AME5258/5258A Evaluation Board User Guide 1. General Descriptions The AME5258/5258A is 600mA /800mA, synchronous step-down DC/DC converter with integrated a main switch and a synchronous rectifier without the need for external Schottky diode. The PWM operation is able to vary the duty ratio linearly from 0 up to 100%. This device, available in SOT-25 package, is ideal suited for single Li-Ion battery powered applications or other portable applications that require small board space. 2. Features ● High Efficiency - Up to 96% ● Guaranteed 600mA Output Current ● 2.5V to 5.5V Input Voltage Range ● 1.5MHz Constant Frequency Operation ● No Schottky Diode Required ● Low Dropout Operation: 100% Duty Cycle ● 0.6V Reference Allows Low Output Voltages ● Shutdown Mode Draws<1µA Supply Current ● Current Mode Operation for Excellent Line and Load Transient Response ● Over Temperature Protection ● Internal Soft Start ● Space Saving 5-Pin SOT-25 Package 3. Applications ● Cellular Phones ● USB Devices ● Digital Cameras ● MP3 Players ● Portable Electronics ● LDO Replacement Rev. A/01-2010 4. Evaluation Board Schematic (4.1) AME5258/5258A Typical Schematic Figure 1. (4.2) AME5258 Typical Schematic for 1.8V Application Figure 2. Rev. A/01-2010 5. Bill of Materials BOM for item (4.2) Location Q’ty Value Description Part No. Manufacture Package Cin 1 4.7µF/16V Ceramic Capacitor C3216X5R1A475K TDK 1206 Cout 1 10µF/6.3V Ceramic Capacitor CL31A106MQHNNNE Samsung 1206 C3 1 22pF/50V Ceramic Capacitor CL10C220JB8NNNC Samsung 0603 R1 1 100KΩ Chip Resistor MCR10EZHF1003 Rohm 0805 R2 1 887KΩ Chip Resistor MCR10EZHF8873 Rohm 0805 R3 1 442KΩ Chip Resistor MCR10EZHF4423 Rohm 0805 L1 1 2.2uH Inductor SD52-2R2 COOPER - U1 1 - AME5258-BEVADJ AME SOT-25 PCB 1 - Blank PCB TM081208 Rev.A AME - 2 - Terminal Blocks EK381V-02P DINKLE - EN 1 - Switch TS-006S-5-190g HSUAN YI - - 5 - Test Pin JT-1P-CIR PINGOOD - - 4 - Plastic Screw S-306 PINGOOD - - 4 - Spacer Support H-6 PINGOOD - Vin&GND, Vout&GND 1.5MHz, 600m Buck Converter 6. Operating Instructions (6.1) Connect Vin to the positive point of DC power supply and GND to supply ground. (6.2) Connect Vout to the positive point of E-load and GND to supply ground or parallel an appropriate resistor to pull up the loading. (6.3) Importing a logic signal to EN pin will enable the AME5258/5258A. Logic high (VEN>1.4V) switches on AME5258/5258A, logic low puts it into low current shutdown mode. 7. Application Information (7.1) Setting Output Voltage In the adjustable version, the regulated output voltage is set with an external resistor divider (R2 and R3 in Figure 1.) from the output to the VFB pin and is determined by: VOUT = VFB × (1 + R2 ) R3 Where VFB = 0.6V for AME5258 and AME5258A. Rev. A/01-2010 (7.2) Capacitor Selection (7.2.1) Input Capacitor Selection The input capacitor should be chosen to handle the RMS ripple current of a buck converter. The RMS current is calculated as the following equation: I RMS = I OUT ( MAX ) × VOUT VIN × −1 VIN VOUT Select the voltage rating should be 1.25 to 1.5 times greater than the maximum input voltage. Multi-layer ceramic capacitors, which have very low ESR and can easily handle high RMS ripple current. 4.7µF to 10µF ceramic capacitor is adequate for most applications. X5R and X7R types are suitable because of their wider voltage and temperature ranges. To ensure stable operation, Cin should be placed as close to the IC as possible. (7.2.2) Output Capacitor Selection The output ripple voltage ∆Vout of a buck converter is calculated as the following equations: ∆VOUT = ∆I L × ( ESRCOUT + 1 ) 8 × f SW × COUT Where: ∆Vout is the output ripple voltage. ∆IL is the output ripple current. fsw is the switching frequency. Cout is the output capacitance. ESRout is the Equivalent Series Resistance of the output capacitor. A 10µF ceramic capacitor is found adequate for output filtering in this application. (7.3) Inductor Value Calculation The inductor ripple current for a synchronous step-down converter is calculated by using the following equation: ∆I L = VIN − VOUT VOUT × L × f SW VIN Rev. A/01-2010 Where: ∆IL is the inductor ripple current. fsw is the switching frequency. L1 is the inductance. For most applications, the value of the inductor will fall in the range of 1µH to 4.7µH. (7.4) Board Layout Considerations High frequency switching regulators require very careful layout of components in order to get stable operation and low noise. A good PCB layout could make AME5258/5258A working perfect to achieve the best performance. (7.5) PCB Layout Example The PCB layout example is for standard step-down converter application with AME5258/5258A device. It proves this evaluation board can achieve reliable performance. It follows the layout guidelines below. (7.5.1) Keep the power traces, consisting of the GND trace, the SW trace and the Vin trace short and wide. (7.5.2) The inductor and SW pin should be kept extremely short. (7.5.3) The input capacitor should be placed close to the IC’s Vin and GND pin. (7.5.4) The feedback components R2, R3 and C3 must be kept close to the IC’s FB pin to prevent noise injection on the FB pin trace and keeping far away from SW node. Connect feedback trace behind the output capacitors. Rev. A/01-2010 3 SW 2 GND 4 IN 5 FB 1 EN Figure 3. AME5258/5258A Evaluation Board PCB Layout Rev. A/01-2010