ACE727C 600KHz, 16V, 2A Synchronous Step-Down Converter Description The ACE727C is a fully integrated, high– efficiency 2A synchronous rectified step-down converter. The ACE727C operates at high efficiency over a wide output current load range. This device offers two operation modes, PWM control and PFM Mode switching control, which allows a high efficiency over the wider range of the load. The ACE727C requires a minimum number of readily available standard external components and is available in a 6-pin SOT23 ROHS compliant package. Features • • • • • • • • • • • • • • High Efficiency: Up to 96% 600KHz Frequency Operation 2A Output Current No Schottky Diode Required 3.5V to 18V Input Voltage Range 0.6V Reference Slope Compensated Current Mode Control for Excellent Line and Load Transient Response Integrated internal compensation Stable with Low ESR Ceramic Output Capacitors Over Current Protection with Hiccup-Mode Thermal Shutdown Inrush Current Limit and Soft Start Available in SOT23-6 -40°C to +85°C Temperature Range Application • • • • • Distributed Power Systems Digital Set Top Boxes Flat Panel Television and Monitors Wireless and DSL Modems Notebook Computer Absolute Maximum Ratings Parameter Max Unit Supply Voltage VIN -0.3~20 V Switch Node Voltage VSW -0.3~VIN+0.5 V Boost Voltage VBS VSW -0.3~VSW+5 V All other pins -0.3~6 Operating Temperature Range Storage Temperature Range Lead Temperature (Soldering, 10s) V -40~85 O C -65~+150 O C 300 O C VER 1.2 1 ACE727C 600KHz, 16V, 2A Synchronous Step-Down Converter Packaging Type SOT23-6 PIN NO. Description 1 BS 2 GND 3 FB 4 EN 5 VIN Boostrap. A capacitor connected between SW and BS pins is required to form a floating supply across the high-side switch driver. Ground Adjustable version feedback input. Connect FB to the center point of the external resistor divider. Drive this pin to a logic-high to enable the IC. Drive to a logic-low to disable the IC and enter micro-power shutdown mode. Power supply Pin 6 SW Switching Pin Function Ordering information ACE727CGM + H Halogen - free Pb - free GM: SOT23-6 TYPICAL APPLICATION VER 1.2 2 ACE727C 600KHz, 16V, 2A Synchronous Step-Down Converter BLOCK DIAGRAM Electrical Characteristics Parameter Conditions Input Voltage Range Min Typ 3.5 UVLO Threshold Max Unit 16 V 2 Supply Current in Operation VEN = 2.0V, VFB = 1.1V 0.4 Supply Current in Shutdown VEN = 0V or VEN = GND 1 Regulated Feedback Voltage 4.5V≤VIN ≤18V 0.588 0.6 V 0.6 mA μA 0.612 V High-side Switch On Resistance 90 mΩ Low-side Switch On Resistance 70 mΩ VEN = 0V, VSW = 0V 0 Upper Switch Current Limit Minimum Duty Cycle 4.2 A Oscillation Frequency 600 kHz Maximum Duty Cycle 92 % Minimum On Time Thermal Shutdown VFB = 0.6V 60 170 10 μA High-side Switch Leakage Current ns O C VER 1.2 3 ACE727C 600KHz, 16V, 2A Synchronous Step-Down Converter DETAILED DESCRIPTION Internal Regulator The ACE727C is a current mode step down DC/DC converter that provides excellent transient response with no extra external compensation components. This device contains an internal, low resistance, high voltage power MOSFET, and operates at a high 600K operating frequency to ensure a compact, high efficiency design with excellent AC and DC performance. Error Amplifier The error amplifier compares the FB pin voltage with the internal FB reference (VFB) and outputs a current proportional to the difference between the two. This output current is then used to charge or discharge the internal compensation network to form the COMP voltage, which is used to control the power MOSFET current. The optimized internal compensation network minimizes the external component counts and simplifies the control loop design. Internal Soft-Start The soft-start is implemented to prevent the converter output voltage from overshooting during startup. When the chip starts, the internal circuitry generates a soft-start voltage (SS) ramping up from 0V to 0.6V. When it is lower than the internal reference (REF), SS overrides REF so the error amplifier uses SS as the reference. When SS is higher than REF, REF regains control. The SS time is internally fixed to 1ms. Over-Current-Protection and Hiccup The ACE727C has cycle-by-cycle over current limit when the inductor current peak value exceeds the set current limit threshold. Meanwhile, output voltage starts to drop until FB is below the Under-Voltage (UV) threshold, typically 30% below the reference. Once a UV is triggered, the ACE727C enters hiccup mode to periodically restart the part. This protection mode is especially useful when the output is dead-short to ground. The average short circuit current is greatly reduced to alleviate the thermal issue and to protect the regulator. The ACE727C exits the hiccup mode once the over current condition is removed. Startup and Shutdown If both VIN and EN are higher than their appropriate thresholds, the chip starts. The reference block starts first, generating stable reference voltage and currents, and then the internal regulator is enabled. The regulator provides stable supply for the remaining circuitries. Three events can shut down the chip: EN low, VIN low and thermal shutdown. In the shutdown procedure, the signaling path is first blocked to avoid any fault triggering. The COMP voltage and the internal supply rail are then pulled down. The floating driver is not subject to this shutdown command. VER 1.2 4 ACE727C 600KHz, 16V, 2A Synchronous Step-Down Converter APPLICATIONS INFORMATION Setting Output Voltages The external resistor divider is used to set the output voltage (see Typical Application on page 1). The feedback resistor R1 also sets the feedback loop bandwidth with the internal compensation capacitor. Choose R1 to be around 100kΩ for optimal transient response. R2 is then given by: Selecting the Inductor A 4.7μH to 22μH inductor with a DC current rating of at least 25% percent higher than the maximum load current is recommended for most applications. For highest efficiency, the inductor DC resistance should be less than 15mΩ. For most designs, the inductance value can be derived from the following equation. Where ΔIL is the inductor ripple current. Choose inductor ripple current to be approximately 30% if the maximum load current, 2A. The maximum inductor peak current is: Under light load conditions below 100mA, larger inductance is recommended for improved efficiency. VER 1.2 5 ACE727C 600KHz, 16V, 2A Synchronous Step-Down Converter Selecting the Output Capacitor The output capacitor (C2) is required to maintain the DC output voltage. Ceramic, tantalum, or low ESR electrolytic capacitors are recommended. Low ESR capacitors are preferred to keep the output voltage ripple low. The output voltage ripple can be estimated by: Where L is the inductor value and RESR is the equivalent series resistance (ESR) value of the output capacitor. In the case of ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance. The output voltage ripple is mainly caused by the capacitance. For simplification, the output voltage ripple can be estimated by: In the case of tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency. For simplification, the output ripple can be approximated to: The characteristics of the output capacitor also affect the stability of the regulation system. The ACE727C can be optimized for a wide range of capacitance and ESR values. VER 1.2 6 ACE727C 600KHz, 16V, 2A Synchronous Step-Down Converter ELECTRICAL PERFORMANCE Tested under, L=4.7uH, TA=25℃, unless otherwise specified Efficiency vs. Iout Efficiency vs. Iout (Vout=1.2V) (Vout=3.3V) Iout (A) Iout (A) Efficiency vs. Iout Vout vs. Iout (Vout=5.0V) (Vout=1.2V) Iout (A) Iout (A) VER 1.2 7 ACE727C 600KHz, 16V, 2A Synchronous Step-Down Converter ELECTRICAL PERFORMANCE Tested under, L=4.7uH, TA=25℃, unless otherwise specified Vout vs. Iout Vout vs. Iout (Vout=3.3V) (Vout=5.0V) Iout (A) Efficiency vs. Vin Iout=1A Vin (V) Iout (A) Vout vs. Vin Iout=1A Vin (V) VER 1.2 8 ACE727C 600KHz, 16V, 2A Synchronous Step-Down Converter Packing Information SOT23-6 UNIT: mm VER 1.2 9 ACE727C 600KHz, 16V, 2A Synchronous 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 1.2 10