AME5250 Evaluation Board User Guide 1. General Descriptions The AME5250 is 1A, 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 DFN-6D 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 95% ● Very Low 20µA Quiescent Current ● High efficiency in light load condition ● 2.5V to 5.5V Input Range ● Adjustable Output Voltages From 0.6V to Vin ● 1.0V, 1.2V, 1.5V, 1.6V, 1.8V, 2.5V and 3.3V Fixed/Adjustable Output Voltage ● 1A Output Current ● Low Dropout Operation: 100% Duty Cycle ● No Schottky Diode Required ● 1.5MHz Constant Frequency PWM Operation ● Small DFN-6D Package 3. Applications ● Cellular Telephones ● MP3 Players ● Personal Information Appliances ● Portable Instruments ● Wireless and DSL Modems Rev. A/01-2010 4. Evaluation Board Schematic (4.1) AME5250 Typical Schematic Figure 1. (4.2) AME5250 Typical Schematic for 1.8V Output Voltage Application Vin 5V IN U1 SW 2.2uH REN 100K EN Cin 4.7uF EN Switch Vout 1.8V/1A L1 FB AME5250-AVYADJ C1 22pF R1 150K Cout 10uF R2 75K 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/6.3V Ceramic Capacitor CL31A106MQHNNNE Samsung 1206 Cout 1 10µF/6.3V Ceramic Capacitor CL31A106MQHNNNE Samsung 1206 C1 1 22pF/50V Ceramic Capacitor CL10C220JB8NNNC Samsung 0603 REN 1 100KΩ Chip Resistor CR-05FL7-100K Viking 0805 R1 1 150KΩ Chip Resistor CR-05FL7-150K Viking 0805 R2 1 75KΩ Chip Resistor CR-05FL7-75K Viking 0805 L1 2 2.2uH Inductor CDRH5D16NP-2R2NC Sumida - U1 1 - AME5250-AVYADJ AME DFN-6D PCB 1 - Blank PCB TM091201 Rev.A AME - 4 - Copper Pillar - - - 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, Vout, POR, GND 1.5MHz, 1A 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 AME5250. Logic high (VEN>1.5V) switches on AME5250, 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 (R1 and R2 in Figure 1.) from the output to the VFB pin and is determined by: VOUT = VFB × (1 + R1 ) R2 Where VFB = 0.6V for AME5250. 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. Rev. A/01-2010 (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 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 AME5250 working perfect to achieve the best performance. (7.5) PCB Layout Example The PCB layout example is for standard step-down converter application with AME5250 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 R1, R2 and C1 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 Figure 3. AME5250 Evaluation Board PCB Layout Rev. A/01-2010