ACE721G 5V 1A, 1.5MHz Synchronous Buck Converter Description The ACE721G Series is a high-efficiency, DC-to-DC step-down switching regulators, capable of delivering up to 1A of output current. The device operates from an input voltage range of 2.5V to 5.5V and provides an output voltage from 0.6V to VIN, making the ACE721G Series ideal for low voltage power conversions. Running at a fixed frequency of 1.5MHz allows the use of small external components, such as ceramic input and output caps, as well as small inductors, while still providing low output ripples. This low noise output along with its excellent efficiency achieved by the internal synchronous rectifier, making ACE721G Series an ideal green replacement for large power consuming linear regulators. Internal soft-start control circuitry reduces inrush current. Short-circuit and thermal-overload protection improves design reliability. The ACE721G Series is available in a SOT23-5 Package. Features • • • • • • • • • • High Efficiency: Up to 97% Capable of Delivering 1A 1.5MHz Switching Frequency No External Schottky Diode Needed Internal Compensation and Soft-Start Current Mode control 0.6V Reference for Low Output voltages Logic Control Shutdown (IQ<1uA) Thermal shutdown and UVLO Available in SOT23-5 Application • • • • • • • Cellular phones Digital Cameras MP3 and MP4 players Set top boxes Wireless and DSL Modems USB supplied Devices in Notebooks Portable Devices. VER 1.1 1 ACE721G 5V 1A, 1.5MHz Synchronous Buck Converter Absolute Maximum Rating Parameter Value Max Input Voltage 6V 125°C Max Operating Junction Temperature(Tj) Ambient Temperature(Ta) -40°C~+85°C Maximum Power Dissipation SOT-23-5 400mW Storage Temperature(Ts) -40°C~150°C Lead Temperature & Time 260°C 10S TAPE & REEL 3000/REEL Note1: Absolute Maximum Ratings are threshold limit values that must not be exceeded even for an instant under any condition. Moreover, such values for any two items must not be reached simultaneously. Operation above these absolute maximum ratings may cause degradation or permanent damage to the device. These are stress ratings only and do not necessarily imply functional operation below these limits. Typical Application Vin 2.5V to 5.5V IN 10uF SW Vout 1.8V/1A 2.2uH R1 240K FB GND 22uF R2 120K SYMBOL DESCRIPTTION Value Unit VIN VIN Supply Voltage 2.5 to 5.5 V TOPT Operating Temperature -40 to +85 C VER 1.1 2 ACE721G 5V 1A, 1.5MHz Synchronous Buck Converter Packaging Type SOT-23-5 Function SOT-23-5 Description 1 EN 2 GND 3 SW Inductor connection. Connect an inductor between SW and The regulator output 4 VIN Supply voltage 5 FB Feedback input. Connect and external resistor divider from the output to FB and GND to set the output to a voltage between 0.6V and Vin Enable pin for the IC. Drive the pin to high to enable the part and low to disable Ground Ordering information ACE721G XX + H Halogen - free Pb - free BN : SOT-23-5 SIMPLIFIED BLOCK DIAGRAM VER 1.1 3 ACE721G 5V 1A, 1.5MHz Synchronous Buck Converter Electrical Characteristics VDD=5, TA=25℃ Symbol VDD Vref Ifb Iq Parameter Conditions Input Voltage Range Feedback Voltage Feedback Leakage current Quiescent Current Min Typ Max Unit 5.5 V 0.6 0.615 V 0.1 0.4 uA 1 uA uA 2.5 0.585 Active, Vfb=0.65V, No Switching 70 Shutdown Fsoc Switching Frequency RdsonP PMOS Rdson 1.5 300 MHz mΩ RdsonN NMOS Rdson 150 mΩ Ilimit Peak Current Limit Iswlk SW Leakage Current Ienlk Vh_en EN Leakage Current EN Input High Voltage Vl_en EN Input Low Voltage 1.2 Vout=5.5V, VSW=0 or 5.5V, EN=0V A 10 uA 1 uA 0.4 V V 1.5 VER 1.1 4 ACE721G 5V 1A, 1.5MHz Synchronous Buck Converter Typical Characteristics (Typical values are at TA=25°C unless otherwise specified) VER 1.1 5 ACE721G 5V 1A, 1.5MHz Synchronous Buck Converter Typical Characteristics (Typical values are at TA=25°C unless otherwise specified) VER 1.1 6 ACE721G 5V 1A, 1.5MHz Synchronous Buck Converter DETAIL DESCRIPTION The ACE721G Series high-efficiency switching regulator is a small, simple, DC-to-DC step-down converter capable of delivering up to 1A of output current. The device operates in pulse-width modulation (PWM) at 1.5MHz from a 2.5V to 5.5V input voltage and provides an output voltage from 0.6V to VIN, making the ACE721G Series ideal for on-board post-regulation applications. An internal synchronous rectifier improves efficiency and eliminates the typical Schottky free-wheeling diode. Using the on resistance of the internal high-side MOSFET to sense switching currents eliminates current-sense resistors, further improving efficiency and cost. Loop Operation ACE721G Series uses a PWM current-mode control scheme. An open-loop comparator compares the integrated voltage-feedback signal against the sum of the amplified current-sense signal and the slope compensation ramp. At each rising edge of the internal clock, the internal high-side MOSFET turns on until the PWM comparator terminates the on cycle. During this on-time, current ramps up through the inductor, sourcing current to the output and storing energy in the inductor. The current mode feedback system regulates the peak inductor current as a function of the output voltage error signal. During the off cycle, the internal high-side P-channel MOSFET turns off, and the internal low-side N-channel MOSFET turns on. The inductor releases the stored energy as its current ramps down while still providing current to the output. Current Sense An internal current-sense amplifier senses the current through the high-side MOSFET during on time and produces a proportional current signal, which is used to sum with the slope compensation signal. The summed signal then is compared with the error amplifier output by the PWM comparator to terminate the on cycle. Current Limit There is a cycle-by-cycle current limit on the high-side MOSFET of 1.2A. When the current flowing out of SW exceeds this limit, the high-side MOSFET turns off and the synchronous rectifier turns on. ACE721G Series utilizes a frequency fold-back mode to prevent overheating during short-circuit output conditions. The device enters frequency fold-back mode when the FB voltage drops below 200mV, limiting the current to 1.2A and reducing power dissipation. Normal operation resumes upon removal of the short-circuit condition. VER 1.1 7 ACE721G 5V 1A, 1.5MHz Synchronous Buck Converter Soft-start ACE721G Series has a internal soft-start circuitry to reduce supply inrush current during startup conditions. When the device exits under-voltage lockout (UVLO), shutdown mode, or restarts following a thermal-overload event, the l soft-start circuitry slowly ramps up current available at SW. UVLO and Thermal Shutdown If IN drops below 2.5V, the UVLO circuit inhibits switching. Once IN rises above 2.5V, the UVLO clears, and the soft-start sequence activates. Thermal-overload protection limits total power dissipation in the device. When the junction temperature exceeds TJ= +160°C, a thermal sensor forces the device into shutdown, allowing the die to cool. The thermal sensor turns the device on again after the junction temperature cools by 15°C, resulting in a pulsed output during continuous overload conditions. Following a thermal-shutdown condition, the soft-start sequence begins. Design Procedure Setting Output Voltages Output voltages are set by external resistors. The FB_ threshold is 0.6V. RTOP = RBOT [(VOUT / 0.6) - 1] Input Capacitor Selection The input capacitor in a DC-to-DC converter reduces current peaks drawn from the battery or other input power source and reduces switching noise in the controller. The impedance of the input capacitor at the switching frequency should be less than that of the input source so high-frequency switching currents do not pass through the input source. The output capacitor keeps output ripple small and ensures control-loop stability. The output capacitor must also have low impedance at the switching frequency. Ceramic, polymer, and tantalum capacitors are suitable, with ceramic exhibiting the lowest ESR and high-frequency impedance. Output ripple with a ceramic output capacitor is approximately as follows: VRIPPLE = IL(PEAK)[1 / (2π x fOSC x COUT )] If the capacitor has significant ESR, the output ripple component due to capacitor ESR is as follows: VRIPPLE(ESR) = IL(PEAK) x ESR VER 1.1 8 ACE721G 5V 1A, 1.5MHz Synchronous Buck Converter Output Capacitor and Inductor Selection Follow the below table for Inductor and Output cap selection: VOUT 1.2V 1.5V 1.8V 2.5V COUT 33F 33F 22F 22F L 1.5H 3.3V 10F 1.5H 2.2H 3.3H 4.7H If much smaller values are used, inductor current rises, and a larger output capacitance may be required to suppress output ripple. Larger values than LIDEAL can be used to obtain higher output current, but typically with larger inductor size. Application Information Layout is critical to achieve clean and stable operation. The switching power stage requires particular attention. Follow these guidelines for good PC board layout: (1) Place decoupling capacitors as close to the IC as possible (2) Connect input and output capacitors to the same power ground node with a star ground configuration then to IC ground. (3) Keep the high-current paths as short and wide as possible. Keep the path of switching current (C1 to IN and C1 to GND) short. Avoid vias in the switching paths. (4) If possible, connect IN, SW, and GND separately to a large copper area to help cool the IC to further improve efficiency and long-term reliability. (5) Ensure all feedback connections are short and direct. Place the feedback resistors as close to the IC as possible. (6) Route high-speed switching nodes away from sensitive analog area. VER 1.1 9 ACE721G 5V 1A, 1.5MHz Synchronous Buck Converter Packing Information SOT-23-5 VER 1.1 10 ACE721G 5V 1A, 1.5MHz Synchronous Buck Converter Notes ACE does not assume any responsibility for use as critical components in life support devices or systems without the express written approval of the president and general counsel of ACE Electronics Co., LTD. As sued herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and shoes 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. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. ACE Technology Co., LTD. http://www.ace-ele.com/ VER 1.1 11