Global Mixed-mode Technology Inc. EV5103-10 G5103 White LED Demo Board V1.0 Introduction G5103 is a step-up (boost) DC/DC converter, using constant peak inductor current and minimum OFF time PFM topology. It could output up to 16V and drive 20mA from a 2.5V ~ 5.5V input power source, such as a Li-Ion battery. G5103 is suitable for series 2~4 white LED driver application because its maximum 16V output capability. This solution possess high efficiency about 84% when drive 4 white LED at 20mA output LED current with a 3.6V Li-Ion battery power input. This demo board could demonstration: 1. Drive 2 ~ 4 white LED @ 20mA. 2. 200Hz PWM dimming control. 3. Only need 3.0V ~ 5.5V power source. A Li-Ion battery is a good power source. 200Hz PWM Dimming White LED Driver Demo Schematic L1 10uH/0.5A VCC C4 1uF GND 3 SHDN BYP J1 C1 4.7uF LED2 4 C5 0.1uF G914C VBAT LED1 C2 0.1uF 4 SHDN FB +3VDC U3 1 VDD 2 PWM Dim GP5 3 GP4 4 GP3 SW1 VSS GP0 GP1 GP2 PIC12C508 8 7 6 5 LED3 U1 G5103 2 BATT 3 FB VSS 1 2 3 4 OUT 2 ~ 4 White LED SW IN 2 2 1 C3 1uF 5 VBAT 5 D1 MBR0530 SW VCC VCC 1 +3VDC 1 U2 JP1 VCC Jumper LED4 DIM Low SW2 +3VDC DIM High SW3 PWM Dim FREQ R3 240K_1% R4 620K_1% R2 120K_1% 18.5mA VISEN R1 27_1% PWM Dimming Control Introduction SW1: Dimming dark ( minimum dimming duty = 0%) SW2: Dimming light ( maximum dimming duty = 100%) SW3: Change PWM dimming frequency ( 150Hz 250Hz) Fig.1 Jan 21, 2003 TEL: 886-3-5788833 http://www.gmt.com.tw 1 Global Mixed-mode Technology Inc. EV5103-10 Components List Designation Qty Value& P/N Description R1 1 27Ω_1% Current Sense Resistor R2 1 120KΩ_1% Feedback Resistor (recommend) R3 1 240KΩ_1% PWM Dimming Control Bias Resistor R4 1 620KΩ_1% PWM Dimming Control Mixer Resistor C1 1 4.7µF Input Capacitor C2 C3 C4 C5 1 1 1 1 0.1µF 1µF 1µF 0.1µF Output Capacitor Input Capacitor Output Capacitor Bypass Capacitor L1 1 D1 U1 1 1 U2 U3 SW1~3 LED1~4 1 1 3 4 10µH/0.5A IDC (LQH32CN100K31) 10µH/0.5A IDC (976AS-100M) 0.5A/30V(MBR0530) G5103 G914C PIC12C509A NSCW100 Vendor Std TAIYO YUDEN Inductor MURATA Inductor TOKO Schottky Diode ON Semi Micro Power Step-up DC/DC Converter Global Mixed-Mode Technology Mirco power LDO regulator. VOUT=3.0V http://www.gmt.com.tw 8 bits micro-controller Miocrochip Push button switch Std White LED NICHIA corporation Circuit Description The demo board is configured as a constant current supply. Current regulation is accomplished by regulating the voltage across a current sense resistor R1. For dimming the LEDs is to inject a pulse width modulated (PWM) voltage for analog dimming. With this method, the PWM control voltage is converted to its equivalent analog control voltage. The demo board is designed so that the negative duty cycle from 0% to 100% varies the LED current from 0mA to 20mA. The output current increases as the duty cycle increases. Use the equation below to calculate the correctly resistor values. VBAT: VBIAS: R1: R2: R4: Li-Ion battery power input, bypass to ground with a 4.7µF MLCC capacitor. +3.0VDC provide a PWM dimming DC bias voltage. It is generated by G914C from VBAT. is LED current sense resistor. R1= 0.60V / ILED,MAX = 0.60V / 20mA = 30Ω is feedback resistor, 120KΩ is recommended. is PWM dimming control mixer resistor. The value is depended on PWM dimming control signal amplitude. R4= (VH - VL) / (0.6V / 120KΩ). (maximum value, a little small value could be used) For 3.0V PWM control signal: R4= 3V / (0.6V / 120KΩ) = 600KΩ. For 3.3V PWM control signal: R4= 3.3V / (0.6V / 120KΩ) = 660KΩ. For 5.0V PWM control signal: R4= 5V / (0.6V / 120KΩ) = 1MΩ. R3: is PWM dimming control bias resistor. The value is depended on VBIAS voltage. R3=( VBIAS– VFB) /[(0.6V/120 KΩ)+(VFB / R4)]. For 3VDC VBIAS:= (3.0V – 1.2V) / [(0.6V/120 KΩ)+(1.2V / 600 KΩ)] = 257 KΩ. For 3.3VDC VBIAS:= (3.3V – 1.2V) / [(0.6V/120 KΩ)+(1.2V / 660 KΩ)] = 308 KΩ For 5VDC VBIAS:= (5.0V – 1.2V) / [(0.6V/120 KΩ)+(1.2V / 1000 KΩ)] = 612 KΩ After choose suitable resistors, designer should check ILED again. Jan 21, 2003 TEL: 886-3-5788833 http://www.gmt.com.tw 2 Global Mixed-mode Technology Inc. EV5103-10 When PWM dimming signal is low (almost equal to 0V): ILED = VR1 / R1 VR1 = VFB – VR2 VR2 = IR2 x R2 IR2 = IR3 – IR4 - IFB = (VR3 / R3) – (VR4 / R4) - IFB = ((VBIAS – VFB)/R3) – (VFB/R4) - IFB ILED = (VFB – R2 x (((VBIAS – VFB)/R3) – (VFB/R4) - IFB)) / R1 ILED should be the design full current. When PWM dimming signal is high (almost equal to VPWM_H): ILED = VR1 / R1 VR1 = VFB – VR2 VR2 = IR2 x R2 IR2 = IR3 – IR4 - IFB = (VR3 / R3) – (VR4 / R4) - IFB = ((VBIAS – VFB)/R3) – ((VFB - VPWM_H)/R4) - IFB ILED = (VFB – R2 x (((VBIAS – VFB)/R3) – ((VFB - VPWM_H)/R4) - IFB)) / R1 ILED should be a little negative current to make sure that LED is full dark. In this demo board, GMT choose R1 = 27Ω, R2=120 KΩ, R3=240KΩ, R4=620KΩ. When PWM signal is low: ILED = (1.2V – 120KΩ x (((3V – 1.2V)/240KΩ) – (1.2V/620KΩ) – 30nA)) / 27Ω = 19.7mA When PWM signal is high: ILED = (1.2V – 120KΩ x (((3V – 1.2V)/240KΩ) – ((1.2V-3V)/620KΩ) – 30nA)) / 27Ω = -1.79mA U2: U3: G914C is a micro power LDO regulator that make by GMT. It could regulate a +3VDC from a +3V ~ +5.5V power source. The +3VDC provide as VBIAS for PWM dimming bias voltage, and provide as the power of U3. PIC12C509A is a 8bit micro controller that make by Microship. It is programmed as a PWM dimming signal generator, and monitor 3 push button to change PWM duty and frequency for dimming control. Note: You need download the hex code to program a blank new PIC12C509A before solder it on demo board. You could download this hex code from GMT web site http://www.gmt.com.tw Jan 21, 2003 TEL: 886-3-5788833 http://www.gmt.com.tw 3 Global Mixed-mode Technology Inc. EV5103-10 How to Use This Demo Board LED driver circuit only in red rectangle Other circuit is for PWM dimming control demonstration. Fig.2 J1: SW1: SW2: SW3: JP1: LEDs: is an input power connector. +BAT means positive side. The valid voltage range is from +3.0 to +5.5V. one cell Li-Ion battery or 3 cell NiCd or NiMH battery or adjustable power supply are good power source. is a push button switch, every click makes LEDs a little darker until 100% light. is a push button switch, every click makes LEDs a little lighten until full dark. is a push button switch, every click change dimming PWM frequency from 200Hz Æ 210Hz Æ 220Hz Æ 230Hz Æ 240Hz Æ 250Hz Æ 150Hz Æ 160Hz Æ 170Hz Æ 180Hz Æ 190Hz Æ 200Hz. But the change could not be observed be human eyes. Only a oscilloscope could shows the difference. is a jumper, which must be close for normal operating. You should open this jumper to measure input current if you want to measure the efficiency of this demo board. LED1 ~ LED4 has solder with white LED. Jan 21, 2003 TEL: 886-3-5788833 http://www.gmt.com.tw 4