AIC1638 3-PIN ONE-CELL STEP-UP DC/DC CONVERTER SPEC NO: DS-1638-00 03/01/00 FEATURES ! ! ! ! ! ! ! DESCRIPTION Guaranteed Start-Up from below 0.9 V. High Efficiency. Low Quiescent Current. Few Number of External Components needed. Low Ripple and Low Noise. Fixed Output Voltage: 2.7V, 3.0V, 3.3V, and 5V. Space Saving SOT-89 and TO-92 Packages. The AIC1638 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, or 5V. The AIC1638 starts up from below 0.9V input with 1mA load. 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 the circuits operating in PSM mode. APPLICATIONS ! ! ! ! ! ! Pagers. Cameras. Wireless Microphones. Pocket Organizers. Battery Backup Suppliers. Portable Instruments. The PFM control circuit operating in 100KHz (max.) switching rate results in smaller passive components. The space saving SOT-89 and TO-92 packages make the AIC1638 an ideal choice of DC/DC converter for space conscious applications, like pagers, electronic cameras, and wireless microphones TYPICAL APPLICATION CIRCUIT VIN + C2 47µF L1 88µH D1 VOUT SW AIC1638-27 AIC1638-30 AIC1638-33 AIC1638-50 VOUT + GND C1 22µF One Cell Step-Up DC/DC Converter ANALOG INTEGRATIONS CORPORATION 4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C. www.analog.com.tw TEL: (8863)577-2500 FAX:(8863)577-2510 1 AIC1638 3-PIN ONE-CELL STEP-UP DC/DC CONVERTER SPEC NO: DS-1638-00 03/01/00 ORDERING INFORMATION AIC1638- XXX ORDER NUMBER AIC1638-27CX AIC1638-30CX AIC1638-33CX AIC1638-50CX (SOT-89) PACKAGE TYPE X: SOT-89 Z: TO-92 PIN CONFIGURATION TOP VIEW 1: GND 2: VOUT 3: SW TEMPERATURE RANGE C: -20°C+80°C 1 OUTPUT VOLTAGE 27: 2.7V 30: 3.0V 33: 3.3V 50: 5.0V AIC1638-27CZ AIC1638-30CZ AIC1638-33CZ AIC1638-50CZ (TO-92) TOP VIEW 1: GND 2: VOUT 3: SW 2 3 1 2 3 ABSOLUATE MAXIMUM RATINGS Supply Voltage ………………………………………………………………………….12V SW pin Voltage ………………………………………….…………………………………….12V SW pin Switch Current Power Dissipation ……………………………………………………………………0.6A ……………………………………………………..……………….500mW Operating Temperature Range ………………………………..…………….….-20°C to 80 °C Storage Temperature Range ………………………………………………… -65°C to 150 °C Lead Temperature (Sordering 10 Sec.) …………………………………………………260°C TEST CIRCUIT AIC1638 2.5V VOUT 100 FOUT SW GND Oscillator Test Circuit ANALOG INTEGRATIONS CORPORATION www.analog.com.tw 4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C. TEL: (8863)577-2500 FAX:(8863)577-2510 2 AIC1638 3-PIN ONE-CELL STEP-UP DC/DC CONVERTER SPEC NO: DS-1638-00 03/01/00 " ELECTRICAL CHARACTERISTICS PARAMETER Output Voltage (Ta=25°°C, IO=10mA, Unless otherwise specified) SYMBOL MIN. TYP. MAX. UNIT VOUT 2.633 2.700 2.767 V VIN=1.8V 2.925 3.000 3.075 VIN=2.0V 3.218 3.300 3.382 VIN=3.0V 4.875 5.000 5.125 TEST CONDITIONS VIN=1.8V Input Voltage VIN Start-Up Voltage IOUT=1mA, VIN:0→2V VSTART Min. Hold-on Voltage IOUT=1mA, VIN:2→0V VHOLD No-Load Input Current IOUT=0mA Supply Current VIN=VOUT x 0.95 0.8 8 V 0.9 V 0.7 V IIN 15 µA IDD1 42 µA 50 Measurement of the IC input current 60 90 Supply Current VIN=VOUT + 0.5V 7 IDD2 µA Measurement of the IC input current SW Leakage Current VSW =10V, VIN=VOUT + 0.5V SW Switch-On Resistance VIN=VSW x 0.95, VSW =0.4V 0.5 1.3 RON µA Ω 1.2 1.1 1 Oscillator Duty Cycle VIN=VOUT x 0.95 DUTY 65 75 85 % FOSC 80 105 130 KHz Measurement of the IC input current Max. Oscillator Freq. VIN=VOUT x 0.95 Measurement of the IC input current Efficiency η 85 ANALOG INTEGRATIONS CORPORATION www.analog.com.tw 4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C. TEL: (8863)577-2500 FAX:(8863)577-2510 % 3 AIC1638 3-PIN ONE-CELL STEP-UP DC/DC CONVERTER SPEC NO: DS-1638-00 03/01/00 " TYPICAL PERFORMANCE CHARACTERISTICS Capacitor (C1) : 47 µ F (Tantalum Type) Diode (D1) : 1N5819 Schottky Type AIC1638-27 Load Regulation (L=100µH CD54) 80 2.7 2.6 VIN=1.8V VIN=1.5V 75 VIN=2.0V Efficiency (%) Output voltage (V) AIC1638-27 Efficiency (L=100µH CD54) 85 2.8 VIN=1.2V 2.5 2.4 VIN=1.8V 70 VIN=2.0V 65 VIN=1.5V VIN=0.9V 60 2.3 VIN=1.2V VIN=0.9V 55 2.2 0 20 40 60 80 100 120 140 160 0 180 20 40 60 80 100 120 140 160 180 Output current (mA) Output Current (mA) AIC1638-27 Efficiency AIC1638-27 Load Regulation (L=47µH CD54) (L=47µH CD54) 85 2.8 80 2.7 2.6 VIN=1.5V VIN=1.2V Efficiency (%) Output voltage (V) 75 VIN=2.0V VIN=1.8V 2.5 70 VIN=2.0V VIN=1.8V 65 60 VIN=1.2V 2.4 VIN=1.5V VIN=0.9V 55 VIN=0.9V 2.3 0 20 40 60 80 100 120 140 160 180 200 220 50 240 0 20 40 60 80 Output Current (mA) 1.0 0.9 0.9 Input Voltage (V) Input Voltage (V) 0.7 0.6 0.5 Hold on 0.3 6 8 10 220 240 12 Output Current (mA) 14 16 18 0.3 0.0 Hold on 0.4 0.1 4 200 0.5 0.2 2 180 0.6 0.1 0 160 0.7 0.2 0.0 140 Start up 0.8 Start up 0.4 120 AIC1638-27 Start-Up & Hold-ON Voltage (L=100µH) AIC1638-27 Start-Up & Hold-ON Voltage (L=47µH) 1.0 0.8 100 Output current (mA) 0 2 4 6 8 10 12 14 16 18 Output Current (mA) ANALOG INTEGRATIONS CORPORATION www.analog.com.tw 4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C. TEL: (8863)577-2500 FAX:(8863)577-2510 4 AIC1638 3-PIN ONE-CELL STEP-UP DC/DC CONVERTER SPEC NO: DS-1638-00 03/01/00 " TYPICAL PERFORMANCE CHARACTERISTICS (CONTINUED) AIC1638-27 Output Voltage vs Temperature AIC1638-27 Switching Frequency vs Temperature 2.78 160 140 Switching Frequency (kHz) Output Voltage Vout (V) 2.76 No Load 2.74 2.72 2.70 2.68 2.66 120 100 80 60 40 2.64 2.62 -40 -20 0 20 40 60 80 20 -40 100 -20 0 20 Temperature (°C) AIC1638-27 Maximum Duty Cycle vs Temperature 100 1.6 SW Turn On Resistance (Ω) Maximum Duty Cycle (%) 80 AIC1638-27 SW On Resistance vs Temperature 80 78 76 74 72 70 68 -20 0 20 40 60 80 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -40 100 -20 0 20 Temperature (°C) 40 60 80 100 Temperature (°C) µH, CD54) AIC1638-30 Load Regulation (L=100µ AIC1638-27 Supply Current vs Temperature 3.1 52 2.0V 3.0 48 2.9 Output voltage VOUT(V) Supply Current IDD1 (uA) 60 1.8 82 66 -40 40 Temperature (°C) 44 40 36 32 28 1.8V 2.7 2.6 2.5 2.4 2.3 1.2V 2.2 VIN=0.9V 2.1 24 2.0 20 -40 1.5V 2.8 -20 0 20 40 60 80 100 Temperature (°C) 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 Output Current (mA) ANALOG INTEGRATIONS CORPORATION www.analog.com.tw 4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C. TEL: (8863)577-2500 FAX:(8863)577-2510 5 AIC1638 3-PIN ONE-CELL STEP-UP DC/DC CONVERTER SPEC NO: DS-1638-00 03/01/00 " TYPICAL PERFORMANCE CHARACTERISTICS (CONTINUED) µH CD54) AIC1638-30 Load Regulation (L=47µ µH, CD54) AIC1638-30 Efficiency (L=100µ 3.1 85 3.0 80 Output Voltage (V) 2.9 Efficiency (%) 75 70 2.0V 1.8V 65 60 50 0 20 60 2.4 2.2 80 100 120 140 160 VIN=0.9V 0 20 40 60 80 100 120 140 160 180 200 220 180 Output Current (mA) Output Current (mA) AIC1638-30 Start-up & Hold-on Voltage (L=100µH) µH CD54) AIC1638-30 Efficiency (L=47µ 85 VIN=2.0V 2.5 1.2V 40 VIN=1.8V 2.6 2.3 VIN=0.9V VIN=1.5V 2.7 1.5V 55 VIN=1.2V 2.8 1.0 Start up 0.9 80 0.8 Input Voltage (V) Efficiency (%) 75 70 65 VIN=2.0V VIN=1.8V 60 55 VIN=1.5V VIN=0.9V 50 0 50 75 0.6 Hold on 0.5 0.4 0.3 0.2 VIN=1.2V 25 0.7 0.1 100 125 150 175 200 225 0.0 0 Output Current (mA) 4 6 8 10 12 14 16 18 20 Output Current (mA) AIC1638-30 Start-up & Hold-on Voltage (L=47uH) AIC1638-30 Output Voltage vs Temperature 3.06 1.0 Start up 0.9 3.04 Output Voltage Vout (V) 0.8 Input Voltage (V) 2 0.7 0.6 0.5 Hold on 0.4 0.3 0.2 No Load 3.02 3.00 2.98 2.96 2.94 2.92 0.1 0.0 0 2 4 6 8 10 12 14 16 18 20 Output Current (mA) 2.90 -40 -20 0 20 40 60 80 100 Temperature (°C) ANALOG INTEGRATIONS CORPORATION www.analog.com.tw 4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C. TEL: (8863)577-2500 FAX:(8863)577-2510 6 AIC1638 3-PIN ONE-CELL STEP-UP DC/DC CONVERTER SPEC NO: DS-1638-00 03/01/00 " TYPICAL PERFORMANCE CHARACTERISTICS (CONTINUED) AIC1638-30 Maximum Duty Cycle vs Temperature 82 140 80 Maximum Duty Cycle (%) Switching Frequency (kHz) AIC1638-30 Switching Frequency vs Temperature 160 120 100 80 60 40 78 76 74 72 70 68 20 0 -40 -20 0 20 40 60 80 66 -40 100 -20 0 1.8 52 1.6 48 Supply Current IDD1 (µA) SW Turn On Resistance (Ω) 40 60 80 100 AIC1638-30 Supply Current vs Temperature AIC1638-30 SW On Resistance vs Temperature 1.4 1.2 1.0 0.8 0.6 0.4 44 40 36 32 28 24 0.2 0.0 -40 20 Temperature (°C) Temperature (°C) -20 0 20 40 60 80 20 -40 100 -20 0 20 40 60 80 100 Temperature (°C) Temperature (°C) AIC1638-33 Load Regulation (L=100µH, CD54) AIC1638-33 Efficiency (L=100µH, CD54) 90 3.4 VIN=2.0V 3.3 85 3.1 80 VIN=1.8V VIN=1.5V Efficiency (%) Output Voltage (V) 3.2 3.0 2.9 VIN=1.2V 2.8 2.7 2.6 VIN=2.0V 75 70 VIN=1.8V 65 60 VIN=1.2V 2.5 VIN=0.9V 2.4 2.3 55 50 0 25 50 75 100 125 150 175 200 Output Current (mA) VIN=1.5V VIN=0.9V 0 25 50 75 100 125 150 175 200 Output Current (mA) ANALOG INTEGRATIONS CORPORATION www.analog.com.tw 4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C. TEL: (8863)577-2500 FAX:(8863)577-2510 7 AIC1638 3-PIN ONE-CELL STEP-UP DC/DC CONVERTER SPEC NO: DS-1638-00 03/01/00 " TYPICAL PERFORMANCE CHARACTERISTICS (CONTINUED) AIC1638-33 Efficiency (L=47µH,CD54) 90 3.3 85 3.2 80 3.1 VIN=2.0V VIN=1.8V VIN=1.5V Efficiency (%) Output Voltage (V) AIC1638-33 Load Regulation (L=47µH, CD54) 3.4 3.0 2.9 2.8 2.7 70 65 60 55 VIN=1.2V VIN=0.9V 2.5 25 50 VIN=1.2V 45 40 0 75 100 125 150 175 200 225 0 25 50 75 150 175 200 225 250 3.50 1.1 3.45 1.0 Output Voltage Vout (V) Start up 0.9 Input Voltage (V) 125 AIC1638-33 Output Voltage vs Temperature AIC1638-33 Start-up & Hold-on Voltage (L=100µH) 0.8 0.7 0.6 0.5 Hold on 0.4 0.3 0.2 No Load 3.40 3.35 3.30 3.25 3.20 3.15 3.10 3.05 0.1 0 2 4 6 8 10 12 14 16 18 20 3.00 -40 -20 0 20 40 60 80 100 Temperature (°C) Output Current (mA) AIC1638-33 Switching Frequency vs Temperature AIC1638-33 Maximum Duty Cycle vs Temperature 150 82 140 80 Maximum Duty Cycle (%) Switching Frequency (kHz) 100 Output Current (mA) Output Current (mA) 0.0 VIN=1.8V VIN=1.5V VIN=0.9V 50 2.6 2.4 VIN=2.0V 75 130 120 110 100 90 80 70 78 76 74 72 70 68 60 50 -40 -20 0 20 40 60 80 100 Temperature (°C) 66 -40 -20 0 20 40 60 80 100 Temperature (°C) ANALOG INTEGRATIONS CORPORATION www.analog.com.tw 4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C. TEL: (8863)577-2500 FAX:(8863)577-2510 8 AIC1638 3-PIN ONE-CELL STEP-UP DC/DC CONVERTER SPEC NO: DS-1638-00 03/01/00 " TYPICAL PERFORMANCE CHARACTERISTICS (CONTINUED) AIC1638-33 Supply Current vs Temperature 60 1.6 56 Supply Current IDD1 (µA) SW Turn On Resistance (Ω) AIC1638-33 SW On Resistance vs Temperature 1.8 1.4 1.2 1.0 0.8 0.6 0.4 52 48 44 40 36 32 28 0.2 0.0 -40 -20 0 20 40 60 80 24 -40 100 -20 0 20 Temperature (°C) 5.0 90 4.0 VIN=1.5V 3.0 70 100 VIN=3.0V VIN=2.0V 60 VIN=0.9V VIN=1.5V 50 VIN=1.2V VIN=1.2V 40 2.5 VIN=0.9V 2.0 1.5 80 80 VIN=3.0V VIN=2.0V Efficiency (%) Output Voltage (V) 5.5 100 3.5 60 AIC1638-50 Efficiency (L=100µH,CD54) AIC1638-50 Load Regulation ( L=100µH,CD54) 4.5 40 Temperature (°C) 30 0 50 100 150 200 250 300 350 20 400 0 50 100 150 200 250 300 350 400 Output Current (mA) Output Current (mA) AIC1638-50 Efficiency (L=47µH,CD54) AIC1638-50 Load Regulation (L=47µH,CD54) 90 5.5 85 5.0 Efficiency (%) Output Voltage (V) 80 VIN=3.0V 4.5 VIN=2.0V 4.0 3.5 VIN=1.5V 3.0 VIN=1.2V 2.5 70 VIN=3.0V 65 60 VIN=2.0V 55 VIN=0.9V 2.0 1.5 75 VIN=0.9V 50 0 50 100 150 200 250 300 350 400 Output Current (mA) 45 0 50 VIN=1.5V VIN=1.2V 100 150 200 250 300 350 400 Output Current (mA) ANALOG INTEGRATIONS CORPORATION www.analog.com.tw 4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C. TEL: (8863)577-2500 FAX:(8863)577-2510 9 AIC1638 3-PIN ONE-CELL STEP-UP DC/DC CONVERTER SPEC NO: DS-1638-00 03/01/00 " TYPICAL PERFORMANCE CHARACTERISTICS (CONTINUED) AIC1638-50 Output Voltage vs Temperature AIC1638-50 Start-up & Hold-on Voltage (L=100µH) 5.3 1.8 5.2 Output Voltage Vout (V) 1.6 Input Voltage (V) 1.4 1.2 1.0 Start up 0.8 0.6 Hold on 0.4 5.0 4.9 4.8 4.7 4.6 4.5 0.2 0.0 No Load 5.1 0 2 4 6 8 10 12 14 16 18 4.4 -40 20 -20 0 Output Current (mA) 100 80 Maximum Duty Cycle (%) Switching Frequency (kHz) 80 82 140 130 120 110 100 90 80 78 76 74 72 70 68 66 70 -20 0 20 40 60 80 64 -40 100 -20 0 Temperature (°C) 20 40 60 80 100 Temperature (°C) AIC1638-50 Supply Current vs Temperature AIC1638-50 SW On Resistance vs Temperature 100 1.6 90 1.4 Supply Current IDD1 µA) SW Turn On Resistance (Ω) 60 AIC1638-50 Maximum Duty Cycle vs Temperature AIC1638-50 Switching Frequency vs Temperature 150 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -40 40 Temperature (°C) 60 -40 20 80 70 60 50 40 30 20 -20 0 20 40 60 80 100 Temperature (°C) 10 -40 -20 0 20 40 60 80 100 Temperature (°C) ANALOG INTEGRATIONS CORPORATION www.analog.com.tw 4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C. TEL: (8863)577-2500 FAX:(8863)577-2510 10 AIC1638 3-PIN ONE-CELL STEP-UP DC/DC CONVERTER SPEC NO: DS-1638-00 03/01/00 " TYPICAL PERFORMANCE CHARACTERISTICS (CONTINUED) VOUT 20mv/div VOUT 50mV/div VIN 0.5V/div Load Step 50mA/div Load Transient Response Line Transient Response (L=100µH, Co=47µF, VIN=2V) BLOCK DIAGRAM SW 1.25V REF. VOUT 1M + Enable GND OSC, 100KHz PIN DESCRIPTIONS PIN1 : GND - Ground. Must be low impedance; sorder directly to ground plane. PIN2 : VOUT - IC supply pin. Connect VOUT to the regulator output. APPLICATION INFORMATION GENERAL DESCRIPTION AIC1638 PFM (pulse frequency modulation) controller ICs combine a switch mode regulator, N-channel power MOSFET, precision voltage reference, and voltage detector in a single monolithic device. They offer both extreme low quiescent current, high efficiency, and very low gate threshold voltage to PIN3 : SW – Internal drain of N-MOSFET switch. ensure start-up with low battery voltage ( 0.8V typ.). Designed to maximize battery life in portable products, and minimize switching losses by only switching as needed service the load. PFM controllers transfer a discrete amount of energy per cycle and regulate the output voltage by modulating switching frequency with the constant ANALOG INTEGRATIONS CORPORATION www.analog.com.tw 4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C. TEL: (8863)577-2500 FAX:(8863)577-2510 11 AIC1638 3-PIN ONE-CELL STEP-UP DC/DC CONVERTER SPEC NO: DS-1638-00 03/01/00 turn-on time. 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 1.5 Ω to minimize switch losses. When the output voltage drops, the error comparator enables 100KHz oscillator that turns on the MOSFET around 7.5us and 2.5µs off time. Turning on the MOSFET allows inductor current to ramp up, storing energy in a magnetic field. When MOSFET turns off that force inductor current through diode to the output capacitor and load. As the stored energy is depleted, the current ramp down until the diode turns off. At this point, inductor may ring due to residual energy and stray capacitance. The output capacitor stores charge when current flowing through the diode is high, and release 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 ensure adequate time for energy transfer to output during the second half each cycle. Depending on circuit, PFM controller can 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 IIN IPK ISW ID VSW Charge Co. IOUT TDIS Discharge Co. t Discontinuous Conduction Mode VEXT IIN ID IOUT IIN SW + EXT VEXT IPK VOUT IV Isw Ico ISW ID IOUT VSW t Continuous Conduction Mode ANALOG INTEGRATIONS CORPORATION www.analog.com.tw 4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C. TEL: (8863)577-2500 FAX:(8863)577-2510 12 AIC1638 3-PIN ONE-CELL STEP-UP DC/DC CONVERTER SPEC NO: DS-1638-00 03/01/00 At the boundary between continuous and discontinuous mode, output current (IOB) is determined by VIN 1 VIN IOB = TON(1− x ) 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 mode, the switching frequency (fsw) is fsw = 2(L)(VOUT + VD − VIN)(IOUT) (1+ x VIN 2 × TON 2 In the continuous mode, the switching frequency is fsw = 1 (VOUT + VD − VIN) [1+ x ( TON (VOUT + VD − VSW) ≅ VIN − VSW )] 2 VOUT + VD − VSW 1 VOUT + VD − VIN TON VOUT + VD − VSW where Vsw = switch drop and proportion to output current. INDUCTOR SELECTION Ron + Rs Vin IPK = Ton) 1 − exp( − L Ron + Rs x VIN ≅ (TON)1 − 2 L VIN (Simple losses equation), ≅ TON L where x=(RON+RS)TON/L 1 EL = L × Ipk2 2 Power required from the inductor per cycle must be equal or greater than 1 PL/fSW = (VOUT + VD − VIN)(IOUT)( ) fSW in order for the converter to regulate the output. When loading is over IOB, PFM controller operates in continuous mode. Inductor peak current can be derived from VOUT + VD − VSW x − IOUT + IPK = VIN − VSW 2 x VIN − VSW TON1 − 2L 2 Valley current (Iv) is VOUT + VD − VSW x VIN − VSW Iv = − IOUT − × − IN SW 2L 2 V V x TON1− 2 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 inductance must also be high enough so maximum current rating of AIC1638 and inductor are not exceed 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. But unfortunately this is inversely related to physical size. Minimum and Maximum input voltage, output voltage and output current must be established before and 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 ANALOG INTEGRATIONS CORPORATION www.analog.com.tw 4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C. TEL: (8863)577-2500 FAX:(8863)577-2510 13 AIC1638 3-PIN ONE-CELL STEP-UP DC/DC CONVERTER SPEC NO: DS-1638-00 03/01/00 Table 1 Indicates resistance and height for each coil. Power Inductor Type DS1608 Coilcraft SMT Type (www.coilcraft.com) Inductance ( µH ) Resistance (Ω) Rated Current (A) 22 0.10 0.7 47 0.18 0.5 100 0.38 0.3 22 0.08 2.7 47 0.14 1.8 47 0.25 0.7 100 0.50 0.5 47 0.25 0.7 100 0.50 0.5 33 0.11 1.2 Height (mm) DO3316 Sumida SMT Type CD54 Hold SMT Type PM54 Hold SMT Type PM75 2.9 5.2 4.5 4.5 5.0 CAPACITOR SELECTION DIODE SELECTION A poor choice for a output capacitor can result in Speed, forward drop, and leakage current are the poor efficiency and high output ripple. Ordinary three main consideration in selecting a rectifier aluminum electrolytic, while inexpensive may have diode. Best performance is obtained with Schottky unacceptably poor ESR and ESL. There are low rectifier diode such 1N5819. Motorola makes ESR aluminum capacitors for switch mode DC-DC MBR0530 in surface mount. For lower output power converters which work much better than general a 1N4148 can be used although efficiency and propose unit. Tantalum capacitors provide still better start-up voltage will suffer substantially. performance at more expensive. OS-CON capacitors have extremely low ESR in a small size. If capacitance is reduced, output ripple will increase. COMPONENT POWER DISSIPATION Operating in discontinuous mode, power loss in the Most of the input supply is supplied by the input winding resistance of inductor can be approximate bypass capacitor, the capacitor voltage rating equal to should be at least 1.25 times greater than a maximum input voltage. PDL = 2 TON VOUT + VD (Rs ) (POUT ) 3 L VOUT where POUT=VOUT * IOUT ; Rs=Inductor DC R; ANALOG INTEGRATIONS CORPORATION www.analog.com.tw 4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C. TEL: (8863)577-2500 FAX:(8863)577-2510 14 AIC1638 3-PIN ONE-CELL STEP-UP DC/DC CONVERTER SPEC NO: DS-1638-00 03/01/00 VD = Diode drop. The power dissipated in rectifier diode is The power dissipated in a switch loss is VD PDD = (POUT) VOUT PDsw = 2 TON VOUT + VD − VIN (RON) (POUT ) 3 L VOUT PHYSICAL DIMENSION ! SOT-89 (unit: mm) D A SYMBOL MIN MAX C A 1.40 1.60 B 0.36 0.48 C 0.35 0.44 D 4.40 4.60 D1 1.62 1.83 E 2.29 2.60 D1 H E L B e e1 e 1.50 (TYP.) e1 3.00 (TYP.) H 3.94 4.25 L 0.89 1.20 SYMBOL MIN MAX A 4.32 5.33 SOT-89 MARKING Part No. AIC1638-27 AIC1638-30 AIC1638-33 AIC1638-50 Marking AN27 AN30 AN33 AN50 ! TO-92 (unit: mm) A E L C C e1 D 0.38 (TYP.) D 4.40 5.20 E 3.17 4.20 e1 L 1.27 (TYP.) 12.7 ANALOG INTEGRATIONS CORPORATION www.analog.com.tw 4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C. TEL: (8863)577-2500 FAX:(8863)577-2510 - 15