AME5252 Evaluation Board User Guide 1. General Descriptions The AME5252 is a dual channel, synchronous step-down DC/DC converter with integrated a main switch and a synchronous rectifier of each channel 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-10B 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% ● Internal soft start ● 1.5MHz Constant Frequency Operation ● High Switch Current: 1A on Each Channel ● No Schottky Diode Required ● Low RDSON Internal Switches: 0.35Ω ● Current Mode Operation for Excellent Line and Load Transient Response ● Short-Circuit Protected ● Low Dropout Operation: 100% Duty Cycle ● Ultra low Shutdown Current: IQ<1µA ● Output Voltages from 5V down to 0.6V ● Power-On Reset Output ● Externally Synchronizable Oscillator 3. Applications ● PDAs/Palmtop PCs ● Portable Media Players ● Digital Cameras ● PC Cards ● Cellular Phones ● Wireless and DSL Modems Rev. A/01-2010 4. Evaluation Board Schematic (4.1) AME5252 Typical Schematic Figure 1. (4.2) AME5252 Typical Schematic for 1.5V/3.3V Output Voltage Application Vin 5V R7 100K C5 optional Cin2 10uF Cin1 0.1uF SYNC EN2 9 3 EN2 6 Vout2 3.3V/600mA L2 CF2 22pF C3 0.1uF IN U1 SW1 AME5252-AVBADJ VFB2 VFB1 GND 8 4 Vout1 1.5V/600mA L1 2.2uH 1 R1 475K PGND 5 C2 10uF EN2 PORB SW2 10 R5 100K 2 SYNC 7 2.2uH R3 887K R6 100K EN1 11 R4 196K CF1 22pF C1 10uF C4 0.1uF R2 316K Figure 2. Rev. A/01-2010 5. Bill of Materials BOM for item (4.2) Location Q’ty Value Description Part No. Cin2,C1, C2 3 10µF/6.3V Ceramic Capacitor CL31A106MQHNNNE Samsung 1206 Cin1, C3, C4 3 0.1µF/50V Ceramic Capacitor C2012X7R1H104K TDK 0805 CF1, CF2 2 22pF/50V Ceramic Capacitor CL10C220JB8NNNC Samsung 0603 R5, R6, R7 3 100KΩ Chip Resistor CR-05FL7-100K Viking 0805 R3 1 887KΩ Chip Resistor CR-05FL7-887K Viking 0805 R1 1 475KΩ Chip Resistor CR-05FL7-475K Viking 0805 R4 1 196KΩ Chip Resistor CR-05FL7-196K Viking 0805 R2 1 316KΩ Chip Resistor CR-05FL7-316K Viking 0805 L1 2 2.2uH Inductor SD52-2R2 COOPER - U1 1 - AME5252-AVBADJ AME DFN-10B PCB 1 - Blank PCB TM090701 Rev.B AME SYNC 1 - Pin Header - - - 8 - Copper Pillar - - - EN1, EN2 2 - Switch TS-006S-5-190g HSUAN YI - - 4 - Test Pin JT-1P-CIR PINGOOD - - 4 - Plastic Screw S-306 PINGOOD - - 4 - Spacer Support H-6 PINGOOD - Vin, Vout, POR, GND Dual 1.5MHz, 600mA Buck Converter Manufacture Package 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 AME5252. Logic high (VEN>1.5V) switches on AME5252, logic low puts it into low current shutdown mode. (6.4) The oscillation frequency can be synchronized to an external oscillator applied to SYNC pin and pulse skipping mode is automatically selected. Insert jumper SYNC into high or low if no external oscillator will be applied. Rev. A/01-2010 7. Application Information (7.1) Setting Output Voltage The regulated output voltage is set with an external resistor divider (R1 and R2 for channel one; R3 and R4 for channel two in Figure 1.) from the output to the VFB pin and is determined by: VOUT1 = VFB × (1 + R1 ) R2 VOUT 2 = VFB × (1 + R3 ) R4 Where VFB = 0.6V for AME5252. (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 Rev. A/01-2010 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 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 AME5252 working perfect to achieve the best performance. (7.5) PCB Layout Example The PCB layout example is for standard step-down converter application with AME5252 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. Rev. A/01-2010 (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, CF1 and R3, R4, CF2 must be kept close to the IC’s VFB1 pin and VFB2 pin respectively to prevent noise injection on the VFB pin trace and 9 EN2 8 PORB 7 SW2 6 SYNC 3 IN 4 SW1 5 GND 10 VFB2 2 EN1 1 VFB1 keeping far away from SW node. Connect feedback trace behind the output capacitors. Figure 3. AME522 Evaluation Board PCB Layout Rev. A/01-2010