ACE721E 1A, 1.5MHz Step-Down Converter Description The ACE721E is a high-efficiency, DC-to-DC step-down switching regulator, capable of delivering up to 1A of output current. The devices operate from an input voltage range of 2.6V to 5.5V and provide output voltages from 0.6V to VIN, making the ACE721E ideal for low voltage power conversions. Running at a fixed frequency of 1.5MHz allows the use of small inductance value and low DCR inductors, thereby achieving higher efficiencies. Other external components, such as ceramic input and output caps, can also be small due to higher switching frequency, while maintaining exceptional low noise output voltages. Built-in EMI reduction circuitry makes this converter ideal power supply for RF applications. Internal soft-start control circuitry reduces inrush current. Short-circuit and thermal-overload protection improves design reliability. Features • • • • • • Up to 96% Efficiency Up to 1A Max Output Current 1.5MHz Frequency Light Load operation Internal Compensation and Soft-Start Tiny SOT-23-5 DFN2x2-6 Package Application • • • • • • MIDs, Tablet PC Set Top Boxes USB ports/Hubs Hot Swaps Cellphones Blue tooth. Absolute Maximum Rating Parameter Value IN, SW, FB, EN Voltage -0.3V~6.5V SW to ground current Internally limited Maximum Power Dissipation 400mW Operating Temperature Range -40°C~85°C Storage Temperature Range -55°C~150°C SOT23-5 400mW DFN2x2x6L 606mW Thermal Resistance Note: Exceed these limits to damage to the device. Exposure to absolute maximum rating conditions may affect device reliability. VER 1.3 1 ACE721E 1A, 1.5MHz Step-Down Converter Typical Application Efficiency Vs IOUT 1.8V/1A 1.5MHz Step-Down Converter Packaging Type SOT-23-5 DFN2*2-6L SOT-23-5 DFN2*2-6 Description 1 2 EN 2 1/5/7 GND 3 4 SW 4 3 IN 5 6 FB Function Enable pin for the IC. Drive this pin high to enable the part, low to disable. Ground Inductor Connection. Connect an inductor Between SW and the regulator output. Supply Voltage. Bypass with a 10μF ceramic capacitor to GND Feedback Input. Connect an external resistor divider from the output to FB and GND to set the output to a voltage between 0.6V and VIN Ordering information ACE721E XX + H Halogen - free Pb - free BN : SOT-23-5 MN: DFN2*2-6 VER 1.3 2 ACE721E 1A, 1.5MHz Step-Down Converter Block Diagram Electrical Characteristics VIN=VEN=5, TA=25℃ Parameter Input Voltage Range Conditions Min Typ Max Unit 6 V 2.31 2.45 V 40 70 uA 1 uA 0.612 V 2.6 Input UVLO Rising, Hysteresis=90mV Input Supply Current VFB =0.65V 2.31 Input Shutdown Current FB Feedback Voltage VIN =2.5 to 5V 0.588 FB Input Current 0.6 0.01 Output Voltage Range 0.6 uA Load Regulation VOUT =1.8V, IOUT From 0.2A to 0.4A 0.1 V % Line Regulation VIN =2.7 to 5.5V 0.2 %V 1.5 MHz Switching Frequency VIN NMOS Switch On Resistance ISW =200mA 200 mΩ PMOS Switch On Resistance ISW =200mA 280 mΩ PMOS Switch Current Limit SW Leakage Current 1.5 VIN=5.5V,VSW=0 or 5.5V,EN= GND EN Input Current EN Input Low Voltage EN Input High Voltage A 10 uA 1 uA 0.4 V 1.5 VER 1.3 V 3 ACE721E 1A, 1.5MHz Step-Down Converter Typical Characteristics (Typical values are at TA=25°C unless otherwise specified) Efficiency Vs IOUT IOUT (A) Efficiency Vs IOUT IOUT (A) Efficiency Vs IOUT IOUT (A) Load Transient Response VOUT VS IOUT IOUT(mA) VOUT Vs VIN VIN=3.6V,VOUT=1.2V,IOUT=0.2A to 1A VIN(V) Load Transient Response Load Transient Response Heavy Load Switching Waveform VIN=3.6V, VOUT=1.8V, IOUT=0.2A to 1A VIN=5V, VOUT=3.3V, IOUT=0.5A to 1A VIN=3.6V, VOUT=1.8V, IOUT=0.5A VER 1.3 4 ACE721E 1A, 1.5MHz Step-Down Converter Typical Characteristics (Typical values are at TA=25°C unless otherwise specified) Startup Waveform with EN Turn on Startup Waveform with EN Tied to IN Startup Waveform with EN Turn on VIN=5V, VOUT=3.3V Into 1A Resistive VIN=5V, VOUT=3.3V Into 1A Resistive VIN=5V, VOUT=3.3V 1A Resistive Load Startup Waveform with EN Tied to IN Short Circuit Response Short Circuit Recovery VIN=5V, VOUT=1.8V Into NoLoad VIN=5V, VOUT=3.3V VIN=5V,VOUT=3.3V VER 1.3 5 ACE721E 1A, 1.5MHz Step-Down Converter FUNCTION DESCRIPTION The ACE721E 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 2.6V to 5.5V input voltage and provides an output voltage from 0.6V to VIN, making the ACE721E 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 ACE721E 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. When the current flowing out of SW exceeds this limit, the high-side MOSFET turns off and the synchronous rectifier turns on. ACE721E 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 IPEAK and reducing power dissipation. Normal operation resumes upon removal of the short-circuit condition. Soft-start ACE721E has an 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. VER 1.3 6 ACE721E 1A, 1.5MHz Step-Down Converter UVLO and Thermal Shutdown If IN drops below 2.4V, the UVLO circuit inhibits switching. Once IN rises above 2.6V, 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 = RBOTTOM x [(VOUT / 0.6) - 1] Input Capacitor and Output 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. Input ripple with a ceramic capacitor is approximately as follows: VRIPPLE = IL(PEAK)[1 / (2π x fOSC x CIN)] If the capacitor has significant ESR, the output ripple component due to capacitor ESR is as follows: VRIPPLE(ESR) = IL(PEAK) x ESR 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. Inductor Selection A reasonable inductor value (LIDEAL) can be derived from the following: LIDEAL = [2(VIN) x D(1 - D)] / IOUT x fOSC PCB LAYOUT GUIDE PCB layout is very important to achieve stable operation. It is highly recommended to duplicate EVB layout for optimum performance. If change is necessary, please follow these guidelines and take Figure for reference. 1) Keep the path of switching current short and minimize the loop area formed by input cap, high-side MOSFET and low-side MOSFET. 2) Bypass ceramic capacitors are suggested to be put close to the Vin pin. 3) Ensure all feedback connections are short and direct. Place the feedback resistors and compensation components as close to the chip as possible. 4) Rout SW away from sensitive analog areas such as FB. 5) Connect IN, SW, and especially GND respectively to a large copper area to cool the chip to improve thermal performance and long-term reliability. VER 1.3 7 ACE721E 1A, 1.5MHz Step-Down Converter Packing Information SOT-23-5 VER 1.3 8 ACE721E 1A, 1.5MHz Step-Down Converter Packing Information DFN2x2-6L VER 1.3 9 ACE721E 1A, 1.5MHz Step-Down 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 1.3 10