Global Mixed-mode Technology Inc.
G5121
Fixed Frequency White LED Step-Up Converter
Features
Inherently Matched LED Current
High Efficiency: 87%
Drives Up to Five LEDs from 2.5V Supply
24V Internal Power Switch
Fast 1MHz Switching Frequency
Uses Tiny 1mm Tall Inductors
Requires Only 1µF Output Capacitors
19.5V Over Voltage Protection
SOT-23-6 Package
General Description
The G5121 is a step-up DC/DC converter specifically
designed to drive up to 5 series white LEDs with con-
stant current. Series connection of the LEDs provides
identical LED currents resulting in uniform brightness
and eliminates the need for ballast resistors. The
G5121 switches at 1MHz, allowing the use of tiny ex-
ternal components. A low 0.254V feedback voltage
minimizes power loss in the current setting resistor for
high efficiency. The OVP pin monitors the output volt-
age and turns off the converter whenever the LEDs
are open.
The G5121 is available in low profile SOT-23-6 pack-
age.
Applications
White LED Backlight Display for PDA
Pocket PC
Smart Phones
Handheld Devices
Cellular Phones
Ordering Information
ORDER
NUMBER
G5121TB1U
MARKING
5121x
TEMP.
RANGE
-40°C ~ +85°C
PACKAGE
(Pb free)
SOT-23-6
Note:
TB : SOT23-6
U: Tape & Reel
Pin Configuration
Typical Application Circuit
L1
V
IN
2.7V to 4.2V
D1
SW
1
6
VCC
VCC
4.7µH
SW
OVP
C2
1µF/25V
5 LEDs
GND
2
G5121
5
OVP
C1
4.7µF/6.3V
PWM Dimming
Waveform
G5121
SHDN
GND
FB
R
S
FB
3
SOT-23-6
4
SHDN
C1:TAIYO YUDEN, JMK212BJ475KD
C2:TAIYO YUDEN, TMK316BJ105KD
Ver: 1.1
Nov 17, 2005
TEL: 886-3-5788833
http://www.gmt.com.tw
1
Global Mixed-mode Technology Inc.
Absolute Maximum Ratings
VCC,
SHDN
to GND.….....................……-0.3V to +7V
FB to GND.....................….........................-0.3V to VCC
SW, OVP to GND……….……..…………..-0.3V to +24V
Operating Temperature.….…………….....-40°C to 85°C
G5121
Junction Temperature......................….................125°C
Storage Temperature……....……..….….-65°C to 150°C
Reflow Temperature (soldering, 10sec)……...…260°C
ESD Rating (Human Body Model)………….….……2kV
Stress beyond those listed under “Absolute Maximum Rating” may cause permanent damage to the device.
Electrical Characteristics
(V
CC
=V
SHDN
=3.6V, T
A
=25°C)
PARAMETER
Input Voltage Range
Input Voltage UVLO
Over Voltage Protection Threshold
Over Voltage Protection Threshold
OVP Pin Input Current
Quiescent Current
trigger
release
V
ovp
= 16V
V
FB
= 0.3V (no switching)
V
FB
= 0.2V (switching)
V
SHDN
= 0V
Initial Accuracy
Temperature Coefficient
V
FB
= 0.2V
I
SW
= 150mA
V
SW
= 20V
CONDITIONS
MIN
2.5
1.7
18.5
13.5
---
---
---
---
TYP
---
MAX
6
2.3
21
16.5
UNITS
V
V
V
V
µA
µA
mA
µA
mV
ppm/°C
MHz
%
Ω
µA
mA
µs
V
V
2.0
19.5
15
40
80
---
60
120
2
1
264
---
0.1
254
100
1.0
---
FB Comparator Trip Point
Switching Frequency
Maximum Duty
Switch R
DS(ON)
Switch Leakage Current
Switch Current Limit
Soft Start Time
SHDN
Pin Voltage High
244
---
0.8
85
---
---
1.2
---
0.7
0.1
600
120
---
1.0
10
700
---
---
500
---
2
---
SHDN
Pin Voltage Low
---
0.8
Ver: 1.1
Nov 17, 2005
TEL: 886-3-5788833
http://www.gmt.com.tw
2
Global Mixed-mode Technology Inc.
Typical Performance Characteristics
(V
CC
= +3.6V, V
SHDN
= +3.6V, L=4.7µH, T
A
=25°C, unless otherwise noted.)
G5121
Stability for Driving 4 WLEDs
Stability for Driving 5 WLEDs
Stability for Driving 3 WLEDs
Stability for Driving 2 WLEDs
Inrush Current for Driving 5 WLEDs
Inrush Current for Driving 4 WLEDs
Ver: 1.1
Nov 17, 2005
TEL: 886-3-5788833
http://www.gmt.com.tw
3
Global Mixed-mode Technology Inc.
Typical Performance Characteristics
(continued)
Inrush Current for Driving 3 WLEDs
G5121
Inrush Current for Driving 2 WLEDs
OVP Waveform
Dimming Control for Driving 4 WLEDs
Efficiency vs. Load Current
90
80
70
Efficiency (%)
60
50
40
30
20
10
0
5
10
15
Load Current (mA)
20
25
5LEDs, C
O
=1µF
V
IN
=2.7V
V
IN
=3.6V
V
IN
=4.2V
Efficiency (%)
90
80
Efficiency vs. Load Current
V
IN
=2.7V
70
60
50
40
30
20
10
0
5
10
15
Load Current (mA)
V
IN
=3.6V
V
IN
=4.2V
4LEDs, C
O
=1µF
20
25
Ver: 1.1
Nov 17, 2005
TEL: 886-3-5788833
http://www.gmt.com.tw
4
Global Mixed-mode Technology Inc.
Typical Performance Characteristics
(continued)
Efficiency vs. Load Current
90
80
V
IN
=2.7V
70
Efficiency (%)
60
50
40
30
20
10
0
5
10
15
Load Current (mA)
20
25
3LEDs, C
O
=1µF
V
IN
=3.6V V
IN
=4.2V
Efficiency (%)
90
80
V
IN
=2.7V
70
60
50
40
30
20
10
0
5
10
15
Load Current (mA)
G5121
Efficiency vs. Load Current
V
IN
=3.6V V
IN
=4.2V
2LEDs, C
O
=1µF
20
25
IQ_NoSW vs. Input Voltage
130
120
110
100
90
80
70
60
50
40
30
20
10
0
2
2.5
3
3.5
4
4.5
Input Voltage (V)
5
5.5
6
100
90
80
IQ_NoSW (uA)
70
60
50
40
30
20
10
0
-40
IQ_NoSW vs. Temperature
IQ_NoSW (uA)
-20
0
20
40
60
Temperature (°C)
80
100
Frequency vs. Input Voltage
1
0.95
Frequency (MHz)
0.9
0.85
0.8
0.75
0.7
2
2.5
3
3.5
4
4.5
Input Voltage (V)
5
5.5
6
Frequency (MHz)
1.1
1.05
1
0.95
0.9
0.85
0.8
0.75
0.7
-40
Frequency vs. Temperature
-20
0
20
40
60
Temperature (°C)
80
100
Ver: 1.1
Nov 17, 2005
TEL: 886-3-5788833
http://www.gmt.com.tw
5
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