AIC1578 High-Efficiency, Step-Down DC/DC Converter FEATURES DESCRIPTION • 4V to 20V Input Voltage Operation. • High Efficiency (up to 95%). The AIC1578 is a high performance step-down DC/DC converter, designed to drive an external P-channel MOSFET to generate programmable output voltages. Two main schemes of PulseSkipping and Pulse-Frequency Modulation are employed to maintain low quiescent current and high conversion efficiency under wide ranges of input voltage and loading condition. The AIC1578 delivers 10mA to 2A of output current with 87%~93% efficiency at VIN=9V, VOUT=5V condition. A current sense comparator with both inverting and non-inverting input uncommitted is included to provide the crucial function of either current limit protection or constant output current control. When the AIC1578 is used in a high-side current sensing step-down constant current source, the efficiency is typically greater than 90%. Duty cycle can be adjusted to greater than 90% by connecting a resistor from DUTY pin to VIN. Quiescent current is about 90µA and can be reduced to 8µA in shutdown mode. Switching frequency being in around 90KHz to 280KHz range, small size switching components are ideal for battery powered portable equipment. • Low Quiescent Current at 90µA. • Pulse-Skipping and Pulse-Frequency Modulation. • Inputs-Uncommitted Current Sense Comparator. • Duty Cycle Adjustable. • 90KHz to 280KHz Oscillator Frequency. • Power-Saving Shutdown Mode (8µA Typical). • Push-Pull Driver Output. APPLICATIONS • Notebook 5V/3.3V Main Power • Step-Down DC/DC Converter Module. • Constant Current Source for Battery Chargers. TYPICAL APPLICATION CIRCUIT **RS * L1 33µH D1 1N5820 Q1 C3 220µF + + C4 C2 R2 1M 1M Control *Sumida MPP CORE VIN CS+ DUTY CS - SHDN DRI Battery + 0.1µF C1 100µF D2 RDUTY 1N5820 IRF9Z34 10µF VIN GND FB AIC1578 **Charge current=57mV/RS Constant Current Source for Battery Charger ORDERING INFORMATION AIC1578 XX ORDER NUMBER PACKAGE TYPE N: PLASTIC DIP S: SMALL OUTLINE TEMPERATURE RANGE C: 0°C~+70°C AIC1578CN (PLASTIC DIP) AIC1578CS (PLASTIC SO) PIN CONFIGURATION TOP VIEW VIN 1 8 CS+ DUTY 2 7 CS- SHDN 3 6 DRI FB 4 5 GND Analog Integrations Corporation 4F, 9, Industry E. 9th Rd, Science Based Industrial Park, Hsinchu Taiwan, ROC DS-1578-02 TEL: 886-3-5772500 Dec 27, 00 FAX: 886-3-5772510 www.analog.com.tw 1 AIC1578 ABSOLUTE MAXIMUM RATINGS VIN Supply Voltage .....…………............................................................................. 20V DUTY Voltage .........................................……………................................................ 20V SHDN Voltage ......................................………….................................................... 15V ................…………......................................... 0°C~70°C Operating Temperature Range Storage Temperature Range ......................…………................................. -65°C~ 150°C TEST CIRCUIT Refer to Fig. 1 circuit of Application Examples. ELECTRICAL CHARACTERISTICS (VIN= 13V, Ta=25°°C, unless otherwise specified.) PARAMETERS CONDITIONS Operation Voltage MIN. TYP. 4 MAX. UNIT 20 V Quiescent Current VFB = 1.5V 90 160 µA Shutdown Mode Current V SHDN = 0V 8 20 µA 1.22 1.28 V Internal Reference Voltage 1.16 Driver Sinking "ON Resistance" 16 Ω Driver Sourcing "ON Resistance" 11 Ω Current Limit Sense Threshold VCS+ = 13V Shutdown Threshold 50 70 90 mV 0.8 1.5 2.4 V 1 µA SHDN Pin Leakage Current V SHDN < 15V Duty Cycle VDUTY = VIN 71 % Oscillator Frequency VDUTY = VIN 225 KHz 2 AIC1578 TYPICAL PERFORMANCE CHARACTERISTICS Duty 80 Duty (%) Frequency 90 30 85 25 75 20 70 15 65 10 60 50 55 4 6 8 10 12 14 16 18 Duty Cycle vsTemperature VIN=5V Duty Cycle (%) Ta = 27°C 85 35 Frequency (KHz) Frequency & Duty Cycle vs VIN 90 80 75 VIN=13V 70 VIN=20V 65 60 0 20 0 VIN ( V) 20 40 Temperature (°C) 60 80 Duty Cycle vs RDUTY Frequency vs Temperature 10 VIN=5V VIN=20V 90 Duty Cycle (%) Frequency (KHz) 290 240 VIN=13V 190 140 80 VIN=10V VIN=15V 70 VIN=5V VIN=20V RDUTY refer to Typ. App. 90 0 10 20 30 40 50 60 60 0 70 1 Temperature (°C) Shutdown Current vs VIN 15 4 Quiescent Current vs VIN Ta=25°C Ta=0°C 10 Ta=70°C 5 0 3 11 Quiescent Current (µA) Shutdown Current (µA) 20 2 RDUTY (MΩ) 4 6 8 10 12 VIN (V) 14 16 18 20 Ta= 0°C 100 90 Ta= 25°C 80 Ta= 70°C 70 60 4 6 8 10 12 VIN (V) 14 16 18 20 3 AIC1578 BLOCK DIAGRAM Current Limit Comparator VIN 1 70mV DUTY SHDN 2 3 PFM OSC VIN LATCH + FB CS+ CS- DRI Error Comparator 4 1.22V Reference Voltage Output Driver PIN 3: SHDN- Logical input to shutdown the chip: V SHDN = High for normal operation. V SHDN = Low for shutdown. This pin should not be floating or forced to greater than 15V. In shutdown mode DRI pins is at high level. - Feedback comparator input, to compare the feedback voltage with the internal reference 5 GND voltage. Connecting a resistor R1 to converter output node and a resistor R2 to ground yields the output voltage: - 4V to 20V input supply voltage. PIN 2: DUTY - Duty cycle adjustment pin. To be tied to the VIN pin directly or through a resistor RDUTY to adjust oscillator duty cycle. RDUTY must be above 1MΩ if VIN=20V. See TYPICAL PERFORMANCE CHARACTERISTICS. PIN 4: FB 7 6 PIN DESCRIPTIONS PIN 1: VIN 8 + VOUT=1.22 ×(R1+R2)/ R2 PIN 5: GND - Power ground. PIN 6: DRI - Push-pull driver output to drive an external P-channel MOSFET or PNP transistor. When driving a PNP bipolar transistor, a base resistor and a capacitor to the base of PNP are recommended. PIN 7: CS- - Current sense comparator inverting input, not to exceed VIN voltage. PIN 8: CS+ - Current sense comparator noninverting input, not to exceed VIN voltage. 4 AIC1578 APPLICATION EXAMPLES Efficiency vs Load Current 100 IRF9Z34 Q1 FB *L1 GND 15.4K + 300µF C3 1N5820 D1 R2 VOUT 33µH Efficiency (%) CS+ DUTY CSAIC1578 DRI SHDN 5V 95 5V/2A VIN C2 100µF 0.1µF VOUT=5V VIN + C1 6.4 ~ 20V 90 VIN=6.4 V 85 VIN=9V VIN=16 V 8010 R1 *:Sumida MPP Core 47K 100 1000 Load Current (mA) Fig. 1 5V Step-Down Converter Efficiency vs Load Current 95 5V FB + C1 VIN 6 ~ 20V *L1 GND 1N5820 D1 R2 R1 27.4K 47K VOUT 33µH 300µF C3 + VIN=6V 90 Efficiency (%) IRF9Z34 Q1 CSDUTY AIC1578 DRI SHDN 100µF CS+ C2 3.3V/2A VIN 0.1µF VOUT=3.3V 85 VIN=9V 80 VIN=16V 75 *:Sumida MPP Core 10 10 Load Current (mA) 1000 Fig. 2 3.3V Step-Down Converter 5 + C2 0.1µF 100µF C1 D1 1N5820 Q1 R13 C3 RDUTY VIN DUTY 1M 1M SHDN R5 FB 1M D3 + 220µF RS C4 + 10µF CS+ CSDRI GND AIC1578 220 R9 VBATT D2 R10 1.5K C7 100µF R6 390K R8 + VBT + 150K C6 C5 R7 150K 0.1µF VIN *L1 1N5820 4.7µF IRF9Z34 33µH BATTERY 1K 1M GND C8 0.1µF Fast Charge 1N4148 R4 Trickle Charge AIC1578 R11 1.5K VREF VDD TIMER VOUT MODE LED AIC1761/1766 R12 *:Sumida MPP Core RS =0.1Ω, charge current =0.5A ±10%, VIN>VBATT +3.5V RS =0.05Ω, charge current =1A±10%, VIN>VBATT +4V RS =0.033Ω, charge current =1.5A ±10%, VIN>VBATT +4.5V Efficiency>90%, measured at CS- node NOTE: Fig. 3 Battery Charge Circuit with High-Side Current Sensing Constant Current Source PHYSICAL DIMENSIONS 8 LEAD PLASTIC SO (unit: mm) D H E e A B SYMBOL MIN MAX A 1.35 1.75 A1 0.10 0.25 B 0.33 0.51 C 0.19 0.25 D 4.80 5.00 E 3.80 4.00 e C A1 L 1.27(TYP) H 5.80 6.20 L 0.40 1.27 6 AIC1578 8 LEAD PLASTIC DIP (unit: mm) D E1 E A2 A1 C L eB b e SYMBOL MIN MAX A1 0.381 — A2 2.92 4.96 b 0.35 0.56 C 0.20 0.36 D 9.01 10.16 E 7.62 8.26 E1 6.09 7.12 e 2.54 (TYP) eB — 10.92 L 2.92 3.81 7