AME5142/5142A/5142B Evaluation Board User Guide 1. General Descriptions The AME5142/AME5142A/AME5142B 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 92%. This device, available in a 6-pin SOT-26 package, provides a backlight solution with minimal external components. 2. Features ● Input voltage: 2.7V to 5.5V ● Output voltage: Vcc to 26V ● Duty ratio: 0% to 92% PWM control ● Oscillation frequency: 1.2MHz ● Current limit and Enable function ● Thermal shutdown function ● Built-in internal SW N-channel MOS ● SOT-25 and SOT-26 Package 3. Applications ● LCD Bias ● Battery Backup ● Hand-held Computers ● Smart Phone ● Digital Cameras ● Digital Picture Frame 4. Evaluation Board Schematic GND GND IN (4.1) AME5142 Typical Schematic Figure 1 Rev. B /01-2010 (4.2) AME5142 Typical Schematic for 12V Application L1 5V 4.7uH C1 4.7uF 12V D1 RSX101VA-30 C6 10uF C3 0.1uF SW IN GND EN 100KΩ EN GND IN C4 100pF R1 C7 0.1uF 442KΩ FB AME5142 EN R2 R3 5.6KΩ Figure 2 GND GND IN (4.3) AME5142 Typical Schematic for WLED Driver (6S1P) Application Figure 3 Rev. B /01-2010 5. Bill of Materials BOM for item (4.2) Nomenclature Q’ty Value Description Part No. Manufacturer Package C1 1 4.7uF/ 6.3V Ceramic Capacitor C1608Y5V0J475ZT TDK 1608 C3,C7 1 0.1uF/ 50V Ceramic Capacitor C1608X7R1H104KT TDK 1608 C4 1 100pF/ 50V Ceramic Capacitor C1608C0G1H101JT TDK 1608 C6 1 10uF/ 25V Ceramic Capacitor C3225X7R1E106KT TDK 3225 R1 1 100KΩ Chip Resistor CR0805F100KP05 SYNTAX 0805 R2 1 442KΩ Chip Resistor CR0805F442KP05 SYNTAX 0805 R3 1 5.6KΩ Chip Resistor CR-05FL7---5K6 SYNTAX 0805 L1 1 4.7uH Inductor SD52-4R7-R COOPER SD52 D1 1 30V/1A Schottky Rectifier RSX101VA-30 ROHM SMA U1 1 - AME5142AEEVADJZ AME SOT-25 PCB 1 - Blank PCB TM081001 Rev.B AME - 2 - Terminal Blocks EK381V-02P DINKLE - EN 3 - Pin Header YD-TECH 1x40 12M/M - 6 - Test Pin JT-1P-CIR PINGOOD - - 4 - Plastic Screw S-306 PINGOOD - - 4 - Spacer Support H-6 PINGOOD - Value Description Part No. Manufacturer Package Vin&GND, Vout&GND 1.2MHz, 25V Boost Converter BOM for item (4.3) Nomenclature Q’ty C1 1 4.7uF/ 6.3V Ceramic Capacitor C1608Y5V0J475ZT TDK 1608 C3,C7 1 0.1uF/ 50V Ceramic Capacitor C1608X7R1H104KT TDK 1608 C6 1 1uF/ 16V Ceramic Capacitor C1608X5R1C105KT TDK 1608 R1 1 100KΩ Chip Resistor CR0805F100KP05 SYNTAX 0805 R4 1 0Ω Chip Resistor RM-0 SYNTAX 0805 R5 1 7.5Ω Chip Resistor FCR05-F-T-0750 PDC 0805 L1 1 4.7uH Inductor SD52-4R7-R COOPER SD52 D1 1 30V/1A Schottky Rectifier RSX101VA-30 ROHM SMA D2~D7 6 - White LED LT8AW1-54-UEE3-TE Ledtech 0603 U1 1 - 6S WLED Driver AME5142AEEVADJZ AME SOT-25 PCB 1 - Blank PCB TM081001 Rev.B AME - 2 - Terminal Blocks EK381V-02P DINKLE - Vin&GND, Vout&GND Rev. B /01-2010 Nomenclature Q’ty EN Value Description Part No. Manufacturer Package YD-TECH 1x40 12M/M 3 Pin Header 6 Test Pin JT-1P-CIR PINGOOD 4 Plastic Screw S-306 PINGOOD 4 Spacer Support H-6 PINGOOD 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 logic signal to EN pin will enable the AME5142/AME5142A/AME5142B. Logic high (VEN>1.5V) turns on AME5142/AME5142A/AME5142B, logic low puts it into low current shutdown mode. 7. Application Information (7.1) Setting Output Current The regulated output current is set with an external resistor divider (R5 in Figure 1.) from the output to the VFB pin and is determined by: I OUT = VFB R5 To prevent stray capacitance and noises, locate resistors R5 close to AME5142/AME5142A /AME5142B. The external resistor sets the output current table as below: IOUT R5 20mA 7.5Ω 40mA 3.75Ω 60mA 2.5Ω 80mA 1.875Ω (7.2) Capacitor Selection 4.7uF input capacitor can reduce input ripple. For better voltage stability, to increase the input capacitor value or using LC filter is feasible. 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 Rev. B /01-2010 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 (7.3.2) Calculating Inductor The recommended value of inductor for AME5142/AME5142A/AME5142B/5142A application is 2.2uH ~ 10uH. 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 AME5142/AME5142A/AME5142B work its best performance. (7.5) PCB Layout Example This PCB layout example uses the AME5142/AME5142A/AME5142B for 6 LEDs in one string application. The placement is suitable and smooth, and follows the layout guide lines. Rev. B /01-2010 (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 C6, C7 and C8 signal path should be kept extremely short. (7.5.4) The feedback components R2, R3 and C4 must be kept close to the FB pin of U1 to prevent noise injection on the FB pin trace and keeping far away from SW node. Test Pin GND EN IN Net1 GND Net1 EN LED R1 EN Vo EN IN 1210 OVP D23 0805 FB D29 D35 Vout Vo D13 GND D36 D31 GND D36 D37 D37 D31 D25 R9 GND D30 R10 GND D25 R8 R7 R6 R5 GND D19 D19 D13 R4 D30 D37 R4 FB R4 D24 D18 D31 GND R3 C5 D24 D35 D29 GND D12 D6 D18 D25 GND D12 D19 R4 D13 FB 0805 D7 FB D1 D6 FB D23 D36 FB D34 D34 D35 D17 D17 D11 D5 Vo D30 Vo D24 SW D33 D33 D34 D28 D28 D29 D11 D22 D23 GND D32 D33 D27 D27 D28 D16 D22 D10 D22 D26 D27 D21 Vo D21 D16 D18 SW D15 D10 D17 C8 D16 Vo D5 C6 GND D21 R2 C4 D12 SW Vo D6 GND GND D11 D5 GND 1210 D15 D4 GND D20 D14 D15 Vo D32 Vo IN C3 D10 GND U1 0603 1210 GND D9 D4 IN IN D3 D4 0603 IN C1 D9 D3 Vin C7 C2 IN D9 Vo D26 D32 D8 D3 Vo D20 D26 D2 D14 D20 D8 D14 D8 D2 Test Pin 6 places 1210 GND L1 Vo Vo D2 GND GND Screw Spacer 4 places Figure 4 (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, RSX101VA-30 is chosen, with 30V reverse voltage, 1A forward current, and around 0.5V forward voltage drop. The freewheeling diode should be place close to the SW pin of the AME5142/AME5142A/ AME5142B to minimize ring due to trace inductance. Rev. B /01-2010