G SS6638-30G SS6638-33G SS6638-45G SS6638-50G VS=VOUT + 0.5V Measurement of the IC input current (VOUT pin) 7 7 7 2 IS2 7 7 µA Supply Current SW Leakage Current VSW=6V, VS=VOUT + 0.5V SS6638-27G SS6638-30G SS6638-33G 2 1.3 1.2 1.1 2 RON 1 1 0.5 µA SW Switch-On Resistance SS6638-45G SS6638-50G VS=VOUT x 0.95, VSW=0.4V Ω 8/21/2005 Rev.2.3 www.SiliconStandard.com 4 of 19 SS6638G ELECTRICAL CHARACTERISTICS PARAMETER (Continued) TEST CKT TEST CONDITIONS VS=VOUT x 0.95 SYMBOL MIN. TYP. MAX. UNIT Oscillator Duty Cycle Measurement of the SW pin waveform VS=VOUT x 0.95 3 DUTY 65 75 85 % Max. Oscillator Freq. Efficiency Measurement of the SW pin waveform 3 1 FOSC η 80 105 85 130 kHz % Note 1: Specifications are production tested at TA=25°C. Specifications over the -40°C to 85°C operating temperature range are assured by design, characterization and correlation with Statistical Quality Controls (SQC). TYPICAL PERFORMANCE CHARACTERISTICS (Refer to Typical Application) Capacitor (C2) : 47µF (Tantalum Type) Diode (D1) : 1N5819 Schottky Type 2.8 85 80 2.7 O utput Voltage (V) VIN =1.5V V IN =1.2V 2.5 Efficiency (%) 2.6 VIN =1.8V VIN =2.0V 75 70 VIN=1.8V VIN=2.0V 2.4 65 V IN =0.9V 2.3 60 VIN=1.5V VIN=0.9V 2.2 0 55 VIN=1.2V 40 60 80 100 120 140 160 180 20 40 60 80 100 120 140 160 180 0 20 O utput Current (mA) Fig. 4 SS6638-27G Load Regulation (L=100µH CD54) Output current (mA) Fig. 5 SS6638-27G Efficiency (L=100µH CD54) 2.8 85 80 2.7 75 Output Voltage (V) 2.6 Efficiency (%) VIN=1.2V 2.5 VIN=1.5V VIN=1.8V VIN=2.0V 70 VIN=2.0V 65 60 VIN=1.8V 2.4 VIN=1.2V 55 VIN=1.5V VIN=0.9V VIN=0.9V 2.3 0 20 40 60 80 100 120 140 160 180 200 220 240 50 0 20 40 60 80 100 120 140 160 180 200 220 240 Output Current (mA) Fig. 6 SS6638-27G Load Regulation (L=47µH CD54) Output current (mA) Fig. 7 SS6638-27G Efficiency (L=47µH CD54) 8/21/2005 Rev.2.3 www.SiliconStandard.com 5 of 19 SS6638G TYPICAL PERFORMANCE CHARACTERISTICS (Continued) 1.0 0.9 0.8 1.0 0.9 Start up 0.8 Start up Input Voltage (V) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0 2 4 6 8 10 12 14 16 18 Input Voltage (V) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0 2 4 6 8 10 12 14 16 18 Hold on Hold on Output Current (mA) Fig. 8 SS6638-27G Start-Up & Hold-ON Voltage (L=47µH CD54) Fig. 9 SS6638-27G Start-Up & Hold-ON Voltage (L=100µH CD54) Output Current (mA) 2.80 2.78 2.76 160 Switching Frequency (kHz) 140 Output Voltage (V) 2.74 2.72 2.70 2.68 2.66 2.64 2.62 120 100 80 60 2.60 -40 -20 0 20 40 60 80 100 40 -40 -20 0 20 40 60 80 100 Temperature (°C) Fig. 10 SS6638-27G Output Voltage vs. Temperature Temperature (°C) Fig. 11 SS6638-27G Switching Frequency vs. Temperature 80 1.8 Maximum Duty Cycle (%) 78 SW Turn ON Resistance (Ω) 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 76 74 72 70 -40 0.0 -20 0 20 40 60 80 100 -40 -20 0 20 40 60 80 100 Temperature (°C) Fig. 12 SS6638-27G Maximum Duty Cycle vs. Temperature Temperature (°C) Fig. 13 SS6638-27G SW Turn ON Resistance vs. Temperature 8/21/2005 Rev.2.3 www.SiliconStandard.com 6 of 19 SS6638G TYPICAL PERFORMANCE CHARACTERISTICS (Continued) 45 40 3.1 3.0 2.9 VIN=2.0V VIN=1.8V Output voltage VOUT(V) Supply Current (µA) 35 30 25 20 15 10 2.8 2.7 2.6 2.5 2.4 2.3 2.2 2.1 VIN=1.5V VIN=1.2V VIN=0.9V 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 5 -40 -20 0 20 40 60 80 100 2.0 Temperature (°C) Fig. 14 SS6638-27G Supply Current vs. Temperature Output Current (mA) Fig. 15 SS6638-30G Load Regulation (L=100µH, CD54) 85 80 75 3.1 3.0 2.9 Output Voltage (V) Efficiency (%) 2.8 2.7 2.6 2.5 2.4 VIN=1.2V VIN=1.5V VIN=1.8V VIN=2.0V 70 65 60 55 50 0 20 40 60 80 100 120 140 160 180 VIN=1.8V VIN=1.5V VIN=0.9V VIN=1.2V VIN=2.0 2.3 2.2 0 VIN=0.9V 20 40 60 80 100 120 140 160 180 200 220 Output Current (mA) Output Current (mA) Fig. 16 SS6638-30G Efficiency (L=100µH, CD54) Fig. 17 SS6638-30G Load Regulation (L=47µH CD54) 85 80 75 1.0 0.9 0.8 Start up Input Voltage (V) Efficiency (%) 0.7 0.6 0.5 0.4 0.3 0.2 70 65 Hold on VIN=2.0V 60 55 VIN=1.8V VIN=1.5V VIN=0.9V VIN=1.2V 50 75 100 125 150 175 200 225 0.1 0.0 0 2 4 6 8 10 12 14 16 18 20 50 0 25 Output Current (mA) Fig. 18 SS6638-30G Efficiency (L=47µH CD54) Fig. 19 Output Current (mA) SS6638-30G Start-up & Hold-on Voltage (L=100µH CD54) 8/21/2005 Rev.2.3 www.SiliconStandard.com 7 of 19 SS6638G TYPICAL PERFORMANCE CHARACTERISTICS (Continued) 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0 2 4 6 8 10 12 14 16 18 20 3.10 Start up 3.08 3.06 Output Voltage (V) Input Voltage (V) 3.04 3.02 3.00 2.98 2.96 2.94 2.92 2.90 -40 -20 0 20 No Load Hold on 40 60 80 100 Output Current (mA) Fig. 20 SS6638-30G Start-up & Hold-on Voltage (L=47µH CD54) Fig. 21 Temperature (°C) SS6638-30G Output Voltage vs. Temperature 80 160 Switching Frequency (kHz) 140 120 Maximum Duty Cycle (%) -20 78 76 100 74 80 72 60 40 -40 0 20 40 60 80 100 70 -40 -20 0 20 40 60 80 100 Fig. 22 Temperature (°C) SS6638-30G Switching Frequency vs. Temperature Fig. 23 Temperature (°C) SS6638-30G Maximum Duty Cycle vs. Temperature 1.8 1.6 45 40 35 30 25 20 15 10 SW Turn ON Resistance (Ω) 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -40 -20 0 20 40 60 80 100 Supply Current (µA) 1.4 5 -40 -20 0 20 40 60 80 100 Temperature (°C) Fig. 24 SS6638-30G SW Turn ON Resistance vs. Temperature Fig. 25 Temperature (°C) SS6638-30G Supply Current vs. Temperature 8/21/2005 Rev.2.3 www.SiliconStandard.com 8 of 19 SS6638G TYPICAL PERFORMANCE CHARACTERISTICS (Continued) 3.4 3.3 3.2 90 VIN=2.0V 85 80 Output Voltage (V) 3.1 3.0 2.9 2.8 2.7 2.6 2.5 2.4 2.3 0 25 Efficiency (%) VIN=1.5V VIN=1.8V VIN=2.0V 75 70 65 60 VIN=1.2V VIN=1.8V VIN=1.2V VIN=0.9V 50 75 100 125 150 175 200 55 VIN=1.5V VIN=0.9V 50 0 25 50 75 100 125 150 175 200 Output Current (mA) Fig. 26 SS6638-33G Load Regulation (L=100µH, CD54) Fig. 27 Output Current (mA) SS6638-33G Efficiency (L=100µH, CD54) 3.4 3.3 3.2 90 85 80 Output Voltage (V) Efficiency (%) 3.1 3.0 2.9 2.8 2.7 2.6 2.5 2.4 0 25 VIN=1.5V VIN=1.8V VIN=2.0V 75 70 65 60 55 50 VIN=2.0V VIN=1.2V VIN=0.9V 50 75 100 125 150 175 200 225 VIN=1.5V VIN=0.9V VIN=1.2V VIN=1.8V 45 40 0 25 50 75 100 125 150 175 200 225 250 Fig. 28 Output Current (mA) SS6638-33G Load Regulation (L=47µH, CD54) Output Current (mA) Fig. 29 SS6638-33G Efficiency (L=47µH,CD54) 1.1 1.0 3.50 3.45 Output Voltage Vout (V) 0.9 Start up 3.40 3.35 3.30 3.25 3.20 3.15 3.10 3.05 3.00 -40 -20 0 Input Voltage (V) 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0 2 4 6 8 10 12 14 16 18 20 No Load Hold on Fig. 30 Output Current (mA) SS6638-33G Start-up & Hold-on Voltage (L=100µH CD54) Temperature (°C) 20 40 60 80 100 Fig. 31 SS6638-33G Output Voltage vs. Temperature 8/21/2005 Rev.2.3 www.SiliconStandard.com 9 of 19 SS6638G TYPICAL PERFORMANCE CHARACTERISTICS (Continued) 80 160 Switching Frequency (kHz) 140 120 Maximum Duty Cycle (%) -20 78 76 100 74 80 72 60 40 -40 0 20 40 60 80 100 70 -40 -20 0 20 40 60 80 100 Fig. 32 Temperature (°C) SS6638-33G Switching Frequency vs. Temperature Fig. 33 Temperature (°C) SS6638-33G Maximum Duty Cycle vs. Temperature 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -40 -20 0 20 40 60 80 100 45 40 SW Turn ON Resistance (Ω) Supply Current IDD1 (µA) 35 30 25 20 15 10 -40 -20 0 20 40 60 80 100 Temperature (°C) Fig. 34 SS6638-33G SW Turn ON Resistance vs. Temperature Fig. 35 Temperature (°C) SS6638-33G Supply Current vs. Temperature 4.6 4.4 4.2 90 85 80 Output Voltage (V) 4.0 Efficiency (%) VIN=3.0V 3.8 VIN=1.5V 3.6 3.4 3.2 75 70 VIN=3.0V VIN=2.0V 65 60 55 50 VIN=0.9V VIN=2.0V VIN=1.5V VIN=1.2V VIN=0.9V 3.0 2.8 2.6 2.4 2.2 0 50 VIN=1.2V 100 150 200 250 300 350 400 0 50 100 150 200 250 300 350 400 Fig. 36 Output Current (mA) SS6638-45G Load Regulation (L=100µH) Fig. 37 Output Current (mA) SS6638-45G Efficiency (L=100µH) 8/21/2005 Rev.2.3 www.SiliconStandard.com 10 of 19 SS6638G TYPICAL PERFORMANCE CHARACTERISTICS (Continued) 4.6 4.4 4.2 1.6 1.4 1.2 Output Voltage (V) Input Voltage (V) 4.0 VIN=3.0V 3.8 Start up 1.0 0.8 0.6 0.4 0.2 0.0 VIN=1.5V 3.6 3.4 3.2 VIN=2.0V Hold on VIN=0.9V 3.0 2.8 2.6 2.4 2.2 0 50 VIN=1.2V 100 150 200 250 300 350 400 0 5 10 15 20 Fig. 38 Output Current (mA) SS6638-45G Load Regulation (L=100µH) Fig. 39 Output Current (mA) SS6638-45G Start-up & Hold-On Voltage (L=100µH) 5.0 4.9 4.8 4.7 4.6 90 80 70 60 50 40 30 20 10 -40 -20 0 20 40 60 80 100 No Load 4.5 4.4 4.3 4.2 4.1 4.0 -40 -20 0 20 40 60 80 100 Fig. 40 Temperature (°C) SS6638-45G Output Voltage vs. Temperature Supply Current (µA) Output Voltage (V) Fig. 41 Temperature (°C) SS6638-45G Supply Current vs. Temperature 80 160 Switching Frequency (kHz) 140 120 Maximum Duty Cycle (%) -20 78 76 100 74 80 72 60 40 -40 0 20 40 60 80 100 70 -40 -20 0 20 40 60 80 100 Fig. 42 Temperature (°C) SS6638-45G Switching Frequency vs. Temperature Fig. 43 Temperature (°C) SS6638-45G Maximum Duty Cycle vs. Temperature 8/21/2005 Rev.2.3 www.SiliconStandard.com 11 of 19 SS6638G TYPICAL PERFORMANCE CHARACTERISTICS (Continued) 1.8 1.6 5.5 5.0 SW Turn ON Resistance (Ω) Output Voltage (V) 1.4 1.2 1.0 0.8 0.6 0.4 4.5 VIN=2.0V 4.0 3.5 3.0 2.5 2.0 VIN=3.0V VIN=1.5V VIN=1.2V VIN=0.9V 0.2 0.0 1.5 -40 -20 0 20 40 60 80 100 0 50 100 150 200 250 300 350 400 Temperature (°C) Fig. 44 SS6638-45G SW Turn ON Resistance vs. Temperature Fig. 45 Output Current (mA) SS6638-50G Load Regulation ( L=100µH CD54) 100 90 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 Output Voltage (V) 80 VIN=3.0V VIN=2.0V Efficiency (%) 70 60 VIN=2.0V VIN=3.0V VIN=0.9V 50 40 30 20 VIN=1.5V VIN=1.2V VIN=1.5V VIN=1.2V VIN=0.9V 0 50 100 150 200 250 300 350 400 1.5 0 50 100 150 200 250 300 350 400 Fig. 46 Output Current (mA) SS6638-50G Efficiency (L=100µH CD54) Output Current (mA) Fig. 47 SS6638-50G Load Regulation (L=47µH CD54) 90 1.8 85 1.6 80 1.4 Efficiency (%) 75 70 65 60 55 Input Voltage (V) 1.2 1.0 VIN=3.0V Start up 0.8 0.6 VIN=2.0V VIN=0.9V VIN=1.5V VIN=1.2V Hold on 0.4 0.2 0.0 50 45 0 50 100 150 200 250 300 350 400 0 2 4 6 8 10 12 14 16 18 20 Output Current (mA) Fig. 48 SS6638-50G Efficiency (L=47µH CD54) Output Current (mA) Fig. 49 SS6638-50G Start-up & Hold-on Voltage (L=100µH CD50) 8/21/2005 Rev.2.3 www.SiliconStandard.com 12 of 19 SS6638G TYPICAL PERFORMANCE CHARACTERISTICS (Continued) 5.3 160 5.2 Output Voltage VOUT (V) 5.1 5.0 4.9 4.8 4.7 4.6 4.5 4.4 -40 Switching Frequency (kHz) 60 80 100 140 No Load 120 100 80 60 -20 0 20 40 Temperature (°C) Fig. 50 SS6638-50G Output Voltage vs. Temperature 40 -40 -20 0 20 40 60 80 100 Fig. 51 Temperature (°C) SS6638-50G Switching Frequency vs. Temperature 80 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 Maximum Duty Cycle (%) 78 76 74 72 70 -40 SW Turn ON Resistance (Ω) 0.0 -20 0 20 40 60 80 100 -40 -20 0 20 40 60 80 100 Fig. 52 Temperature (°C) SS6638-50G Maximum Duty Cycle vs. Temperature Temperature (°C) Fig. 53 SS6638-50G SW Turn ON Resistance vs. Temperature 100 90 80 VOUT 50mV/div Supply Current IDD1 (µA) 70 60 50 100mA 40 Load Step 30 20 10 -40 50mA/div -20 0 20 40 60 80 100 Fig. 54 Temperature (°C) SS6638-50G Supply Current vs. Temperature Fig. 55 Load Transient Response (L1=100µH, C2=47µF, VIN=2V) 8/21/2005 Rev.2.3 www.SiliconStandard.com 13 of 19 SS6638G TYPICAL PERFORMANCE CHARACTERISTICS (Continued) VOUT 20mv/div VIN 0.5V/div Fig. 56 Line Transient Response (L1=100µH, C2=47µF) BLOCK DIAGRAM SW V OUT 1M 1 .25V REF. + E nable G ND O SC, 100KHz PIN DESCRIPTIONS PIN 1 : GND - Ground. Must be low impedance; solder directly to ground plane. PIN 2 : VOUT - IC supply pin. Connect VOUT to the converter output. PIN 3 : SW - Internal drain of N-MOSFET switch. 8/21/2005 Rev.2.3 www.SiliconStandard.com 14 of 19 SS6638G APPLICATION INFORMATION GENERAL DESCRIPTION The SS6638G PFM (pulse frequency modulation) converter IC combines a switch mode converter, N-channel power MOSFET, precision voltage reference, and voltage detector in a single monolithic device. I t o ffer s b oth extreme low quiescent current, high efficiency, and very low gate threshold voltage to ensure start-up with low battery voltage (0.8V typ.). Designed to maximize battery life in portable products, i t m inimize s switching losses by only switching as needed to service the load. PFM converters transfer a discrete amount of energy per cycle and regulate the output voltage by modulating t he s witching frequency with a constant p ulse width . Switching frequency depends on load, input voltage, and inductor value, and it can range up to 100kHz. The SW on-resistance is typically 1 to 1.5Ω to minimize switching losses. When the output voltage drops, the error comparator enables the 100KHz oscillator that turns the MOSFET on for about 7.5µs and off for 2.5µs. Turning on the MOSFET allows inductor current to ramp up, storing energy in a magnetic field. When The MOSFET turns off, inductor current is forced through the diode to the output capacitor and load. As the stored energy is depleted, the current ramps down until the diode turns off. At this point, the inductor may ring due to residual energy and stray capacitance. The output capacitor stores charge when the current flowing through the diode is high, and releases it when current is low, thereby maintaining a steady voltage across the load. As the load increases, the output capacitor discharges faster and the error comparator initiates cycles sooner, increasing the switching frequency. The maximum duty cycle ensures adequate time for energy transfer to the output during the second half o f e ach cycle. Depending on t he c ircuit, PFM converters operate in either discontinuous mode o r c ontinuous conduction mode. Continuous conduction mode means that the inductor current does not ramp to zero during each cycle. VIN IIN SW ID IOUT VOUT + EXT Isw Ico SS6638G VEXT IIN IPK ISW Charge Co. ID TDIS Discharge Co. IOUT VSW t Discontinuous Conduction Mode 8/21/2005 Rev.2.3 www.SiliconStandard.com 15 of 19 SS6638G VEXT fsw = IIN IPK IV × TON (VOUT + VD − VSW ) VIN − VSW x )] [1 + ( 2 VOUT + VD − VSW 1  VOUT + VD − VIN    TON  VOUT + VD − VSW  1 (VOUT + VD − VIN) ≅ ISW w here Vsw = switch drop and i s p roportion al to output current. ID IOUT INDUCTOR SELECTION To operate as an efficient energy transfer element, the inductor must fulfill three requirements. First, the inductance must be low enough for the inductor to store adequate energy under the worst-case condition of minimum input voltage and switch ON time. Second, the i nductance must also be high enough so t he maximum current rating of the SS6638 and inductor are not exceeded at the other worst-case condition of maximum input voltage and ON time. Lastly, the inductor must have sufficiently low DC resistance so excessive power is not lost as heat in the windings. Unfortunately this is inversely related to physical size. Minimum and maximum input voltage, output voltage and output current must be established before an inductor can be selected. In discontinuous mode operation, at the end of the switch ON time, peak current and energy in the inductor build according to Ron + Rs  Vin    Ton)  IPK =   1 − exp( − L  Ron + Rs    x  VIN   ≅  (TON) 1 −  2 L  ≅ VIN TON L VSW t Continuous Conduction Mode At the boundary between continuous and discontinuous mode, output current (IOB) is determined by VIN   1 VIN TON(1 − x ) IOB =    VOUT + VD  2 L where VD is the diode drop, x = (RON+Rs)Ton/L. RON= Switch turn on resistance, Rs= Inductor DC resistance TON = Switch ON time In the discontinuous frequency (Fsw) is Fsw = mode, the switching 2(L)(VOUT + VD − VIN)(IOUT) (1 + x ) VIN 2 × TON 2 In the continuous mode, the switching frequency is (Simple losses equation), where x=(RON+RS)TON/L 8/21/2005 Rev.2.3 www.SiliconStandard.com 16 of 19 SS6638G EL = 1 L × IPK 2 2  VOUT + VD − VSW x  IPK =  −  IOUT + VIN − VSW 2  x   VIN − VSW    TON 1 −  2L 2    Power required from the inductor per cycle must be equal or greater than PL/FSW = (VOUT + VD − VIN)(IOUT)( 1 FSW ) Valley current (Iv) is  VIN − VSW   VOUT + VD − VSW x  Iv =  −  IOUT −  × VIN − VSW 2 2L    x  TON 1 −  2  in order for the converter to regulate the output. When loading is over IOB, PFM converter operates in continuous mode. Inductor peak current can be derived from Table 1 Indicates resistance and height for each coil. Inductance Power Inductor Type ( µH ) 22 Coilcraft SMT Type (www.coilcraft.com) DS1608 47 100 DO3316 Sumida SMT Type CD54 Hold Hold SMT Type PM54 SMT Type PM75 22 47 47 100 47 100 33 Resistance (Ω) 0.10 0.18 0.38 0.08 0.14 0.25 0.50 0.25 0.50 0.11 Rated Current (A) 0.7 0.5 0.3 2.7 1.8 0.7 0.5 0.7 0.5 1.2 Height (mm) 2.9 5.2 4.5 4.5 5.0 CAPACITOR SELECTION A poor choice for an output capacitor can result in poor efficiency and high output ripple. Ordinary aluminum electrolytics, while inexpensive, may have unacceptably poor ESR and ESL. There are low ESR aluminum capacitors for switch mode DC-DC converters which work much better than general proposetypes. Tantalum capacitors p rovide still better performance b ut are m ore expensive. OS-CON capacitors have extremely low ESR in a small size. If capacitance is reduced, output ripple will increase. Most of the input supply is provided by the input bypass capacitor; the capacitor voltage rating s hould be at least 1.25 times greater than t he maximum input voltage. DIODE SELECTION Speed, forward drop, and leakage current are the three main considerations in selecting a rectifier diode. Best performance is obtained with a S chottky rectifier diode, such as t he 1N5818, or the SS13 and B0530W in surface mount packages. For lower output power a 1N4148 can be used although efficiency and start-up voltage will suffer substantially. 8/21/2005 Rev.2.3 www.SiliconStandard.com 17 of 19 SS6638G COMPONENT POWER DISSIPATION Operating in discontinuous mode, power loss in the winding resistance of inductor can be approximated to PD L = 2  TON   VOUT + VD   (POUT )   (Rs )  3 L   VOUT  VD = Diode drop. The power dissipated due to the switch loss is PDsw = 2  TON   VOUT + VD − VIN   (POUT )   (RON)  3 L  VOUT   The power dissipated in the rectifier diode is  VD  PDD =   (POUT)  VOUT  where POUT=VOUT ×IOUT ; Rs=Inductor DC R; PHYSICAL DIMENSIONS (unit: mm) SOT-23-3 (GU) D SYMBOL A 0.25 MIN 0.95 0.05 0.90 0.30 0.08 2.80 2.60 1.50 0.95 BSC 1.90 BSC 0.30 0.60 REF 0˚ MAX 1.45 0.15 1.30 0.50 0.22 3.00 3.00 1.70 A1 A2 b c D E E1 E1 e e1 E c L L1 θ A2 A A1 b e e1 L L1 θ 0.60 8˚ 8/21/2005 Rev.2.3 www.SiliconStandard.com 18 of 19 SS6638G PHYSICAL DIMENSIONS (unit: mm) (Continued) SOT-89-3 (GX) D D1 C A SYMBOL A B B1 C MIN 1.40 0.44 0.36 0.35 4.40 1.50 2.29 1.50 BSC 3.00 BSC 3.94 0.89 MAX 1.60 0.56 0.48 0.44 4.60 1.83 2.60 H E D D1 E L e e1 B B1 e e1 H L 4.25 1.20 TO-92 (GZ) SYMBOL A A D MIN 4.32 0.36 4.45 3.18 2.42 1.15 3.43 12.70 2.03 MAX 5.33 0.47 5.20 4.19 2.66 1.39 2.66 b D E e b S E e1 j L S L j e1 e Information furnished by Silicon Standard Corporation is believed to be accurate and reliable. However, Silicon Standard Corporation makes no guarantee or warranty, express or implied, as to the reliability, accuracy, timeliness or completeness of such information and assumes no responsibility for its use, or for infringement of any patent or other intellectual property rights of third parties that may result from its use. Silicon Standard reserves the right to make changes as it deems necessary to any products described herein for any reason, including without limitation enhancement in reliability, functionality or design. No license is granted, whether expressly or by implication, in relation to the use of any products described herein or to the use of any information provided herein, under any patent or other intellectual property rights of Silicon Standard Corporation or any third parties. 8/21/2005 Rev.2.3 www.SiliconStandard.com 19 of 19