AIC2352 700mA Synchronous PWM/PSM Step-Down DC/DC Converter FEATURES 2.5V to 5.5V Input Voltage Range 700mA Guaranteed Output Current Up to 95% Efficiency Low RDS(ON) Internal Switche: 280mΩ No Schottky Diode Required 100% Duty Cycle in Low Dropout Operation Operating Frequency: 1.5MHz Accurate Reference 0.6V Provides Low Output Voltages APPLICATIONS LCD TV Multi-function Peripheral Cellular Phones CPU I/O Supplies Cordless Phones PDAs and Handy-Terminals Battery-Operated Devices (1 Li-Ion or 3 NiMH/ NiCd) DESCRIPTION The AIC2352 is a low-noise, pulse-widthmodulated (PWM), DC-DC step-down converter. The device is available in an adjustable version and fixed output voltages of 1.0V, 1.2V, 1.8V, and 3.3V. The device features an internal synchronous rectifier for high efficiency; it requires no external Schottky diode. The AIC2352 is ideally suited for Li-Ion battery applications. PWM/PSM mode extends battery life by switching to a pulseskipping-modulated mode during light loads. Shutdown mode places the device in standby, reducing supply current to under 1µA. Other features of the AIC2352 include high efficiency, low dropout voltage, short circuit protection, over temperature protection, and over voltage protection. It is available in a small 5 pins SOT-23 package. APPLICATIONS CIRCUIT Fig. 1 Fixed Step-Down DC/DC Converter Analog Integrations Corporation Si-Soft Research Center DS-2352G-01 20110118 3A1, No.1, Li-Hsin Rd. I , Science Park , Hsinchu 300, Taiwan , R.O.C. TEL: 886-3-5772500 FAX: 886-3-5772510 www.analog.com.tw 1 AIC2352 Fig. 2 Adjustable Step-Down DC/DC Converter ORDERING INFORMATION AI C2352 -XX X X X XX P IN CO NFIG URA TIO N P ACK ING TY PE TR: T APE & REE L B G: BA G TOP VIEW SOT-23-5 V IN VO U T 4 5 P ACK AG E TYP E V 5: S O T-2 3-5 1 G : G reen Package O UTP UT VO LTA G E DE FA ULT: Adj. 10: 1.0V 1 2: 1 .2V 1 8: 1 .8V 3 3: 3 .3V AIC2 352-3 3G V5TR 3.3 V O utp ut V ers ion , 3 EN GN D LX T OP V IEW Fixed versio n SOT-23-5 VIN FB 4 5 1 Exam ple: 2 2 3 EN G ND L X A djusta ble ve rsion in S OT-23 -5 G re en P ac kage & Tape & Re el Packin g Type AIC2 352G V 5TR Ad justa ble Vers io n, in S OT-23 -5 G re en P ac kage & Tape & Re el Packin g Type 2 AIC2352 ORDERING INFORMATION (Continuous) Marking (Fixed Version) Part No. Marking AIC2352-10GV5 HN10G AIC2352-12GV5 HN12G AIC2352-18GV5 HN18G AIC2352-33GV5 HN33G Marking (Adjustable Version) Part No. Marking AIC2352GV5 2352G 3 AIC2352 ABSOLUTE MAXIMUM RATINS VIN, LX Voltage 6V EN, FB Pin Voltage -0.3 V to VIN Operating Ambient Temperature Range TA -40C to 85C Operating Maximum Junction Temperature TJ Storage Temperature Range TSTG 150C -65C to 150C 260C Lead Temperature (Soldering 10 Sec.) Thermal Resistance Junction to Case SOT-23-5 115C/W Thermal Resistance Junction to Ambient SOT-23-5 250C/W (Assume no Ambient Airflow, no Heatsink) Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. 4 AIC2352 ELECTRICAL CHARACTERISTICS (TA=25C, VIN=3.6V unless otherwise specified.) (Note 1) PARAMETER CONDITIONS SYMBOL MIN VIN Output Adjustment Range Reference Voltage Input Voltage Range TYP MAX UNITS 2.5 5.5 V VOUT 0.6V VIN-0.3V V VREF 0.588 0.612 V IFB -50 50 nA 0.6 FB Input Current VFB = VIN P-Channel On-Resistance IOUT = 0.2A PRDS(ON) 280 390 m N-Channel On-Resistance IOUT = 0.2A NRDS(ON) 250 390 m LX Leakage Current VLX=0V or VLX=3.6V 1 uA Peak Inductor Current VIN = 5V IPK Quiescent Current IOUT = 0mA, VFB=VREF + 5% IQ 65 85 A Shutdown Supply Current EN = GND ISHDN 0.1 1 A EN High-Level Input Voltage VIN=2.5V to 5.5V VEN_H EN Low-Level Input Voltage VIN=2.5V to 5.5V VEN_L -1 0.9 1.1 A 1.5 Oscillator Frequency fOSC 1.2 Maximum Duty Cycle DMAX 100 V 1.5 0.4 V 1.8 MHz % Thermal Shutdown Temperature 150 °C Thermal Shutdown Hysteresis 25 °C Note 1: Specifications are production tested at TA=25C. Specifications over the -40C to 85C operating temperature range are assured by design, characterization and correlation with Statistical Quality Controls (SQC). 5 AIC2352 TYPICAL PERFORMANCE CHARACTERISTICS Fig. 3 Efficiency vs. Input Voltage Fig. 4 Efficiency vs. Output Current Fig. 5 Efficiency vs. Output Current Fig. 6 Efficiency vs. Output Current Fig. 7 Output Voltage vs. Temperature Fig. 8 Oscillator Frequency vs. Temperature 6 AIC2352 TYPICAL PERFORMANCE CHARACTERISTICS (Continuous) Fig. 9 Oscillator Frequency vs. Input Voltage Fig. 10 RDS(ON) vs. Input Voltage Fig. 11 Supply Current vs. Input Voltage Fig. 12 Current Limit vs. Input Voltage Fig. 13 Load Transient Response Fig. 14 Load Transient Response 7 AIC2352 TYPICAL PERFORMANCE CHARACTERISTICS (Continuous) Fig. 15 Load Transient Response Fig. 15 Load Transient Response Fig. 17 PSM Operation 8 AIC2352 BLOCK DIAGRAM Functional Block Diagram of AIC2352 PIN DESCRIPTIONS Pin Name Pin Function NC No Internal Connect (Floating or Connecting to GND). EN Chip Enable (Active High). VIN Power Input. LX Pin for Switching. GND Ground. FB/VOUT Feedback/Output Voltage Pin. 9 AIC2352 APPLICATION INFORMATION Operation Short Circuit Protection The AIC2352 is a low-noise step-down DC/DC While the output is shorted to ground, the switching converter control frequency of AIC2352 will be reduced to one third of architecture. It features an internal synchronous the normal switching frequency. This lower switching rectifier, which eliminates the external Schottky diode frequency ensures the inductor current has more time and increases efficiency. During normal operation, the to discharge, thereby preventing inductor current AIC2352 can regulate its output voltage through a runaway. The switching frequency will automatically feedback control circuit, which is composed of an error return to its designed value while short circuit condition amplifier; a current comparator and several control is released. with current-mode PWM/PSM signal generators. By comparing the feedback voltage to the reference voltage of 0.6V, the error amplifier varies its output voltage. The output voltage of the error amplifier is compared with the summing signal of current sensing signal and slope compensation signal to determine the duty cycle of internal main power Shutdown By connecting the EN pin to GND, the AIC2352 can be shut down to reduce the supply current to 0.1A (typical). At this operation mode, the output voltage of step-down converter is equal to 0V. switch (P-channel MOSFET). While the main power 100% Duty Cycle Operation switch is turned on, the synchronous power switch (N- When the input voltage approaches the output voltage, channel MOSFET) will be turned off through anti-short- the AIC2352 smoothly transits to 100% duty cycle through block. Similarly, when the main power switch operation. This allows AIC2352 to regulate the output is turned off, the synchronous power switch will be voltage until AIC2352 completely enters 100% duty turned on until the inductor current starts to reverse or cycle operation. In 100% duty cycle mode, the output the beginning of the next switching cycle. In order to voltage is equal to the input voltage minus the voltage, achieve better efficiency and prevent overcharging the which is the drop across the main power switch. output capacitor, AIC2352 will enter pulse-skipping- The AIC2352 achieves 100% duty cycle operation by modulated mode (PSM) operation while working at extending the turn-on time of the main power switch. If light load conditions. the summing signal of current sensing signal and slope Current Limitation The AIC2352 provides current limit function by using an internal sensing resistor. When the main power switch turns on, current follows through the internal sensing resistor. And current amplifier senses the voltage, which crosses the resistor, and amplifies it. While the sensed voltage gets higher than reference voltage, the current limitation function is activated. While the current limitation function is activated, the duty cycle will be reduced to limit the output power to protect the internal power switches. compensation signal does not reach the output voltage level of the error amplifier at the end of 90% switching period, the main power switch is continuously turned on and the oscillator remains off until the summing signal of current sensing signal and slope compensation signal reaches the output voltage level of the error amplifier. After the summing signal of current sensing signal and slope compensation signal reaches the output voltage level of the error amplifier, the main power switch is turned off and the synchronous power switch is turned on for a constant off time. At the end of the constant off time, the next 10 AIC2352 switching cycle is begun. While the input voltage The selection of output capacitor depends on the approaches required output voltage ripple. The output voltage the output voltage, the switching frequency decreases gradually to smoothly transit to 100% duty cycle operation. If input voltage is very close to output voltage, the ripple can be expressed as: VOUT IL ESR IL 8 fOSC COUT switching mode goes from pure PWM mode to 100% For lower output voltage ripple, the use of low ESR duty cycle operation. During this transient state ceramic capacitor is recommended. The tantalum mentioned above, large output ripple voltage may capacitor can also be used well, but its ERS is larger appear on output terminal. than that of ceramic capacitor. When Components Selection the input and output ceramic capacitors, X5R and X7R types are recommended Inductor The inductor selection depends on the current ripple of inductor, the input voltage and the output voltage. VOUT L fOSC IL choosing because they retain their capacitance over wider ranges of voltage and temperature than other types. Output Voltage Programming (AIC2352 Adjustable Version Only) By connecting a resistive divider R1 and R2, the output V 1 OUT V IN Accepting a large current ripple of inductor allows the voltage of AIC2352 step-down converter can be set. use of a smaller inductance. However, higher current VOUT can be calculated as: ripple of inductor can cause higher output ripple R VOUT 0.6 1 1 R2 voltage and large core loss. By setting an acceptable current ripple of inductor, a suitable inductance can be obtained from above equation. The resistive divider should sit as close to VFB pin as possible. In addition, it is important to ensure the inductor saturation current exceeds the peak value of inductor Layout Consideration current in application to prevent core saturation. The In order to ensure a proper operation of AIC2352, the peak value of inductor current can be calculated following points should be managed comprehensively. according to the following equation. 1. The input capacitor and VIN should be placed as IPEAK IOUT max close as possible to each other to reduce the input VOUT V 1 OUT 2 fOSC L VIN voltage ripple and noise. 2. The output loop, which is consisted of the inductor, Input Capacitor and Output Capacitor To prevent the high input voltage ripple and noise resulted from high frequency switching, the use of low ESR ceramic capacitor for the maximum RMS current is recommended. The approximated RMS current of the input capacitor can be calculated according to the following equation. 2 ICINRMS IOUT (MAX ) the internal main power switch, the internal synchronous power switch and the output capacitor, should be kept as small as possible. 3. The routes with large current should be kept short and wide. 4. Logically the large current on the converter should flow at the same direction. VOUT VIN VOUT 2 VIN IL2 12 5. The VFB pin should be connected to the feedback resistors directly and the route should be away from the noise sources. 11 AIC2352 PHYSICAL DIMENSIONS SOT-23-5 A A E E1 D e e1 SEE VIEW B WITH PLATING c A A2 b SECTION A-A A1 BASE METAL 0.25 S Y M B O L GAUGE PLANE SEATING PLANE L L1 θ VIEW B Note : 1. Refer to JEDEC MO-178AA. 2. Dimension "D" does not include mold flash, protrusions or gate burrs. Mold flash, protrusion or gate burrs shall not exceed 10 mil per side. 3. Dimension "E1" does not include inter-lead flash or protrusions. 4. Controlling dimension is millimeter, converted inch dimensions are not necessarily exact. SOT-23-5 MILLIMETERS MIN. MAX. A 0.95 1.45 A1 0.00 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 L1 θ 0.60 0.60 REF 0° 8° Note: Information provided by AIC is believed to be accurate and reliable. However, we cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AIC product; nor for any infringement of patents or other rights of third parties that may result from its use. We reserve the right to change the circuitry and specifications without notice. Life Support Policy: AIC does not authorize any AIC product for use in life support devices and/or systems. Life support devices or systems are devices or systems which, (I) are intended for surgical implant into the body or (ii) support or sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 12