AIC2862 2A 23V Synchronous PWM/PSM Step-Down Converter with High Light-load Efficiency FEATURES DESCRIPTION 2A Continuous Output Current Wide 4.75V to 23V Operating Input Range Ouput Adjustable from 0.925V to 12V Up to 89% Efficiency for Heavy Load (Vin=12V, Vout=3.3V, Iout=2.0A) Up to 92% Efficiency for Moderate Load (Vin=12V, Vout=3.3V, Iout=1.0A) Up to 81% Efficiency for Light Load (Vin=12V, Vout=3.3V, Iout=20mA) Low Rds(on) Internal Switches: 140mΩ and 120mΩ <3µA Supply Current in Shutdown Mode 340KHz/550KHz Frequency Programmable Soft Start Thermal Shutdown Cycle by Cycle Over Current Protection Under Voltage Lockout Short Circuit Protection Over Voltage Protection APPLICATIONS Networking Systems such as Modems & Routers Distributed Power Systems Pre-Regulator for Linear Regulators Set-top Box The AIC2862 is a 2A synchronous-rectified Buck converter with integrated low Rds(on) power MOSFETs. The AIC2862, designed with a current-mode control scheme, can convert wide input voltage to the adjustable output voltage to provide excellent output voltage regulation. It is stable with low ESR output ceramic capacitors. For high efficiency over all load current range, the AIC2862 is equipped with an automatic PSM/PWM modeoperation. At light load, the IC operates in the PSM (Pulse Skipping Mode) to reduce switching losses. At heavy load, the IC works in PWM mode to provide high efficiency and excellent output voltage regulation. The AIC2862 is also equipped with softstart and whole protections (under-voltage, over-voltage, over-temperature, short circuit and current-limit) into a single package. This device, available in SOP-8 package, provides a very compact system solution with minimal external components and PCB area. TYPICAL APPLICATIONS CIRCUIT Typical Application Circuit Analog Integrations Corporation Si-Soft Research Center DS-2862G-02 20120807 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 AIC2862 PIN CONFIGURATION AIC2862-XXXX XX PIN CONFIGURATION PACKING TYPE TR: TAPE & REEL TB: TUBE SOP-8 Exposed Pad (Heat Sink) TOP VIEW PACKAGING TYPE R8: SOP-8 Exposed Pad (Heat Sink) G: GREEN PACKAGE BS 1 8 SS IN 2 7 EN SW 3 6 COMP GND 4 5 FB Note: The exposed pad must be connected with GND pin 3: fs=340KHz 5: fs=550KHz Example: AIC2862-3GR8TR 340KHz with GREEN SOP-8 Exposed Pad (Heat Sink) Package and TAPE & REEL Packing Type ABSOLUTE MAXIMUM RATINGS Input Voltage (VIN)…………………………………………………………………………………. - 0.3V to 26V SW Pin Voltage (Vsw) …………………………………………………………….………… -1V to VIN + 0.3V BS Pin Voltage ………………………………………………………………….………Vsw – 0.3V to Vsw + 6V EN Pin Voltage…………………………………………………………………………………….... - 0.3V to VIN All Other Pins Voltage……………………………………………………………………………..… - 0.3V to 6V Operating Ambient Temperature Range TA………...............................…….…..................... - 40C ~ 85C Operating Maximum Junction Temperature TJ……….……………...………….………………........... 150C Storage Temperature Range TSTG ......................................................................................... -65ºC~150ºC Lead Temperature (Soldering 10 Sec.)…………………………………………………..……………… 260C Thermal Resistance Junction to Case SOP-8 Exposed Pad*…………………………………..15C/W Thermal Resistance Junction to Ambient SOP-8 Exposed Pad*…………………………………..60C/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. 2 AIC2862 ELECTRICAL CHARACTERISTICS VIN=12V, unless otherwise specified. Typical values are at TA=+25C PARAMETER Supply Voltage Range Under Voltage Lockout Threshold UVLO Hysteresis Shutdown Supply Current Standby Current (Switching) Reference Voltage Feedback Over Voltage Threshold EN Shutdown Threshold Voltage EN Shutdown Hysteresis High-Side Switch On-Resistance Low-Side Switch On-Resistance High-Side Switch Leakage Current High-Side Switch Current Limit Oscillation Frequency fs=340KHz Oscillation Frequency fs=550KHz Short Circuit Oscillation Frequency Maximum Duty Cycle Minimum On Time Soft-Start Current Soft-Start Period Thermal Shutdown SYMBOL CONDITIONS VIN Rising VEN = 0V VEN = 3.0V; SW = NC VREF VFB Rising VEN Rising RDS(ON)1 RDS(ON)2 VEN = 0V, VSW = 0V Peak Current fs fs VFB = 0V DMAX TON VSS = 0V VSS = 0.1F Trip Point MIN 4.75 3.7 TYP 4.05 210 0.3 0.7 0.900 0.925 123 1.1 1.5 220 140 120 0 2.7 3.4 300 340 485 550 110 90 220 6 15 160 MAX UNITS 23 V V mV 3 A 1.5 mA 0.95 V % 2.2 V mV m m 10 A A 380 KHz 615 KHz KHz % ns A ms 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). 3 AIC2862 TYPICAL PERFORMANCE CHARACTERISTICS Fig. 1 Efficiency vs. Load Current at VIN = 12V Fig. 2 Start-Up Waveform at VOUT=3.3V, IOUT=2A Fig. 3 Start-Up Waveform at VOUT=3.3V, IOUT=2A Fig. 4 Shutdown Waveform at VOUT=3.3V, IOUT=2A Fig. 5 Shutdown Waveform at VOUT=3.3V, IOUT=2A Fig. 6 Load Transient at VOUT=3.3V, IOUT=1A to 2A 4 AIC2862 TYPICAL PERFORMANCE CHARACTERISTICS (Continued) Fig. 7 Load Transient at VOUT=3.3V, IOUT=0.5A to 2A Fig. 8 Stability Waveform at VOUT=3.3V, IOUT=1A Fig. 9 Stability Waveform at VOUT=3.3V, IOUT=2A 5 AIC2862 BLOCK DIAGRAM Functional Block Diagram of AIC2862 PIN DESCRIPTIONS Pin No. Pin Name 1 BS 2 IN 3 SW 4 5 GND FB 6 COMP 7 EN 8 SS Pin Function High Side Gate Drive Boost Input. BS supplies the drive for the high-side N-Channel MOSFET switch. Connect a 10nF or greater capaitor from SW to BS to power the high-side switch. Power Input. IN supplies power to the IC, as well as the step-down converter switches. By pass IN to GND with a suitabley large capacitor to eliminate noise on the input to the IC. Power Switching Output. SW is the switching node that supplies power to the output. Connect the output LC filter from switch to the output load. Note that a capacitor is required from SW to BS to power the high-side switch. Ground. Connect the exposed pad on backside to Pin 4. Feedback Input. FB senses the output voltage to regulate that voltage. Drive feedback with a resistive voltage divider from the output voltage. Compensation Node. COMP is used to compensate the regulation control loop. Connect a series RC network form COMP to GND to compensate the regulation control loop. In some cases, an additional capacitor from COMP to GND is required. Enable Input. EN is a digital input that turns the regulator on or off. Drive EN high to turn on the regulator. Drive it low to turn it off. For automatic strat-up, attach to IN with a 100k pull up resistor. Soft Star Contol Input. SS controls the soft star period. Connect a capacitor from SS to GND to set the soft-star period. To disable the soft-star feature, leave the SS pin unconnected. 6 AIC2862 APPLICATION INFORMATIONS The AIC2862 is a synchronous high voltage buck The AIC2862 provides the soft-start function. Initially, converter that can support the input voltage range from the voltage at SS pin is 0V. Then an internal current 4.75V to 23V and the output current can be up to 2A. source of 6A (typ.) charges an external soft-start capacitor. During the soft-start period, the voltage at SS Setting the Output Voltage pin will limit the feedback threshold voltage at FB pin. The output voltage is set using a resistive voltage When the voltage at SS pin is higher than 0.925V, the divider connected from the output voltage to FB. The feedback threshold voltage at FB pin reaches the de- voltage divider divides the output voltage down to the sired value. The soft-start time can be calculated in feedback voltage by the ratio: accordance with the following equation. VFB = VOUT t SS = C5 × R2 R1 + R2 The soft-start capacitor is discharged to GND when the Thus the output voltage is: VOUT = 0.925 × 0.925 V 6μA R1 + R2 R2 EN pin is connected to GND. Optional Schottky Diode A Schottky diode with low forward drop voltage and For example, for a 3.3V output voltage, R2 is 10kΩ, fast reverse recovery is the ideal choice for better and R1 is 26.1kΩ. efficiency. The forward drop voltage of a Schottky Inductor diode will result in the conduction losses in the diode, The inductor selection depends on the current ripple of inductor, the input voltage, and the output voltage. VOUT L fOSC IL VOUT 1 V IN and the diode capacitance (CT or CD) will cause the switching losses. Therefore, it is necessary to consider both forward voltage drop and diode capacitance for diode selection. In addition, the rating of selected Accepting a large current ripple of inductor allows the Schottky diode should be able to handle the input use of a smaller inductance. However, higher current voltage and the maximum peak diode current. ripple of inductor can cause higher output ripple Input Capacitor and Output Capacitor voltage and large core loss. By setting an acceptable current ripple of inductor, a suitable inductance can be obtained from above equation. 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 In addition, it is important to ensure the inductor is recommended. The approximated RMS current of saturation current exceeds the peak value of inductor the input capacitor can be calculated according to the current in application to prevent core saturation. The following equation. peak value of inductor current can be calculated according to the following equation. IPEAK IOUT max VOUT V 1 OUT 2 fOSC L VIN 2 ICINRMS IOUT (MAX ) VOUT VIN VOUT 2 VIN IL2 12 The selection of output capacitor depends on the required output voltage ripple. The output voltage Soft-Start ripple can be expressed as: 7 AIC2862 ΔVOUT = ΔIL 8 × f OSC × C3 + ESR The system may have another zero of importance, if ΔIL the output capacitor has a large capacitance and/or a 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 high ESR value. The zero, due to the ESR and capacitance of the output capacitor, is located at: FESR = than that of ceramic capacitor. When choosing the input and output ceramic 1 2π × C3 × RESR In this case, a third pole set by the compensation ca- capacitors, X5R and X7R types are recommended pacitor, C7 and the compensation resistor, Rc is used because they retain their capacitance over wider to compensate the effect of the ESR zero on the loop ranges of voltage and temperature than other types. gain. This pole is located at: Loop Compensation FP 2 = 1 2π × C7 × Rc ※ The values of the compensation components are given in the AIC2862 demo board user manual. Layout Consideration In order to ensure a proper operation of AIC2862, the In order to avoid the poor output voltage ripple and low following points should be managed comprehensively. efficiency caused by instability, AIC2862 requires a 1. The input capacitor and VIN should be placed as proper external compensation network to compensate close as possible to each other to reduce the input its feedback loop. In this external compensation voltage ripple and noise. network, the compensation resistor, RC, and the 2. The output loop, which is consisted of the inductor, compensation capacitor, CC, are used to set the high- the internal power switch, the Schottky diode and frequency integrator gain and the integrator zero. C7 is the output capacitor, should be kept as small as used to cancel the zero caused by the output capacitor possible. and it’s ESR. While using the ceramic capacitor as the output capacitor, C7 can be omitted due to the small and wide. 4. Logically the large current on the converter should ESR. The system has one pole of importance, due to the output capacitor, C3 and the load resistor. This poles is located at: FP1 = 3. The routes with large current should be kept short 1 2π × C3 × RLOAD The system has one zero of importance, due to the flow at the same direction. 5. In order to prevent the effect from noise, the IC’s GND pin should be placed close to the ground of the input bypass capacitor. 6. The FB pin should be connected to the feedback resistors directly and the route should be away from the noise sources. compensation capacitor, Cc and the compensation resistor, Rc. This zero is located at: FZ1 = 1 2π × Cc × Rc 8 AIC2862 PHYSICAL DIMENSIONS SOP-8 Exposed Pad(Heat Sink) D D1 EXPOSED THERMAL PAD(Heat Sink) (BOTTOM CENTER OF PACKAGE) h X 45° A SEE VIEW B A e A H E E1 WITH PLATING 0.25 C A1 B GAUGE PLANE SEATING PLANE L VIEW B BASE METAL SECTION A-A Note : 1. Refer to JEDEC MS-012E. 2. Dimension "D" does not include mold flash, protrusions or gate burrs. Mold flash, protrusion or gate burrs shall not exceed 6 mil per side . 3. Dimension "E" does not include inter-lead flash or protrusions. 4. Controlling dimension is millimeter, converted inch dimensions are not necessarily exact. S Y M B O L SOP-8 Exposed Pad(Heat Sink) MILLIMETERS MIN. MAX. A 1.35 1.75 A1 0.00 0.15 B 0.31 0.51 C 0.17 0.25 D 4.80 5.00 D1 1.50 3.50 E 3.80 4.00 E1 1.0 e 2.55 1.27 BSC H 5.80 6.20 h 0.25 0.50 L 0.40 1.27 θ 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. 9