Jan 21, 2003
TEL: 886-3-5788833
http://www.gmt.com.tw
1
EV5103-10
Global Mixed-mode Technology Inc.
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
10uH/0.5A
L1
27_1%
R1
120K_1%
R2
SW
MBR0530
D1
VC
C
5
SW
1
FB
3
SHDN
4
VS
S
2
G5103
U1
LED1
LED2
LED3
LED4
240K_1%
R3
620K_1%
R4
1
2
VCC Jumper
JP1
1
2
3
4
BATT
J1
VCC
PWM Dim
+3VDC
FB
VISEN
VDD
1
GP5
2
GP4
3
GP3
4
GP2
5
GP1
6
GP0
7
VSS
8
PIC12C508
U3
IN
1
OUT
5
SHDN
3
BYP
4
GND
2
G914C
U2
1uF
C3
VBAT
1uF
C4
0.1uF
C5
+3VDC
VBAT
VCC
4.7uF
C1
0.1uF
C2
+3VDC
DIM Low
SW1
PWM Dim
DIM High
SW2
FREQ
SW3
18.5mA
2 ~ 4 White LED
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
2
EV5103-10
Global Mixed-mode Technology Inc.
Components List
Designation Qty Value&
P/N
Description
Vendor
R1 1
27
_1%
Current Sense Resistor
R2 1
120K
_1%
Feedback Resistor (recommend)
R3 1
240K
_1%
PWM Dimming Control Bias Resistor
R4 1
620K
_1%
PWM Dimming Control Mixer Resistor
Std
C1 1
4.7F
Input
Capacitor
C2 1
0.1F
Output
Capacitor
C3 1
1F
Input
Capacitor
C4 1
1F
Output
Capacitor
C5 1
0.1F
Bypass
Capacitor
TAIYO YUDEN
10H/0.5A IDC
(LQH32CN100K31)
Inductor MURATA
L1 1
10H/0.5A IDC
(976AS-100M)
Inductor TOKO
D1
1 0.5A/30V(MBR0530) Schottky Diode
ON Semi
U1
1 G5103
Micro Power Step-up DC/DC Converter
U2
1 G914C
Mirco power LDO regulator. V
OUT
=3.0V
Global Mixed-Mode Technology
http://www.gmt.com.tw
U3
1 PIC12C509A
8 bits micro-controller
Miocrochip
SW1~3
3
Push button switch
Std
LED1~4
4 NSCW100
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.
V
BAT
:
Li-Ion battery power input, bypass to ground with a 4.
7
F MLCC capacitor.
V
BIAS
:
+3.0VDC provide a PWM dimming DC bias voltage. It is generated by G914C from V
BAT
.
R1:
is LED current sense resistor. R1= 0.60V / I
LED,MAX
= 0.60V / 20mA = 30
R2:
is feedback resistor, 120K
is recommended.
R4:
is PWM dimming control mixer resistor. The value is depended on PWM dimming control signal
amplitude. R4= (V
H
- V
L
) / (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 V
BIAS
voltage.
R3=( V
BIAS
V
FB
) /[(0.6V/120 K
)+(V
FB
/ R4)].
For 3VDC V
BIAS
:= (3.0V 1.2V) / [(0.6V/120 K
)+(1.2V / 600 K)] = 257 K.
For 3.3VDC V
BIAS
:= (3.3V 1.2V) / [(0.6V/120 K
)+(1.2V / 660 K)] = 308 K
For 5VDC V
BIAS
:= (5.0V 1.2V) / [(0.6V/120 K
)+(1.2V / 1000 K)] = 612 K
After choose suitable resistors, designer should check I
LED
again.
Jan 21, 2003
TEL: 886-3-5788833
http://www.gmt.com.tw
3
EV5103-10
Global Mixed-mode Technology Inc.
When PWM dimming signal is low (almost equal to 0V):
I
LED
= V
R1
/ R1
V
R1
= V
FB
V
R2
V
R2
= I
R2
x R2
I
R2
= I
R3
I
R4
- I
FB
= (V
R3
/ R3) (V
R4
/ R4) - I
FB
= ((V
BIAS
V
FB
)/R3) (V
FB
/R4) - I
FB
I
LED
= (V
FB
R2 x (((V
BIAS
V
FB
)/R3) (V
FB
/R4) - I
FB
)) / R1
I
LED
should be the design full current.
When PWM dimming signal is high (almost equal to V
PWM_H
):
I
LED
= V
R1
/ R1
V
R1
= V
FB
V
R2
V
R2
= I
R2
x R2
I
R2
= I
R3
I
R4
- I
FB
= (V
R3
/ R3) (V
R4
/ R4) - I
FB
= ((V
BIAS
V
FB
)/R3) ((V
FB
- V
PWM_H
)/R4) - I
FB
I
LED
= (V
FB
R2 x (((V
BIAS
V
FB
)/R3) ((V
FB
- V
PWM_H
)/R4) - I
FB
)) / R1
I
LED
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:
I
LED
= (1.2V 120K
x (((3V 1.2V)/240K) (1.2V/620K) 30nA)) / 27 = 19.7mA
When PWM signal is high:
I
LED
= (1.2V 120K
x (((3V 1.2V)/240K) ((1.2V-3V)/620K) 30nA)) / 27 = -1.79mA
U2:
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 V
BIAS
for PWM dimming bias voltage, and provide
as the power of U3.
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
4
EV5103-10
Global Mixed-mode Technology Inc.
How to Use This Demo Board
Fig.2
J1:
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.
SW1:
is a push button switch, every click makes LEDs a little darker until 100% light.
SW2:
is a push button switch, every click makes LEDs a little lighten until full dark.
SW3:
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.
JP1:
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.
LEDs:
LED1 ~ LED4 has solder with white LED.
LED driver circuit only
in red rectangle
Other circuit is for
PWM dimming control
demonstration.
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