SS6638-27GUTR

SS6638G SSC | Alldatasheet

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www.SiliconStandard.com 1 of 19 SS6638G 8/21/2005 Rev.2.3 Simple 3-Pin Step-Up DC/DC Converter FEATURES DESCRIPTION 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.

APPLICATIONS

Pagers. Cameras. Wireless Microphones. Pocket Organizers. Battery Backup Supplies. Portable Instruments. 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. TYPICAL APPLICATION CIRCUIT SS12 VOUTSW GND SS6638-27G SS6638-30G SS6638-33G SS6638-45G SS6638-50G 47µF VOUT 100µH VIN + C1 22µF Simple Step-Up DC/DC Converter Pb-free, RoHS compliant.

www.SiliconStandard.com 2 of 19 ORDERING INFORMATION PIN CONFIGURATION Packing TR: Tape and reel Package type X: SOT-89 Z: TO-92 U: SOT-23 G: Pb-free, RoHS-compliant Output voltage 27: 2.7V 30: 3.0V 33: 3.3V 45: 4.5V 50: 5.0V SS6638-XX X X XX Example: SS6638-27 GXTR Æ 2.7V output in RoHS-compliant SOT-89, shipped on tape and reel TO-92 TOP VIEW 1: GND 2: VOUT 3: SW 123 SOT-89 TOP VIEW 1: GND 2: VOUT 3: SW SOT-23 TOP VIEW 1: GND 2: VOUT 3: SW SOT-23 MARKING Part No. SS6638-27GU DA27P SS6638-30GU DA30P SS6638-33GU DA33P SS6638-45GU DA45P SS6638-50GU DA50P SOT-89 MARKING Part No. SS6638-27GX AN27P SS6638-30GX AN30P SS6638-33GX AN33P SS6638-45GX AN45P SS6638-50GX AN50P SS6638G 8/21/2005 Rev.2.3

www.SiliconStandard.com 3 of 19 ABSOLUTE MAXIMUM RATINGS Supply Voltage (VOUT pin) .6V SW pin Voltage 6V SW pin Switch Current 0.6A Operating Temperature Range -40°C to 85°C Maximum Junction Temperature 125°C Storage Temperature Range -65 °C to 150 °C Lead Temperature (Soldering 10 Sec.) 260°C Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. TEST CIRCUIT SS12 VOUTSW GND SS6638-27G SS6638-30G SS6638-33G SS6638-45G SS6638-50G 47µF VOUT 100µH VIN + C1 22µF IIN Fig. 1 Test Circuit 1 VS VSW SS6638G VOUT SW GND IS VS FOSC SS6638G VOUT SW 100 GND Fig. 2 Test Circuit 2 Fig. 3 Test Circuit 3 SS6638G 8/21/2005 Rev.2.3

www.SiliconStandard.com 4 of 19 ELECTRICAL CHARACTERISTICS (T A=25°C, IOU T=10mA, unless otherwise specified) (Note1) PARAMETER TEST CONDITIONS TEST CKT SYMBOL MIN. TYP. MAX. UNIT Output Voltage SS6638-27G V IN=1.8V SS6638-30G V IN=1.8V SS6638-33G V IN=2.0V SS6638-45G V IN=3.0V SS6638-50G V IN=3.0V

1 VOUT

2.633 2.925 3.218 4.387 4.875 2.700 3.000 3.300 4.500 5.000 2.767 3.075 3.382 4.613 5.125 V Input Voltage Normal Operation 1 VIN 6 V Start-Up Voltage IOUT=1mA, VIN:0→2V 1 VSTART 0.8 0.9 V Min. Hold-on Voltage IOUT=1mA, VIN:2→0V 1 VHOLD 0.7 V No-Load Input Current IOUT=0mA 1 IIN 15 µA Supply Current SS6638-27G SS6638-30G SS6638-33G SS6638-45G SS6638-50G VS=VOUT x 0.95 Measurement of the IC input current (VOUT pin)

2 IS1

µA Supply Current SS6638-27G SS6638-30G SS6638-33G SS6638-45G SS6638-50G VS=VOUT + 0.5V Measurement of the IC input current (VOUT pin)

2 IS2

µA SW Leakage Current VSW=6V, VS=VOUT + 0.5V 2 0.5 µA SW Switch-On Resistance SS6638-27G SS6638-30G SS6638-33G SS6638-45G SS6638-50G VS=VOUT x 0.95, VSW=0.4V

2 RON

1.3 1.2 1.1 Ω SS6638G 8/21/2005 Rev.2.3

www.SiliconStandard.com 5 of 19 ELECTRICAL CHARACTERISTICS (Continued) PARAMETER TEST CONDITIONS TEST CKT SYMBOL MIN. TYP. MAX. UNIT Oscillator Duty Cycle VS=VOUT x 0.95 Measurement of the SW pin waveform

3 DUTY 65 75 85 %

Max. Oscillator Freq. VS=VOUT x 0.95 Measurement of the SW pin waveform

3 FOSC 80 105 130 kHz

Efficiency 1 η 85 % Note 1: Specifications are prod uction tested at T A=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 Fig. 4 SS6638-27G Load Regulation (L=100µH CD54) 0 20 40 60 80 100 120 140 160 180 2.2 2.3 2.4 2.5 2.6 2.7 2.8 VIN=2.0VVIN=1.8VVIN=1.5V VIN=1.2V VIN=0.9V Output Voltage (V) Output Current (mA) Fig. 5 SS6638-27G Efficiency (L=100µH CD54) 0 20 40 60 80 100 120 140 160 180 VIN=2.0V VIN=1.8V VIN=1.5V VIN=1.2V VIN=0.9V Efficiency (%) Output current (mA) Fig. 6 SS6638-27G Load Regulation ( L=47µH CD54) 0 20 40 60 80 100 120 140 160 180 200 220 2402.3 2.4 2.5 2.6 2.7 2.8 VIN=2.0V VIN=1.8V VIN=1.5V VIN=1.2V VIN=0.9V Output Voltage (V) Output Current (mA) 240 Fig. 7 SS6638-27G Efficiency (L=47µH CD54) Efficiency (%) Output current (mA) 0 20 40 60 80 100 120 140 160 180 200 220 VIN=2.0V VIN=1.8V VIN=1.5V VIN=1.2V VIN=0.9V SS6638G 8/21/2005 Rev.2.3

www.SiliconStandard.com 6 of 19 TYPICAL PERFORMANCE CHARACTERISTICS (Continued) Fig. 8 SS6638-27G Start-Up & Hold-ON Voltage (L=47 µH CD54) 0 2 4 6 8 10 12 14 16 18 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Start up Hold on Input Voltage (V) Output Current (mA) Fig. 9 SS6638-27G Start-Up & Hold-ON Voltage (L=100µH CD54) 0 2 4 6 8 10 12 14 16 180.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Start up Hold on Input Voltage (V) Output Current (mA) Fig. 10 SS6638-27G Ou tput Voltage vs. Temperature Output Voltage (V) Temperature (°C) -40 -20 0 20 40 60 80 100 2.60 2.62 2.64 2.66 2.68 2.70 2.72 2.74 2.76 2.78 2.80 Fig. 11 SS6638-27G Switching Frequency vs. Temp erature Switching Frequency (kHz) Temperature (°C) -40 -20 0 20 40 60 80 100 100 120 140 160 Fig. 12 SS6638-27G Maximum Duty Cycle vs. TemperatureMaximum Duty Cycle (%) Temperature (°C) -40 -20 0 20 40 60 80 100 Fig. 13 SS6638-27G SW Turn ON Resistance vs. TemperatureSW Turn ON Resistance (Ω) Temperature (°C) -40 -20 0 20 40 60 80 100 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 SS6638G 8/21/2005 Rev.2.3

www.SiliconStandard.com 7 of 19 TYPICAL PERFORMANCE CHARACTERISTICS (Continued) Fig. 14 SS6638-27G Supply Current vs. Temperature Supply Current (µA) Temperature (°C) -40 -20 0 20 40 60 80 100 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 3.1 VIN=2.0V VIN=1.8VVIN=1.5V VIN=1.2V VIN=0.9V Fig. 15 SS6638-30G Load Regulation (L=100 µH, CD54) Output voltage VOUT(V) Output Current (mA) 0 20 40 60 80 100 120 140 160 180 VIN=2.0 VIN=1.8V VIN=1.5V VIN=1.2V VIN=0.9V Fig. 16 SS6638-30G Efficiency (L=100 µH, CD54) Efficiency (%) Output Current (mA) Fig. 17 SS6638-30G Load Regulation (L=47 µH CD54) 0 20 40 60 80 100 120 140 160 180 200 220 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 3.1 VIN=2.0VVIN=1.8VVIN=1.5V VIN=1.2V VIN=0.9V Output Voltage (V) Output Current (mA) 225 Fig. 18 SS6638-30G Efficiency (L=47µH CD54) 0 25 50 75 100 125 150 175 200 50 VIN=2.0V VIN=1.8V VIN=1.5V VIN=1.2V VIN=0.9V Efficiency (%) Output Current (mA) 0 2 4 6 8 10 12 14 16 18 20 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Fig. 19 SS6638-30G Start-up & Hold-on Voltage (L=100 µH CD54) Start up Hold on Input Voltage (V) Output Current (mA) SS6638G 8/21/2005 Rev.2.3

www.SiliconStandard.com 8 of 19 TYPICAL PERFORMANCE CHARACTERISTICS (Continued) 0 2 4 6 8 10 12 14 16 18 20 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Fig. 20 SS6638-30G Start-up & Hold-on Voltage (L=47 µH CD54) Start up Hold on Input Voltage (V) Output Current (mA) Fig. 21 SS6638-30G Output Voltage vs. Temperature Output Voltage (V) Temperature (°C) -40 -20 0 20 40 60 80 100 2.90 2.92 2.94 2.96 2.98 3.00 3.02 3.04 3.06 3.08 3.10 No Load Fig. 22 SS663 8-30G Switching Frequency vs. Temperature Switching Frequency (kHz) Temperature (°C) -40 -20 0 20 40 60 80 100 100 120 140 160 Fig. 23 SS6638-30G Maximum Duty Cycle vs. TemperatureMaximum Duty Cycle (%) Temperature (°C) -40 -20 0 20 40 60 80 100 Fig. 24 SS6638-30G SW Turn ON Resistance vs. TemperatureSW Turn ON Resistance (Ω) Temperature (°C) -40 -20 0 20 40 60 80 100 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 Fig. 25 SS6638-30G Supply Current vs. Temperature Supply Current (µA) Temperature (°C) -40 -20 0 20 40 60 80 100 SS6638G 8/21/2005 Rev.2.3

www.SiliconStandard.com 9 of 19 TYPICAL PERFORMANCE CHARACTERISTICS (Continued) 0 25 50 75 100 125 150 175 200 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 VIN=2.0V VIN=1.8V VIN=1.5V VIN=1.2V VIN=0.9V Fig. 26 SS6638-33G Load Regulation (L=100 µH, CD54) Output Voltage (V) Output Current (mA) 0 25 50 75 100 125 150 175 200 VIN=2.0V VIN=1.8V VIN=1.5V VIN=1.2V VIN=0.9V Fig. 27 SS6638-33G Efficiency (L=100 µH, CD54) Efficiency (%) Output Current (mA) 0 25 50 75 100 125 150 175 200 225 2.4 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 Fig. 28 SS6638-33 G Load Regulation (L=47µH, CD54) VIN=2.0VVIN=1.8V VIN=1.5V VIN=1.2V VIN=0.9V Output Voltage (V) Output Current (mA) 0 25 50 75 100 125 150 175 200 225 250 VIN=2.0V VIN=1.8V VIN=1.5V VIN=1.2V VIN=0.9V Fig. 29 SS6638-33G Efficiency (L=47µH,CD54) Efficiency (%) Output Current (mA) 0 2 4 6 8 10 12 14 16 18 20 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 Fig. 30 SS6638-33G Start-up & Hold-on Voltage (L=100 µH CD54) Start up Hold on Input Voltage (V) Output Current (mA) Fig. 31 SS6638-33G Output Voltage vs. Temperature Output Voltage Vout (V) Temperature (°C) -40 -20 0 20 40 60 80 100 3.00 3.05 3.10 3.15 3.20 3.25 3.30 3.35 3.40 3.45 3.50 No Load SS6638G 8/21/2005 Rev.2.3

www.SiliconStandard.com 10 of 19 TYPICAL PERFORMANCE CHARACTERISTICS (Continued) Fig. 32 SS663 8-33G Switching Frequency vs. Temperature Switching Frequency (kHz) Temperature (°C) -40 -20 0 20 40 60 80 100 100 120 140 160 Fig. 33 SS6638-33G Maximum Duty Cycle vs. TemperatureMaximum Duty Cycle (%) Temperature (°C) -40 -20 0 20 40 60 80 100 Fig. 34 SS6638-33G SW Turn ON Resistance vs. TemperatureSW Turn ON Resistance (Ω) Temperature (°C) -40 -20 0 20 40 60 80 100 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 Fig. 35 SS6638-33G Supply Current vs. Temperature Supply Current IDD1 (µA) Temperature (°C) -40 -20 0 20 40 60 80 100 Fig. 36 SS6638-45G Load Regulation (L=100 µH) Output Voltage (V) Output Current (mA) 0 50 100 150 200 250 300 350 400 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 VIN=3.0V VIN=1.5V VIN=2.0V VIN=1.2V VIN=0.9V Fig. 37 SS6638-45G Efficien cy (L=100µH) Efficiency (%) Output Current (mA) 0 50 100 150 200 250 300 350 400 VIN=3.0V VIN=1.5V VIN=2.0V VIN=1.2V VIN=0.9V SS6638G 8/21/2005 Rev.2.3

www.SiliconStandard.com 11 of 19 TYPICAL PERFORMANCE CHARACTERISTICS (Continued) Fig. 38 SS6638-45G Load Regulation (L=100 µH) Out put Voltage (V) Output Current (mA) 0 50 100 150 200 250 300 350 400 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 VIN=3.0V VIN=1.5V VIN=2.0V VIN=1.2V VIN=0.9V Fig. 39 SS6638-45G Start-up & Hold-On Voltage (L=100 µH) Input Voltage (V) Output Current (mA) 0 5 10 15 20 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Hold on Start up Fig. 40 SS6638-45G Output Voltage vs. Temperature Output Voltage (V) Temperature (°C) -40 -20 0 20 40 60 80 100 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5.0 No Load Fig. 41 SS6638-45G Supply Current vs. Temperature Supply Current (µA) Temperature (°C) -40 -20 0 20 40 60 80 100 Fig. 42 SS663 8-45G Switching Frequency vs. Temperature Switching Frequency (kHz) Temperature (°C) -40 -20 0 20 40 60 80 100 100 120 140 160 Fig. 43 SS6638-45G Maximum Duty Cycle vs. TemperatureMaximum Duty Cycle (%) Temperature (°C) -40 -20 0 20 40 60 80 100 SS6638G 8/21/2005 Rev.2.3

www.SiliconStandard.com 12 of 19 TYPICAL PERFORMANCE CHARACTERISTICS (Continued) Fig. 44 SS6638-45G SW Turn ON Resistance vs. TemperatureSW Turn ON Resistance (Ω) Temperature (°C) -40 -20 0 20 40 60 80 100 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 0 50 100 150 200 250 300 350 400 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VIN=1.2V VIN=3.0V VIN=2.0V VIN=1.5V VIN=0.9V Fig. 45 SS6638-50 G Load Regulation ( L=100µH CD54) Output Voltage (V) Output Current (mA) 0 50 100 150 200 250 300 350 400 100 VIN=1.2V Fig. 46 SS6638-50G Efficiency (L=100 µH CD54) VIN=3.0V VIN=2.0V VIN=1.5V VIN=0.9V Efficiency (%) Output Current (mA) 0 50 100 150 200 250 300 350 400 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 Fig. 47 SS6638-50G Load Regulation (L=47 µH CD54) VIN=1.2V VIN=3.0V VIN=2.0V VIN=1.5V VIN=0.9V Output Voltage (V) Output Current (mA) 0 50 100 150 200 250 300 350 400 Fig. 48 SS6638-50G Efficiency (L=4 7µH CD54) Efficiency (%) Output Current (mA) VIN=1.2V VIN=3.0V VIN=2.0V VIN=1.5V VIN=0.9V 0 2 4 6 8 10 12 14 16 18 20 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 Fig. 49 SS6638-50G Start-up & Hold-on Voltage (L=100 µH CD50) Input Voltage (V) Output Current (mA) Start up Hold on SS6638G 8/21/2005 Rev.2.3

www.SiliconStandard.com 13 of 19 TYPICAL PERFORMANCE CHARACTERISTICS (Continued) Fig. 50 SS6638-50G Output Voltage vs. Temperature Output Voltage VOUT (V) Temperature (°C) -40 -20 0 20 40 60 80 100 4.4 4.5 4.6 4.7 4.8 4.9 5.0 5.1 5.2 5.3 No Load Fig. 51 SS6638-50G Swit ching Frequency vs. Temperature Switching Frequency (kHz) Temperature (°C) -40 -20 0 20 40 60 80 100 100 120 140 160 Fig. 52 SS6638-50G Maximum Duty Cycle vs. TemperatureMaximum Duty Cycle (%) Temperature (°C) -40 -20 0 20 40 60 80 100 Fig. 53 SS6638-50G SW Turn ON Resistance vs. TemperatureSW Turn ON Resistance (Ω) Temperature (°C) -40 -20 0 20 40 60 80 100 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 -40 -20 0 20 40 60 80 100 100 Fig. 54 SS6638-50G Supply Current vs. Temperature Supply Current IDD1 (µA) Temperature (°C) VOUT 50mV/div 100mA Load Step 50mA/div Fig. 55 Load Transient Response (L1=100µH, C2=47µF, VIN=2V) SS6638G 8/21/2005 Rev.2.3

www.SiliconStandard.com 14 of 19 TYPICAL PERFORMANCE CHARACTERISTICS (Continued) VOUT 20mv/div VIN 0.5V/div Fig. 56 Line Transient Response (L 1=100µH, C2=47µF) BLOCK DIAGRAM GND VOUT SW 1.25V REF. Enable OSC, 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. SS6638G 8/21/2005 Rev.2.3

www.SiliconStandard.com 15 of 19

APPLICATION INFORMATION

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. It offers both 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, it minimizes 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 the switching frequency with a constant pulse 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 drop s, 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 of each cycle. Depending on the circuit, PFM converters operate in either discontinuous mode or continuous conduction mode. Continuous conduction mode means that the inductor current does not ramp to zero during each cycle. VIN SW VOUT EXT ID IOUT Isw Ico IIN SS6638G IPK IIN VEXT ISW IOUT TDIS Charge Co. VSW Discharge Co. ID t Discontinuous Conduction Mode SS6638G 8/21/2005 Rev.2.3

www.SiliconStandard.com 16 of 19 IPK IIN VEXT ISW IOUT VSW ID t IV ( ) )]VVV VV(2 x[1 )VV(V VVV T 1fsw SWDOUT SWIN SWDOUT INDOUT ON ×−+ −+= −+≅ SWDOUT INDOUT ON VVV VVV T where Vsw = switch drop and is proportional to output current. INDUCTOR SELECTION To op erate as a n eff icient e nergy transfer element, the inductor must ful fill three requirements. First, the inducta nce mu st be lo w enough for the inductor to store adequate energy under the wo rst-case condition of minimum input voltage an d switch O N time. Second, the inductance must also be high enough so the maximum current rating of the SS6638 and inductor are not exceeded at the other worst-case condition of maximum input voltage and O N time. Lastly, the indu ctor 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. Continuous Conduction Mode At the bou ndary between continuous and discontinuous mode, output current (IOB) i s determined by () x1TL V VV VI ONIN DOUT INOB − where VD is the diode drop, Minimum an d maximum input voltage, output voltage and output cu rrent must be establish ed before an inductor can be selected. x = (RON+Rs)Ton/L. RON= Switch turn on resistance, Rs= Inductor DC resistance In discontin uous mode o peration, at the en d of the switch ON time, pea k current and energy in the inductor build according to TON = Switch ON time In the discontin uous mode, the switchi ng frequency (Fsw) is   +−− += Ton)L RsRonexp(1 RsRon VinIPK )x(12T2V ))(IVV2(L)(VFsw ONIN OUTINDOUT −+= ()   − ≅ 2 x1 T L V ON IN In the contin uous mode, the switchi ng frequency is ON IN T L V≅ (Simple losses equation), where x=(RON+RS)TON/L SS6638G 8/21/2005 Rev.2.3

www.SiliconStandard.com 17 of 19 2IL2 1EL PK×=  −  −  −− −+= x1T 2L VV I 2 x VV VVVI ON SWIN OUT SWIN SWDOUT PK Power required from the inductor per cycle mu st be equal or greater than 1)()(IVIV(V/FP SW OUTNDOUTSWL −+= Valley current (Iv) is  −  −−  −− −+= x1T VVI 2 x VV VVVIv ON SWIN OUT SWIN SWDOUT in order for the converter to regulate the output. When loadi ng is over I OB, PFM converte r operates in continu ous mode. Inducto r pea k current can be derived from Table 1 Indicates resistance and height for each coil. Power Inductor Type Inductance ( µH ) Resistance ( Ω ) Rated Current (A) Height (mm) 22 0.10 0.7 47 0.18 0.5 DS1608 100 0.38 0.3 2.9 22 0.08 2.7 Coilcraft SMT Type (www.coilcraft.com) DO3316 47 0.14 1.8 5.2 47 0.25 0.7 Sumida SMT Type CD54 100 0.50 0.5 4.5 47 0.25 0.7 Hold SMT Type PM54 100 0.50 0.5 4.5 Hold SMT Type PM75 33 0.11 1.2 5.0 CAPACITOR SELECTION A poor choice for an output capacitor can result in poor efficie ncy and high output ri pple. Ordinary aluminum el ectrolytics, while inexpensive, may have unacceptably poor ESR and ESL. There are low ESR alu minum ca pacitors for swi tch mode DC-DC converters which work much better tha n general p roposetypes. Tantalum capacitors provide still better performance but are more expensive. O S-CON capacitors have extremely low ESR in a small size. If capa citance is reduced, output ripple will increase. Most of the input su pply is provided by the input bypass cap acitor; the capacitor voltage rating should be at least 1.25 times greater than the maximum input voltage. DIODE SELECTION Speed, forward drop, and leakage current are the three main considerations in selecting a rectifier diode. Be st performance is obtained wit h a Schottky rectifier diode, such as the 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. SS6638G 8/21/2005 Rev.2.3

www.SiliconStandard.com 18 of 19 COMPONENT POWER DISSIPATION Operating in discontinuous mode, power loss in the winding resistance of inductor can be approximated to () ()OUT OUT DOUTON L P V V V Rs L T 3 2PD   + where POUT=VOUT ×IOUT ; Rs=Inductor DC R; VD = Diode drop. The power dissipated due to the switch loss is () ()OUT OUT IN DOUT ON ON P V V V V R L T 3 2PDsw   − + The power dissipated in the rectifier diode is ) (P V VPD OUT OUT D D  PHYSICAL DIMENSIONS (unit: mm) SOT-23-3 (GU) SYMBOL MIN MAX A 0.95 1.45 A1 0.05 0.15 A2 0.90 1.30 b 0.30 0.50 c 0.08 0.22 D 2.80 3.00 E 2.60 3.00 E1 1.50 1.70 e 0.95 BSC e1 1.90 BSC L 0.30 0.60 L1 0.60 REF E D e A A2 b 0.25 L θ c θ 0˚ 8˚ SS6638G 8/21/2005 Rev.2.3

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. www.SiliconStandard.com 19 of 19 PHYSICAL DIMENSIONS (unit: mm) (Continued) SOT-89-3 (GX) SYMBOL MIN MAX A 1.40 1.60 B 0.44 0.56 B1 0.36 0.48 C 0.35 0.44 D 4.40 4.60 D1 1.50 1.83 E 2.29 2.60 e 1.50 BSC e1 3.00 BSC H 3.94 4.25 e H D A C L E B L 0.89 1.20 TO-92 (GZ) SYMBOL MIN MAX A 4.32 5.33 b 0.36 0.47 D 4.45 5.20 E 3.18 4.19 e 2.42 2.66 e1 1.15 1.39 j 3.43 - L 12.70 - S 2.03 2.66 A e L D S E j b SS6638G 8/21/2005 Rev.2.3