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| AIC1578 High-Efficiency, Step-Down DC/DC Converter FEATURES * 4V to 20V Input Voltage Operation. * High Efficiency (up to 95%). * Low Quiescent Current at 90A. * Pulse-Skipping and Pulse-Frequency Modulation. * Inputs-Uncommitted Current Sense Comparator. * Duty Cycle Adjustable. * 90KHz to 280KHz Oscillator Frequency. * Power-Saving Shutdown Mode (8A Typical). * Push-Pull Driver Output. DESCRIPTION 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 90A and can be reduced to 8A in shutdown mode. Switching frequency being in around 90KHz to 280KHz range, small size switching components are ideal for battery powered portable equipment. APPLICATIONS * Notebook 5V/3.3V Main Power * Step-Down DC/DC Converter Module. * Constant Current Source for Battery Chargers. TYPICAL APPLICATION CIRCUIT VIN IRF9Z34 Q1 * L1 33H D1 1N5820 C3 220F + C4 10F **RS + D2 100F + 0.1F C2 RDUTY R2 1M 1M Control *Sumida MPP CORE VIN DUTY SHDN FB AIC1578 **Charge current=57mV/RS CS+ CS DRI GND Battery C1 Constant Current Source for Battery Charger ORDERING INFORMATION AIC1578 XX PACKAGE TYPE N: PLASTIC DIP S: SMALL OUTLINE TEMPERATURE RANGE C: 0C~+70C 1N5820 ORDER NUMBER AIC1578CN (PLASTIC DIP) PIN CONFIGURATION TOP VIEW VIN DUTY 1 2 3 4 8 CS+ 7 CS6 DRI 5 GND AIC1578CS (PLASTIC SO) SHDN FB Analog Integrations Corporation DS-1578-02 Dec 27, 00 4F, 9, Industry E. 9th Rd, Science Based Industrial Park, Hsinchu Taiwan, ROC TEL: 886-3-5772500 FAX: 886-3-5772510 www.analog.com.tw 1 AIC1578 ABSOLUTE MAXIMUM RATINGS VIN Supply Voltage DUTY Voltage .............................................................................................. 20V ........................................................................................................ 20V ...................................................................................................... 15V SHDN Voltage Operating Temperature Range Storage Temperature Range ..................................................................... 0C~70C ................................................................... -65C~ 150C TEST CIRCUIT Refer to Fig. 1 circuit of Application Examples. ELECTRICAL CHARACTERISTICS (VIN= 13V, Ta=25C, unless otherwise specified.) PARAMETERS CONDITIONS MIN. TYP. MAX. UNIT Operation Voltage Quiescent Current Shutdown Mode Current Internal Reference Voltage Driver Sinking "ON Resistance" Driver Sourcing "ON Resistance" Current Limit Sense Threshold Shutdown Threshold SHDN Pin Leakage Current Duty Cycle Oscillator Frequency V SHDN < 15V VDUTY = VIN VDUTY = VIN VCS+ = 13V VFB = 1.5V V SHDN = 0V 4 90 8 1.16 1.22 16 11 50 0.8 70 1.5 20 160 20 1.28 V A A V 90 2.4 1 mV V A 71 225 % KHz 2 AIC1578 TYPICAL PERFORMANCE CHARACTERISTICS 90 85 80 Frequency & Duty Cycle vs VIN Ta = 27C Duty Frequency 35 30 25 20 15 10 50 0 20 90 85 Duty Cycle vsTemperature Frequency (KHz) VIN=5V Duty Cycle (%) 80 75 70 65 60 0 20 Duty (%) 75 70 65 60 55 4 VIN=13V VIN=20V 6 8 10 12 14 16 18 VIN ( V) Temperature (C) 40 60 80 Frequency vs Temperature 10 290 Duty Cycle vs RDUTY VIN=5V VIN=20V Frequency (KHz) 90 240 Duty Cycle (%) 190 VIN=13V 80 VIN=10V VIN=15V 140 VIN=5V 70 VIN=20V RDUTY refer to Typ. App. 90 0 10 20 30 40 50 60 70 60 0 1 Temperature (C) RDUTY (M) 2 3 4 20 Shutdown Current vs VIN 11 Quiescent Current vs VIN Shutdown Current (A) Ta=25C Ta=0C Quiescent Current (A) 15 100 Ta= 0C 90 10 Ta= 25C 80 Ta= 70C 5 Ta=70C 70 0 4 6 8 10 12 14 16 18 20 60 4 6 8 10 VIN (V) VIN (V) 12 14 16 18 20 3 AIC1578 BLOCK DIAGRAM Current Limit Comparator VIN 1 + 70mV 8 CS+ DUTY 2 PFM OSC LATCH VIN 7 CS- SHDN 3 + Error Comparator 1.22V Reference Voltage Output Driver 6 DRI FB 4 5 GND PIN DESCRIPTIONS PIN 1: VIN - 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 1M if VIN=20V. See TYPICAL PERFORMANCE CHARACTERISTICS. PIN 3: SHDN- Logical input to shutdown the chip: VSHDN = High for normal operation. VSHDN = Low for shutdown. This pin should not be floating or forced to greater than 15V. In shutdown mode DRI pins is at high level. PIN 4: FB - Feedback comparator input, to compare the feedback voltage with the internal reference voltage. Connecting a resistor R1 to converter output node and a resistor R2 to ground yields the output voltage: VOUT=1.22 x(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. - Current sense comparator inverting input, not to exceed VIN voltage. PIN 7: CS- PIN 8: CS+ - Current sense comparator noninverting input, not to exceed VIN voltage. 4 AIC1578 APPLICATION EXAMPLES Efficiency vs Load Current 100 VOUT=5V C2 100F 0.1F VIN + C1 6.4 ~ 20V 95 VIN CS+ IRF9Z34 Q1 Efficiency (%) 5V DUTY CSAIC1578 DRI SHDN FB GND 90 VIN=6.4 V VIN=9V 33H *L1 + VOUT 5V/2A 1N5820 D1 R2 15.4K R1 47K 300F C3 85 VIN=16 V 100 1000 80 10 *:Sumida MPP Core Load Current (mA) Fig. 1 5V Step-Down Converter Efficiency vs Load Current VOUT=3.3V 0.1F C2 100F + C1 VIN 6 ~ 20V 90 95 VIN=6V VIN 5V CSDUTY AIC1578 DRI SHDN FB GND IRF9Z34 Q1 Efficiency (%) CS+ 85 33H *L1 300F C3 + VOUT 3.3V/2A VIN=9V 80 1N5820 D1 R2 27.4K R1 47K VIN=16V 75 10 10 1000 *:Sumida MPP Core Load Current (mA) Fig. 2 3.3V Step-Down Converter 5 AIC1578 R4 IRF9Z34 VIN Q1 1K D1 1N5820 33H *L1 C3 1N4148 D3 + 220F RS 1N5820 D2 BATTERY VBATT R6 390K R8 4.7F + 150K C6 C5 R7 150K 1M R12 0.1F Trickle Charge 220 R9 C7 100F + R10 1.5K C8 0.1F Fast Charge C4 + 10F R11 1.5K C1 + 0.1F C2 R13 1M RDUTY VIN DUTY 1M 1M SHDN R5 FB 100F CS+ CSDRI GND VBT GND TIMER MODE VREF VDD VOUT LED AIC1578 AIC1761/1766 *:Sumida MPP Core NOTE: RS =0.1, charge current =0.5A 10%, VIN>VBATT +3.5V RS =0.05, charge current =1A10%, VIN>VBATT +4V RS =0.033, charge current =1.5A 10%, VIN>VBATT +4.5V Efficiency>90%, measured at CS- node Fig. 3 Battery Charge Circuit with High-Side Current Sensing Constant Current Source PHYSICAL DIMENSIONS 8 LEAD PLASTIC SO (unit: mm) D SYMBOL A H E MIN 1.35 0.10 0.33 0.19 4.80 3.80 MAX 1.75 0.25 0.51 0.25 5.00 4.00 A1 B C e A C A1 D E e H L 1.27(TYP) 5.80 0.40 6.20 1.27 B L 6 AIC1578 8 LEAD PLASTIC DIP (unit: mm) D SYMBOL A1 E1 MIN 0.381 2.92 0.35 0.20 9.01 7.62 6.09 MAX -- 4.96 0.56 0.36 10.16 8.26 7.12 A2 b E C D E C A2 A1 L E1 e eB L eB b e 2.54 (TYP) -- 2.92 10.92 3.81 7 |
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