AIC2359 1A Dual Synchronous Step-down DC/DC Converter FEATURES DESCRIPTION The AIC2359 is a dual output, low-noise, pulse-width-modulated (PWM), DC-DC stepdown converter. It powers logic and transmitters in small wireless systems such as cellular phones, communicating PDAs, and handyterminals. 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 AIC2359 is ideally suited for LiIon 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 AIC2359 include high efficiency, soft start, over temperature protection, and over current protection. It is available in a space-saving 12-pin DFN. Dual 1A Output 2.5V to 5.5V Input Range Accurate Reference 0.6V Provides Low Output Voltages Adjustable Output Voltage Up to 95% Efficiency Stable with Low ESR Output Ceramic Capacitors No Schottky Diode Required. 65µA Quiescent Current per Channel. 100% Duty Cycle in Low Dropout Operation. 1.5MHz Fixed-Frequency PWM Operation APPLICATIONS Digital Still Cameras Cellular Phones Wireless and DSL Modems Notebook Chipset Supplies. PDAs and Handy-Terminals. Battery-Operated Devices (1 Li-Ion or 3 NiMH/ NiCd). TYPICAL APPLICATIONS CIRCUIT 2.2uH Vout2 L2 10uF Cout2 R21 1 Vin2 4.7uF Cin2 2 3 4 R12 5 22pF R11 C11 6 VIN2 EN2 LX2 NC2 GND FB2 FB1 GND NC1 LX1 EN1 VIN1 12 11 22pF C21 R22 10 9 8 4.7uH Cin1 7 Vin1 AIC2359 2.2uH Vout1 L1 10uF Cout1 Fig. 1 Adjustable Output Voltage Step-Down DC/DC Converter Analog Integrations Corporation Si-Soft Research Center DS-2359G-02 20120209 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 AIC2359 Fig. 2 Fixed Output Voltage Step-Down DC/DC Converter 2 AIC2359 ORDERING INFORMATION PIN CO NFIGURATI ON A IC235 9-XX XX X XX P ACK ING TYP E TR: TA PE & REE L B G: BA G P ACK AGE TYP E DF: DFN-12 wit h he at sin k (3 x3 x0. 75-0.4 5mm ) G: Green Package Outpu t V olta ge: Vou t1/V out2 Def ault Ad justa ble -ZK:3 .3V /1.8V -ZE:3 .3V /1.2V -RK: 2.5V /1.8 V D FN-12 with heat s ink T OP VIEW VIN 2 1 12 EN 2 LX2 2 11 N C2 G ND 3 10 FB2 FB1 4 9 GN D N C1 5 8 LX1 EN 1 6 7 VIN1 Note : The expo sed pa d m ust be co nn ecte d with GND pin. E xa mple: A IC23 59GDFTR in Gree n P acka ge DFN-12 W ith Heat Sink Package and Tape & R eel Packin g Type A IC23 59-ZKGDFTR 3.3V /1.8 V V out Ve rsio n in Green Package DFN-12 W ith Hea t S ink P acka ge an d Ta pe & Ree l P acking T ype ABSOLUTE MAXIMUM RATINS Supply Input Volatge, VIN1, VIN2 6.0V -0.3V to VIN Pin Voltage for all other Pins -40C to 85C Operating Ambient Temperature Range TA Operating Maximum Junction Temperature TJ 150C -65C to 150C Storage Temperature Range TSTG 260C Lead Temperature (Soldering 10 Sec.) Thermal Resistance Junction to Case DFN-12L (3x3)* 20C/W Thermal Resistance Junction to Ambient DFN-12L (3x3)* 50C/W (Assume no Ambient Airflow) Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. *The package is place on a two layers PCB with 2 ounces copper and 2 square inch, connected by 8 vias. 3 AIC2359 ELECTRICAL CHARACTERISTICS (VIN=3.6V, VOUT=2.5V, unless otherwise specified. Typical values are at TA=25C) PARAMETER Input Voltage Range Reference Voltage SYMBOL CONDITIONS VIN 2.2 VREF 0.588 FB Input Current IFB VFB = 0.62V Quiesecnt Current IQ IOUT = 0mA, VFB = VREF + 5% Shutdown Supply Current ISHDN Enable High Input Voltage VEN_H Enable Low Input Voltage VEN_L Output Adjustment Range VOUT Output Voltage Accuracy MIN TYP MAX UNITS 5.5 V 0.612 V 50 nA 65 85 uA 0.1 1 uA VIN V 0.4 V VIN - ΔV V VOUT 3 % 0.6 -50 1.5 (ΔV = IOUT x PRDS(ON)) ΔVOUT VREF -3 P-Channel On-Resistance PRDS(ON) IOUT=200mA 0.28 0.39 N-Channel On-Resistance NRDS(ON) IOUT=200mA 0.25 0.39 P-Channel Current-Limit Threshold Oscillator Frequency fOSC Maximum Duty Cycle dutyMAX Thermal Shutdown Temperature TSD LX Leakage Current ILX IOUT=100mA 1.3 1.6 1.2 1.5 A 1.8 100 % 150 VLX=0V or VLX=3.6V -1 MHz °C 1 uA 4 AIC2359 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 5 AIC2359 TYPICAL PERFORMANCE CHARACTERISTICS (Continuous) Fig. 9 Oscillator Frequency vs. Input Voltage Fig. 11 Supply Current vs. Input Voltage Fig. 13 Load Transient Response Fig. 10 RDS(ON) vs. Input Voltage Fig. 12 Current Limit vs. Input Voltage Fig. 14 Load Transient Response 6 AIC2359 TYPICAL PERFORMANCE CHARACTERISTICS (Continuous) Fig. 15 Load Transient Response Fig. 16 Load Transient Response Fig. 17 Load Transient Response Fig. 18 PSM Operation 7 AIC2359 BLOCK DIAGRAM PIN DESCRIPTIONS Pin Number Pin Name Pin Function 1 VIN2 Power Input of Channel 2. 2 LX2 Pin for Switching of Channel 2. 3, 9, Exposed Pad (13) GND Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. 4 FB1 Feedback of Channel 1. 5, 11 NC1, NC2 6 EN1 Chip Enable of Channel 1 (Active High). VEN1 ≦ VIN1. 7 VIN1 Power Input of Channel 1. 8 LX1 Pin for Switching of Channel 1. 10 FB2 Feedback of Channel 2. 12 EN2 Chip Enable of Channel 2 (Active High). VEN2 ≦ VIN2. No Connection or Connect to VIN. 8 AIC2359 APPLICATION INFORMATION Operation frequency of AIC2359 will be reduced to one third of the The AIC2359 is a low-noise step-down DC/DC converter normal with current-mode PWM/PSM control architecture. It frequency ensures the inductor current has more time to features which discharge, thereby preventing inductor current runaway. eliminates the external Schottky diode and increases The switching frequency will automatically return to its efficiency. During normal operation, the AIC2359 can designed value while short circuit condition is released. an internal synchronous rectifier, switching frequency. This lower switching regulate its output voltage 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 amplifier varies its output voltage. The output voltage of the error amplifier is compared with the Shutdown By connecting the EN pin to GND, the AIC2359 can be shut down to reduce the supply current to 0.1 A (typical). At this operation mode, the output voltage of step-down converter is equal to 0V. summing signal of current sensing signal and slope 100% Duty Cycle Operation compensation signal to determine the duty cycle of When the input voltage approaches the output voltage, internal main power switch (P-channel MOSFET). While the AIC2359 smoothly transits to 100% duty cycle the main power switch is turned on, the synchronous operation. This allows AIC2359 to regulate the output power switch (N-channel MOSFET) will be turned off voltage until AIC2359 completely enters 100% duty cycle through anti-short-through block. Similarly, when the main operation. In 100% duty cycle mode, the output voltage is power switch is turned off, the synchronous power switch equal to the input voltage minus the voltage, which is the will be turned on until the inductor current starts to reverse drop across the main power switch. or the beginning of the next switching cycle. In order to achieve better efficiency and prevent overcharging the output capacitor, AIC2359 will enter pulse-skippingmodulated mode (PSM) operation while working at light load conditions. The AIC2359 achieves 100% duty cycle operation by extending the turn-on time of the main power switch. If the summing signal of current sensing signal and slope compensation signal does not reach the output voltage level of the error amplifier at the end of 90% switching period, the Current Limitation main power switch is continuously turned on and the oscilla- The AIC2359 provides current limit function by using an in- tor remains off until the summing signal of current sensing ternal sensing resistor. When the main power switch turns signal and slope compensation signal reaches the output on, current follows through the internal sensing resistor. And voltage level of the error amplifier. After the summing signal current amplifier senses the voltage, which crosses the re- of current sensing signal and slope compensation signal sistor, and amplifies it. While the sensed voltage gets higher reaches the output voltage level of the error amplifier, than reference voltage, the current limitation function is acti- the main power switch is turned off and the synchronous vated. While the current limitation function is activated, the power switch is turned on for a constant off time. At the end duty cycle will be reduced to limit the output power to protect of the constant off time, the next switching cycle is begun. the internal power switches. While the input voltage approaches the output voltage, the Short Circuit Protection switching frequency decreases gradually to smoothly transit While the output is shorted to ground, the switching to 100% duty cycle operation. 9 AIC2359 If input voltage is very close to output voltage, the switching mode goes from pure PWM mode to 100% duty cycle operation. During this transient state mentioned above, large output ripple voltage may appear on output terminal. VOUT IL ESR IL 8 fOSC COUT For lower output voltage ripple, the use of low ESR ceramic capacitor is recommended. The tantalum capacitor can also be used well, but its ERS is larger than that of ceramic capacitor. Components Selection When choosing the input and output ceramic capacitors, Inductor The inductor selection depends on the current ripple of inductor, the input voltage and the output voltage. VOUT L fOSC IL X5R and X7R types are recommended because they retain their capacitance over wider ranges of voltage and temperature than other types. V 1 OUT VIN Accepting a large current ripple of inductor allows the use Output Voltage Programming (AIC2359 Adjustable Version Only) By connecting a resistive divider R11 and R12 (R21 and R22), of a smaller inductance. However, higher current ripple of the output voltage of AIC2359 step-down converter can inductor can cause higher output ripple voltage and large be set. VOUT1 and VOUT2 can be calculated as: core loss. By setting an acceptable current ripple of R VOUT 1 0.6 1 11 R12 inductor, a suitable inductance can be obtained from above equation. current exceeds the peak value of inductor current in R VOUT 2 0.6 1 21 R22 application to prevent core saturation. The peak value of The resistive divider should sit as close to VFB pin as inductor current can be calculated according to the possible. following equation. Layout Consideration In addition, it is important to ensure the inductor saturation IPEAK IOUT max VOUT V 1 OUT 2 fOSC L VIN In order to ensure a proper operation of AIC2359, the following points should be managed comprehensively. 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 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, should VOUT VIN VOUT 2 VIN 3. The routes with large current should be kept short and IL2 12 The selection of output capacitor depends on the required output voltage ripple. The output voltage ripple can be expressed as: as possible to each other to reduce the input voltage be kept as small as possible. following equation. 2 ICINRMS IOUT (MAX ) 1. The input capacitor and VIN should be placed as close 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 AIC2359 PHYSICAL DIMENSIONS (unit: mm) DFN 12L-3x3x0.75-0.45mm PACKAGE OUTLINE DRAWING D2 D 12 E E2 L 7 6 A A3 1 e PIN#1 S Y M B O L DFN 12L-3x3x0.75-0.45mm MILLIMETERS MIN. MAX. 0.70 0.80 A A3 b SEATING PLANE 0.20 BSC b 0.18 0.30 D 2.90 3.10 D2 2.20 2.70 E 2.90 3.10 E2 1.40 1.80 0.45 BSC e L 0.30 0.50 Note : 1. DIMENSION AND TOLERANCING CONFORM TO ASME Y14.5M-1994. 2.CONTROLLING DIMENSIONS：MILLIMETER，CONVERTED INCH DIMENSION ARE NOT NECESSARILY EXACT. 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