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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 JP1 VCC Jumper U2 VBAT C3 1uF 1 2 3 IN GND SHDN BYP G914C 4 C5 0.1uF 4 SHDN FB 3 FB U1 G5103 LED3 OUT 5 C4 1uF +3VDC VCC SW LED1 C2 0.1uF LED2 D1 MBR0530
2 ~ 4 White LED
5
VCC
VCC J1 1 2 3 4 BATT VBAT
VSS
SW
1
2
C1 4.7uF
1
+3VDC U3 1 VDD 2 PWM Dim GP5 3 GP4 4 GP3
SW1 VSS GP0 GP1 GP2 8 7 6 5 DIM Low SW2 DIM High SW3 FREQ PWM Dim +3VDC
2
LED4
R3 240K_1% R4 620K_1% R2 120K_1% VISEN R1 27_1%
PIC12C508
18.5mA
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. Components List
Designation
R1 R2 R3 R4 C1 C2 C3 C4 C5
EV5103-10
Qty
1 1 1 1 1 1 1 1 1
Value& P/N
27_1% 120K_1% 240K_1% 620K_1% 4.7F 0.1F 1F 1F 0.1F 10H/0.5A IDC (LQH32CN100K31) 10H/0.5A IDC (976AS-100M) 0.5A/30V(MBR0530) G5103 G914C PIC12C509A NSCW100
Description
Current Sense Resistor Feedback Resistor (recommend) PWM Dimming Control Bias Resistor PWM Dimming Control Mixer Resistor Input Capacitor Output Capacitor Input Capacitor Output Capacitor Bypass Capacitor Inductor Inductor Std
Vendor
TAIYO YUDEN
MURATA TOKO
L1
1
D1 U1 U2 U3 SW1~3 LED1~4
1 1 1 1 3 4
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 4.7F 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 = 30 is feedback resistor, 120K is recommended. is PWM dimming control mixer resistor. The value is depended on PWM dimming control signal amplitude. R4= (VH - VL) / (0.6V / 120K). (maximum value, a little small value could be used) For 3.0V PWM control signal: R4= 3V / (0.6V / 120K) = 600K. For 3.3V PWM control signal: R4= 3.3V / (0.6V / 120K) = 660K. For 5.0V PWM control signal: R4= 5V / (0.6V / 120K) = 1M. R3: is PWM dimming control bias resistor. The value is depended on VBIAS voltage. R3=( VBIAS- VFB) /[(0.6V/120 K)+(VFB / R4)]. For 3VDC VBIAS:= (3.0V - 1.2V) / [(0.6V/120 K)+(1.2V / 600 K)] = 257 K. For 3.3VDC VBIAS:= (3.3V - 1.2V) / [(0.6V/120 K)+(1.2V / 660 K)] = 308 K For 5VDC VBIAS:= (5.0V - 1.2V) / [(0.6V/120 K)+(1.2V / 1000 K)] = 612 K 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 = 27, R2=120 K, R3=240K, R4=620K. When PWM signal is low: ILED = (1.2V - 120K x (((3V - 1.2V)/240K) - (1.2V/620K) - 30nA)) / 27 = 19.7mA When PWM signal is high: ILED = (1.2V - 120K x (((3V - 1.2V)/240K) - ((1.2V-3V)/620K) - 30nA)) / 27 = -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. How to Use This Demo Board
EV5103-10
LED driver circuit only in red rectangle Other circuit is for PWM dimming control demonstration.
Fig.2 J1: SW1: SW2: SW3: 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 210Hz 220Hz 230Hz 240Hz 250Hz 150Hz 160Hz 170Hz 180Hz 190Hz 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.
JP1: LEDs:
Jan 21, 2003
TEL: 886-3-5788833 http://www.gmt.com.tw
4

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