AIC2863 3A 23V Synchronous PWM/PSM Step-Down Converter with High Light-load Efficiency FEATURES DESCRIPTION 3A Continuous Output Current Wide 4.75V to 23V Operating Input Range Ouput Adjustable from 0.925V to 12V (VREF=0.925V Version) Ouput Adjustable from 0.8V to 12V (VREF=0.8V Version) Up to 84% Efficiency for Heavy Load (Vin=12V, Vout=3.3V, Iout=3.0A) Up to 91% Efficiency for Moderate Load (Vin=12V, Vout=3.3V, Iout=1.0A) Low Rds(on) Internal Switches: 100mΩ and 85mΩ <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 The AIC2863 is a 3A synchronous-rectified Buck converter with integrated low Rds(on) power MOSFETs. The AIC2863, designed with a currentmode 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 AIC2863 is equipped with an automatic PSM/PWM mode operation. 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 AIC2863 is also equipped with soft start 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. APPLICATIONS Networking Systems such as Modems & Routers Distributed Power Systems Pre-Regulator for Linear Regulators Set-top Box TYPICAL APPLICATIONS CIRCUIT AIC2863 Typical Application Circuit Analog Integrations Corporation Si-Soft Research Center DS-2863G-04 20121218 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 AIC2863 PIN CONFIGURATION AIC2863-XXXXX XX PIN CONFIGURATION PACKING TYPE TR: TAPE & REEL TB: TUBE PACKAGING TYPE R8: SOP-8 Exposed Pad (Heat Sink) G: GREEN PACKAGE SOP-8 Exposed Pad (Heat Sink) TOP VIEW 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 Default: VREF=0.925V K: V REF =0.8V Example: AIC2863-3GR8TR VREF =0.925V, fs=340KHz with GREEN SOP-8 Exposed Pad (Heat Sink) Package and TAPE & REEL Packing Type AIC2863-K5GR8TR VREF =0.8V, fs=550KHz 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 toVSW+6V EN Pin Voltage ...................................................................................................................... -0.3V to VIN All Other Pins Voltage ........................................................................................................... -0.3V to 6V Operating Ambient Temperature Range TA ......................................................................... -40ºC~85ºC Operating Maximum Junction Temperature TJ ............................................................................. 150ºC Storage Temperature Range TSTG ..................................................................................... -65ºC~150ºC Lead Temperature (Soldering 10 Sec.) ........................................................................................ 260ºC 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 AIC2863 ELECTRICAL CHARACTERISTICS (VIN=12V, VEN =5V, TA=25C, unless otherwise specified.) (Note1) PARAMETER Supply Voltage Range Under Voltage Lockout Threshold UVLO Hysteresis Shutdown Supply Current SYMBOL VIN Rising MIN 4.75 3.7 VEN = 0V IOUT = 0A, VFB = 1.0V No Switching Standby Current Reference Voltage (Default Version) (Note2) Reference Voltage (K Version) (Note2) 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 (3 Version) (Note2) Oscillation Frequency (5 Version) (Note2) Short Circuit Oscillation Frequency Maximum Duty Cycle Minimum On Time Soft-Start Current Soft-Start Period Thermal Shutdown CONDITIONS TYP 4.05 210 0.3 MAX UNITS 23 V 4.5 V mV 3 A 0.7 1.5 mA VREF 0.90 0.925 0.95 V VREF 0.778 0.8 0.822 V VFB Rising VEN Rising 1.1 VEN = 0V, VSW = 0V Peak Current 4.0 123 1.5 220 100 85 0 5.8 fs 300 340 380 KHz fs 485 550 615 KHz RDS(ON)1 RDS(ON)2 VFB = 0V DMAX TON VSS = 0V VSS = 0.1F Trip Point 110 90 220 6 15 160 2.2 10 % V mV m m A A 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). Note 2: Referring to the ordering information. 3 AIC2863 TYPICAL PERFORMANCE CHARACTERISTICS VIN 10V/Div VOUT 2V/Div VSW 10V/Div IL 2A/Div VIN=12V,VOUT=3.3V,IOUT=3A Time(20ms/Div) Fig. 1 Efficiency vs. Load Current VIN 5V/Div Fig. 2 Start-Up Waveform at VOUT=3.3V, IOUT=3A VIN 5V/Div VOUT 2V/Div VOUT 2V/Div VSW 10V/Div VSW 10V/Div IL 5A/Div VIN=12V,VOUT=3.3V,IOUT=3A IL 5A/Div VIN=12V,VOUT=3.3V,IOUT=3A Time(4ms/Div) Time(4ms/Div) Fig. 3 Start-Up Waveform at VOUT=3.3V, IOUT=3A Fig. 4 Shutdown Waveform at VOUT=3.3V, IOUT=3A VIN=12V,VOUT=3.3V,IOUT=0.5A~2.5A VOUT AC 500mV/Div VIN=12V,VOUT=3.3V,IOUT=1A~3A VOUT AC 500mV/Div IL 2A/Div IL 2A/Div Time(1ms/Div) Fig. 5 Load Transient at VOUT=3.3V, IOUT=0.5A to 2.5A Time(1ms/Div) Fig. 6 Load Transient at VOUT=3.3V, IOUT=1A to 3A 4 AIC2863 TYPICAL PERFORMANCE CHARACTERISTICS (Continued) VOUT AC 20mV/Div VOUT AC 20mV/Div VSW 5V/Div VSW 5V/Div IL 1A/Div IL 2A/Div VIN=12V,VOUT=3.3V,IOUT=1A Time(2μs/Div) Fig. 7 Stability Waveform at VOUT=3.3V, IOUT=1A VIN=12V,VOUT=3.3V,IOUT=3A Time(2μs/Div) Fig. 8 Stability Waveform at VOUT=3.3V, IOUT=3A 5 AIC2863 BLOCK DIAGRAM Functional Block Diagram of AIC2863 (VREF=0.925V Version) Functional Block Diagram of AIC2863 (VREF=0.8V Version) 6 AIC2863 PIN DESCRIPTIONS Pin 1: BS: High Side Gate Drive Boost Input. BS supplies the drive for the highside N-Channel MOSFET switch. Connect a 100nF or greater capaitor from SW to BS to power the high-side switch. Pin 2: IN: Power Input. IN supplies the power to the IC, as well as the stepdown converter switches. Drive IN with a 4.5V to 23V power source. By pass IN to GND with a suitably large capacitor to eliminate noise on the input to the IC. Pin 3: SW: 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. Pin 4:GND: Ground. Connect the exposed pad on backside to Pin 4. Pin 5: FB: Feedback Input. FB senses the output voltage to regulate that voltage. Drive feedback with a resistive voltage divider from the output voltage. Pin 6: COMP: 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. Pin 7: EN: 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. Pin 8: SS: Soft Star Control Input. SS controls the soft star period. Connect a capacitor from SS to GND to set the soft-star period. A 0.1F capacitor sets the soft-star period to 15ms. 7 AIC2863 APPLICATION INFORMATIONS Soft-Start The AIC2863 provides the soft-start function. Initially, The AIC2863 is a synchronous high voltage buck the voltage at SS pin is 0V. Then an internal current converter that can support the input voltage range from source of 6A (typ.) charges an external soft-start ca- 4.75V to 23V and the output current can be up to 3A. pacitor. During the soft-start period, the voltage at SS pin will limit the feedback threshold voltage at FB pin. Setting the Output Voltage When the voltage at SS pin is higher than reference The output voltage is set using a resistive voltage voltage, the feedback threshold voltage at FB pin divider connected from the output voltage to FB. The reaches the desired value. The soft-start time can be voltage divider divides the output voltage down to the calculated in accordance with the following equation. feedback voltage by the ratio: VFB = VOUT t SS C5 R2 R1 + R2 VREF 6A The soft-start capacitor is discharged to GND when the EN pin is connected to GND. Thus the output voltage is: VOUT R1 R2 VREF R2 For example, for Optional Schottky Diode A Schottky diode with low forward drop voltage and a 3.3V output voltage and VREF=0.925V, R2 is 10kΩ, and R1 is 25.6kΩ. fast reverse recovery is the ideal choice for better efficiency. The forward drop voltage of a Schottky diode will result in the conduction losses in the diode, Inductor and the diode capacitance (CT or CD) will cause the The inductor selection depends on the current ripple of switching losses. Therefore, it is necessary to consider inductor, the input voltage and the output voltage. both forward voltage drop and diode capacitance for L VOUT fOSC IL V 1 OUT VIN Accepting a large current ripple of inductor allows the diode selection. In addition, the rating of selected Schottky diode should be able to handle the input voltage and the maximum peak diode current. use of a smaller inductance. However, higher current ripple of inductor can cause higher output ripple Input Capacitor and Output Capacitor voltage and large core loss. By setting an acceptable To prevent the high input voltage ripple and noise current ripple of inductor, a suitable inductance can be resulted from high frequency switching, the use of low obtained from above equation. ESR ceramic capacitor for the maximum RMS current In addition, it is important to ensure the inductor saturation current exceeds the peak value of inductor current in application to prevent core saturation. The peak value of inductor current can be calculated according to the following equation. IPEAK IOUT max VOUT V 1 OUT 2 fOSC L VIN is recommended. The approximated RMS current of the input capacitor can be calculated according to the following equation. 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 ripple can be expressed as: 8 AIC2863 ΔVOUT = 8 × f OSC ΔI L + ESR × (C3 // C4) ΔI L FZ1 = 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 choosing the input The system may have another zero of importance, if the output capacitor has a large capacitance and/or a high ESR value. The zero, due to the ESR and capacitance of the output capacitor, is located at: than that of ceramic capacitor. When 1 2π × Cc × Rc and output ceramic FESR = capacitors, X5R and X7R types are recommended 1 2π × (C3 // C4) × RESR because they retain their capacitance over wider In this case, a third pole set by the compensation ca- ranges of voltage and temperature than other types. pacitor, C7 and the compensation resistor, Rc is used to compensate the effect of the ESR zero on the loop Loop Compensation gain. This pole is located at: FP 2 = 1 2π × C7 × Rc ※ The values of the compensation components are given in the AIC2863 demo board user manual. Layout Consideration In order to avoid the poor output voltage ripple and low efficiency caused by instability, AIC2863 requires a proper external compensation network to compensate its feedback loop. In this external compensation network, the compensation resistor, RC, and the compensation capacitor, CC, are used to set the highfrequency integrator gain and the integrator zero. C7 is used to cancel the zero caused by the output capacitor and it’s ESR. While using the ceramic capacitor as the output capacitor, C7 can be omitted due to the small ESR. The system has one pole of importance, due to the output capacitor, C3//C4 and the load resistor. This poles is located at: 1 FP1 = 2π × (C3 // C4) × RLOAD The system has one zero of importance, due to the compensation capacitor, Cc and the compensation resistor, Rc. This zero is located at: In order to ensure a proper operation of AIC2863, the 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 power switch, the Schottky diode 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. 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. 9 AIC2863 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 2.55 e 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. 10