AIC2351 Low-Noise Synchronous PWM/PFM Step-Down DC/DC Converter FEATURES 2.5V to 5.5V Input Voltage Range 600mA Guaranteed Output Current 95% Efficiency No Schottky Diode Required 30µA Low Quiescent Current 100% Duty Cycle in Low Dropout Operation 1.5MHz Fixed-Frequency PWM Operation Accurate Reference 0.6V Provides Low Output Voltages Small 5-Pin SOT23 Package Internal Soft-Start Function(100μs) DESCRIPTION The AIC2351 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 1.2V, 1.5V, 1.8V, 2.5V, and 3.3V. AIC2351 is capable of delivering continuous 600mA output current over a wide input voltage range from 2.5V to 5.5V. However, it can provide higher peak current. For example, over 1A peak current in the condition of 5V input and 1.2V output. See Fig.13 for detail. The device features an internal synchronous rectifier for high efficiency; it requires no external Schottky diode. Internally fixed-frequency 1.5MHz operation provides easy post-filtering and allows the use of small inductors and capacitors. The AIC2351 is ideally suited for LiIon battery applications. PWM/PFM mode extends battery life by switching to a pulsefrequency-modulated mode during light loads. Shutdown mode places the device in standby, reducing quiescent supply current to under 0.1µA. Other features of the AIC2351 include high efficiency, low dropout voltage, and an accurate reference 0.6V provides low output voltages. It is available in a space-saving 5-pin SOT23 package. APPLICATIONS Cellular Phones CPU I/O Supplies Cordless Phones Notebook Chipset Supplies PDAs and Handy-Terminals Battery-Operated Devices (1 Li-Ion or 3 NiMH/ NiCd). APPLICATIONS CIRCUIT Vin=2.5~5.5V U1 L1 VIN LX Vo=1.8V ON OFF EN VIN Cout 10uF GND OFF EN Vo=2.4V L1 LX 2.2uH R1 273k VFB Cin 4.7uF ON AIC2351-18 R2 91k GND Cout 10uF AIC2351 Fig. 1 Fixed Step-Down DC/DC Converter Analog Integrations Corporation U1 2.2uH VOUT Cin 4.7uF Vin=3.0~5.5V Fig. 2 Adjustable Step-Down DC/DC Converter Si-Soft Research Center DS-2351G-03 20120302 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 AIC2351 ORDERING INFORMATION AIC2351-XXXXX XX PIN CONFIGURATION PACKING TYPE TR: TAPE & REEL BG: BAG FRONT VIEW 5 PACKAGE TYPE V5: SOT-23-5 4 GNxxG G: Green Package OUTPUT VOLTAGE DEFAULT: Adj. 12: 1.2V 15: 1.5V 18: 1.8V 25: 2.5V 33: 3.3V VIN VOUT 1 2 3 EN GND LX Fixed version FRONT VIEW VIN VFB 5 4 2351G 1 2 3 EN GND LX Adjustable version Example: AIC2351-33GV5TR 3.3V Output Version, in SOT-23-5 Green Package & Tape & Reel Packing Type AIC2351GV5TR Adjustable Version, in SOT-23-5 Green Package & Tape & Reel Packing Type Marking (Fixed Version) Part No. AIC2351-12GV5 AIC2351-15GV5 AIC2351-18GV5 AIC2351-25GV5 AIC2351-33GV5 Marking GN12G GN15G GN18G GN25G GN33G Marking (Adjustable Version) Part No. AIC2351GV5 Marking 2351G 2 AIC2351 ABSOLUTE MAXIMUM RATINGS VIN, LX to GND -0.3 V to 6.0V VFB, VOUT, EN to GND -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. 3 AIC2351 ELECTRICAL CHARACTERISTICS (TA=25C, VIN=3.6V, unless otherwise specified.) (Note 1) PARAMETER CONDITIONS SYMBOL MIN Input Voltage Range VIN 2.5 Output Adjustment Range Line Regulation Load Regulation VFB = VOUT, VIN = 3.6V, IOUT = 0A TA=25C AIC2351-12, IOUT = 0.1A AIC2351-15, IOUT = 0.1A AIC2351-18, IOUT = 0.1A AIC2351-25, IOUT = 0.1A AIC2351-33, IOUT = 0.1A Duty cycle = 100% to 23% IOUT = 0 to 600mA FB Input Current VFB = 1.4V Feedback Voltage Fixed Output Voltage VOUT VFB VFB 0.588 VOUT -2 -2 -2 -2 -2 TYP MAX UNITS 5.5 V VIN V 0.2 0.6 0.612 V +2 +2 +2 +2 +2 % % % % % 1 1.3 % % IFB 0.01 nA P-Channel On-Resistance ILX = 100mA, VIN=3.6V PRDS(ON) 0.4 0.65 N-Channel On-Resistance ILX = -100mA, VIN=3.6V NRDS(ON) 0.35 0.8 IPK 1.4 Peak Inductor Current Quiescent Current VFB=0.66V, IOUT=0A VFB=0.50V, IOUT=0A Shutdown Supply Current Oscillator Frequency Maximum Duty Cycle EN Pin Current VEN = VIN 100 fOSC DMAX IEN 1.2 100 A 30 50 A 150 0.1 1.5 220 1 1.8 0.1 1 A A MHz % A Output ON VENH 1.6 V Output OFF VENL 0.25 V 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). EN Input Threshold 4 AIC2351 TYPICAL PERFORMANCE CHARACTERISTICS 100 90 VOUT = 1.2V VOUT=1.8V 95 85 100mA 90 80 10mA 80 EFFICIENCY(%) EFFICIENCY(%) 85 600mA 75 70 65 1mA 60 VIN = 2.7V 75 70 VIN = 3.6V 65 VIN = 4.2V 60 55 50 55 50 2.5 3.0 3.5 4.0 4.5 5.0 45 5.5 1 10 INPUT VOLTAGE (V) Fig. 3 Efficiency vs. Input Voltage 100 VOUT = 1.8V VIN = 2.7V 85 VOUT = 2.5V 95 90 VIN = 2.7V VIN = 3.6V 90 85 80 EFFICIENCY(%) EFFICIENCY(%) 1000 Fig. 4 Efficiency vs. Output Current 95 75 VIN = 3.6V 70 VIN = 4.2V 65 75 70 65 60 55 55 50 1 10 100 1000 VIN = 3.6V VIN = 4.2V VIN = 4.2V 80 60 50 100 OUTPUT CURRENT (mA) VIN = 2.7V 1 10 100 1000 OUTPUT CURRENT (mA) OUTPUT CURRENT (mA) Fig. 5 Efficiency vs. Output Current Fig. 6 Efficiency vs. Output Current 100 VOUT = 3.3V 95 90 VIN = 5V EFFICIENCY(%) 85 80 75 70 65 60 55 50 1 10 100 1000 OUTPUT CURRENT(mA) Fig. 7 Efficiency vs. Output Current 5 AIC2351 TYPICAL PERFORMANCE CHARACTERISTICS (Continuous) VIN=5.5V, IOUT=600mA 3.390 OSCILLATOR FREQUENCY (Mhz) 1.6 OUTPUTE VOLTAGE (V) 3.385 3.380 3.375 3.370 3.365 3.360 -40 -20 0 20 40 60 VIN =4.2V 1.5 1.4 1.3 1.2 1.1 -40 80 -20 O 20 40 60 80 TEMPERATURE ( C) Fig. 8 Output Voltage vs. Temperature Fig. 9 Oscillator Frequency vs. Temperature 1.6 0.7 0.6 1.5 0.5 MAIN SWITCH 0.4 1.4 RDS(ON) OSCILLATOR FREQUENCY( Mhz) 0 O TEMPERATURE ( C) 0.3 SYNCHRONOUS SWITCH 0.2 1.3 0.1 1.2 2.5 3.0 3.5 4.0 4.5 5.0 0.0 2.5 5.5 3.0 INPUT VOLTAGE(V) 4.5 5.0 5.5 2.5 VOUT= 1.2V IOUT=0A Current Limit (A) 48 4.0 Fig. 11 RDS(ON) vs. Input Voltage 50 49 3.5 INPUT VOLTAGE (V) Fig. 10 Oscillator Frequency vs. Input Voltage 47 SUPPLY CURRENT (A) 46 45 44 43 42 41 40 39 VOUT=1.2V 2 1.5 1 0.5 0 38 2.5 37 3 3.5 4 4.5 5 5.5 36 35 3.0 3.5 4.0 4.5 5.0 5.5 Input Voltage (V) INPUT VOLTAGE (V) Fig. 12 Supply Current vs. Input Voltage Fig. 13 Current Limit vs. Input Voltage 6 AIC2351 TYPICAL PERFORMANCE CHARACTERISTICS (Continuous) Output Ripple Output Ripple ILX ILX IOUT IOUT VIN=3.6V; VOUT=1.2V; L=2.2F; COUT=10F; IOUT=0mA to 600mA Fig. 14 Load Transient Response VIN=3.6V; VOUT=1.2V; L=2.2F; COUT=10F; IOUT=200mA to 600mA Fig. 15 Load Transient Response Output Ripple Output Ripple ILX ILX IOUT IOUT VIN=3.6V; VOUT=1.8V; L=2.2F; COUT=10F; IOUT=50mA to 600mA Fig. 16 Load Transient Response Output Ripple VIN=3.6V; VOUT=1.8V; L=2.2F; COUT=10F; IOUT=100mA to 600mA Fig. 17 Load Transient Response VLX Output Ripple ILX IOUT VIN=3.6V; VOUT=1.8V; L=2.2F; COUT=10F; IOUT=200mA to 600mA Fig. 18 Load Transient Response ILX VIN=3.6V; VOUT=1.8V; L=2.2F; COUT=10F; IOUT=50mA Fig. 19 PFM Operation 7 AIC2351 BLOCK DIAGRAM PIN DESCRIPTIONS PIN 1: EN - ON/OFF Control Pin. The Device will turn off when EN is Low. This pin isn’t allowed to float. PIN 2: GND - Ground. PIN 3: LX - LX Pin. The LX node connects to the inductor. PIN 4: VIN - Main Power Supply Pin. PIN 5: VOUT - Output Voltage Feedback Pin. (For fixed version) PIN 5: VFB - Feedback Pin. (For adjustable version) 8 AIC2351 APPLICATION INFORMATION Operation frequency of AIC2351 will be reduced to third of the The AIC2351 is a low-noise and fixed-frequency step- normal switching frequency. This lower switching down DC/DC converter with current-mode PWM frequency ensures the inductor current has more time control internal to discharge, thereby preventing inductor current synchronous rectifier, which eliminates the external runaway. The switching frequency will automatically Schottky diode and increases efficiency. During normal return to its designed value while short circuit condition operation, the AIC2351 can regulate its output voltage is released. architecture. It features an through a feedback control circuit, which is composed of an error amplifier; a current comparator and several control signal generators. By comparing the feedback voltage to the reference voltage of 0.6V, the error Shutdown By connecting the EN pin to GND, the AIC2351 can be shut down to reduce the supply current to 0.1A amplifier varies its output voltage. The output voltage (typical). At this operation mode, the output voltage of of the error amplifier is compared with the summing step-down converter is equal to 0V. signal 100% Duty Cycle Operation of current sensing signal and slope compensation signal to determine the duty cycle of When the input voltage approaches the output voltage, internal main power switch (P-channel MOSFET). the AIC2351 smoothly transits to 100% duty cycle While the main power switch is turned on, the operation. This allows AIC2351 to regulate the output synchronous power switch (N-channel MOSFET) will voltage until AIC2351 completely enters 100% duty be turned off through anti-short-through block. Similarly, cycle operation. In 100% duty cycle mode, the output when the main power switch is turned off, the voltage is equal to the input voltage minus the voltage, synchronous power switch will be turned on until the which is the drop across the main power switch. inductor current starts to reverse or the beginning of The AIC2351 achieves 100% duty cycle operation by the next switching cycle. In order to achieve better extending the turn-on time of the main power switch. If efficiency output the summing signal of current sensing signal and slope pulse-frequency- compensation signal does not reach the output voltage modulated mode (PFM) operation while working at level of the error amplifier at the end of 90% switching light load conditions. period, the main power switch is continuously turned Current Limitation on and the oscillator remains off until the summing The AIC2351 provides current limit function by using signal an internal sensing resistor. When the main power compensation signal reaches the output voltage level switch turns on, current follows through the internal of the error amplifier. After the summing signal of sensing resistor. And current amplifier senses the current sensing signal and slope compensation signal voltage, which crosses the resistor, and amplifies it. reaches the output voltage level of the error amplifier, While the sensed voltage gets higher than reference the main power switch is turned off and the voltage, the current limitation function is activated. synchronous power switch is turned on for a constant While the current limitation function is activated, the off time. At the end of the constant off time, the next duty cycle will be reduced to limit the output power to switching cycle is begun. While the input voltage protect the internal power switches. approaches capacitor, and prevent AIC2351 will overcharging enter the Short Circuit Protection While the output is shorted to ground, the switching of current the sensing output signal voltage, and the slope switching frequency decreases gradually to smoothly transit to 100% duty cycle operation. 9 AIC2351 If input voltage is very close to output voltage, the For lower output voltage ripple, the use of low ESR switching mode goes from pure PWM mode to 100% ceramic capacitor is recommended. The tantalum duty cycle operation. During this transient state capacitor can also be used well, but its ESR is larger mentioned above, large output ripple voltage may than that of ceramic capacitor. appear on output terminal. When Components Selection 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 V 1 OUT V IN choosing the input and output ceramic because they retain their capacitance over wider ranges of voltage and temperature than other types. When using the ceramic capacitor as the input capacitor, the high input voltage transient may be generated at some start-up conditions, such as connecting the input to a live power source. By adding Accepting a large current ripple of inductor allows the a small resistor in series with the input ceramic use of a smaller inductance. However, higher current capacitor, the high input voltage transient can be ripple of inductor can cause higher output ripple improved. voltage and large core loss. By setting an acceptable Output Voltage Programming (AIC2351 Adjustable Version Only) By connecting a resistive divider R1 and R2, the output current ripple of inductor, a suitable inductance can be obtained from above equation. In addition, it is important to ensure the inductor saturation current exceeds the peak value of inductor voltage of AIC2351 step-down converter can be set. VOUT can be calculated as: peak value of inductor current can be calculated R VOUT 0.6 1 1 R2 according to the following equation. The resistive divider should sit as close to VFB pin as current in application to prevent core saturation. The IPEAK IOUT max possible. VOUT V 1 OUT 2 fOSC L VIN Layout Consideration 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 ) following points should be managed comprehensively. 1. The input capacitor and VIN should be placed as close as possible to each other to reduce the input voltage ripple and noise. 2. The output loop, which is consisted of the inductor, the internal main power switch, the internal synchronous power switch and the output capacitor, VOUT VIN VOUT 2 VIN IL2 12 The selection of output capacitor depends on the required output voltage ripple. The output voltage ripple can be expressed as: VOUT In order to ensure a proper operation of AIC2351, the IL ESR IL 8 fOSC COUT 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. 5. The VFB pin should be connected to the feedback resistors directly and the route should be away from the noise sources. 10 AIC2351 PHYSICAL DIMENSIONS SOT-23-5 (unit: mm) 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 θ L L1 A 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. 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. 11