AME5144 Evaluation Board User Guide 1. General Descriptions The AME5144 is a non-synchronous step-up DC/DC converter with integrated N-channel Power MOS. The PWM operation is able to vary the duty ratio linearly from 0% up to 95%. This device, available in space saving with 8pin, 3mmx3mmx0.75mm DFN package, provides a backlight solution with minimal external components. 2. Features ● Input voltage: 2.6V to 5.5V ● Output voltage: Up to 37V ● Duty ratio: Up to 95% PWM control ● Oscillation frequency: 1MHz PWM Switching ● Current limit and Enable function ● 0.1uF Output Capacitor ● Soft Start Eliminates Inrush ● 0.3uA Shutdown Current ● Built-in internal SW N-channel MOS ● DFN-8C Package 3. Applications ● Cell Phones and Smart Phones ● PDAs, Palmtop and Wireless Handhelds ● E-Books and Subnotebooks ● White LED Display Backlighting 4. Evaluation Board Schematic (4.1) AME5144 Typical Schematic Figure 1 1/5 Rev. A /01-2010 (4.2) AME5144 Typical Schematic for 10S WLED Driver Application Figure 2 5. Bill of Materials BOM for item (4.2) Component Q’ty C2 1 C3,C5 Value Part No. Manufacturer Package 2.2uF/ 6.3V Ceramic Capacitor 1206B225K6R3C WALSIN 1206 2 0.1uF/ 50V Ceramic Capacitor 0805B104K500C WALSIN 0805 R1 1 13Ω Chip Resistor RM10FTN13R0 TA-I 0805 R2 1 100K Chip Resistor RM10JTN104 TA-I 0805 L1 1 10uH Inductor SD52-10R0-R COOPER SD52 D1 1 40V/0.2A Schottky Diode RB520S-40 ROHM EMD2 LED 10 - White LED LT8AW1-54-UEE3-TE Ledtech 0603 U1 1 - AME5144AVAADJ AME DFN-8C PCB 1 - Blank PCB TM080701 Rev. B AME - Vin&GND 1 - Terminal Blocks EK381V-02P DINKLE - DIMMING 1 - Pin Header - YD-TECH 1x40 12M/M Test Pin JT-1P-CIR PINGOOD 6 Description 37V Boost for 2~10 WLED Driver - 4 - Plastic Screw S-306 PINGOOD - - 4 - Spacer Support H-6 PINGOOD - 2/5 Rev. A /01-2010 6. Operating Instructions (6.1) Connect VDD to the power source’s positive output. (6.2) Connect GND to supply ground. (6.3) Applying a DC signal in the range of 0.24V to 1.65V to CTRL pin will control the LED current. 7. Application Information (7.1) Adjusting output LED Current An analog input (CTRL) and the sense-resistor values set the output current (R1 in Figure 1) that is determined by: I LED = VCTRL 5 × R1 To set maximum current of LED, calculate R1 when VCTRL is at its maximum as by: R1 = 1.65 5 × I LED (7.2) Capacitor Selection 2.2uF input capacitor can reduce input ripple. For better voltage stability, to increase the input capacitor value or using LC filter is feasible. 0.1uF output capacitor is sufficient to reduce output voltage ripple. For better voltage filtering, ceramic capacitors with low ESR are recommended. X5R and X7R types are suitable because of their wider voltage and temperature ranges. (7.3) Inductor Value Calculation A larger value of inductor will reduce the peak inductor current, resulting in smaller input ripple current, higher efficiency and reducing stress on the internal MOSFET. Calculate the required inductance value by the equation: (7.3.1) Calculating Duty cycle The Duty cycle can’t over the maximum duty of specification. D= VOUT + VDIODE − VIN VOUT + VDIODE − VSW 3/5 Rev. A /01-2010 (7.3.2) Calculating Inductor The recommended value of inductor for AME5144 applications is around 10uH~47uH. L≥ D × (V IN − VSW ) I 2 f sw × ( I CL − Load ) (1 − D ) Where: VDIODE is the forward voltage of Schottky VSW is (“switch current” x “switch on-Resistance”) L is the inductance. fsw is the switching frequency. ILoad is the LED current. (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 AME5144 work its best performance. (7.5) PCB Layout Example This PCB layout example uses the AME5144 for 10 LEDs in one string application. The placement is suitable and smooth, and follows the layout guide lines. (7.5.1) Use a ground plane under the switching regulator to minimize inter-plane coupling. (7.5.2) Using 20mil wide track for GND (as wide as possible), and all GND nodes are as close as possible. (7.5.3) The SW node, schottky diode D1 and output capacitor C3 signal path should be kept extremely short. 4/5 Rev. A /01-2010 3 Vout L1 Test Pin 6 Places R6 Vout 1 2 3 4 1 2 3 4 5 R4_1 9 8 7 6 5 GND R4_1 9 8 7 6 D1 IN SW 6 GND 5 COMP IN R4 Vout C5 IN 8 SW Vin 7 PGND SW R3 R3_1 COMP R3_1 Vout GND GND GND IN GND 4 CS 2 IN GND 1 OUT IN 3 CTRL C2 C1 CS U1 CTRL Vout 10 R5 11 12 13 GND R1 10 11 12 13 14 18 17 16 15 14 CS 18 17 16 15 R2 GND Screw & Spacer 4 Places GND GND GND GND 12 Vout C3 C4 COMP CTRL GND DIMMING Figure 3 (7.6) Freewheeling Diode Selection The freewheeling diode conduction time is longer than the N-channel Power MOS off time. Therefore, the diode parameters improve the overall efficiency. Use of schottky diodes as freewheeling rectifiers reduces diode reverse recovery time and the voltage drop across the diode is lower. For this design, RB520S-40 is chosen, with 40V reverse voltage, 0.2A forward current, and around 0.4V forward voltage drop. The freewheeling diode should be place close to the SW pin of the AME5144 to minimize ring due to trace inductance. (7.7) PWM Dimming Control A. Applying DC signal for CTRL pin 0.24V~1.65V of DC signal for CTRL pin will drive AME5144 action. B. Using PWN signal for CTRL pin The frequency range is from 200Hz to 30kHz, while 0% duty for minimum output and 100% duty for full current. 5/5 Rev. A /01-2010