Ver: 1.3
Nov 13, 2006 TEL: 886-3-5788833
http://www.gmt.com.tw
1
G5121
Global Mixed-mode Technology Inc.
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 and TSOT-23-6 Package
Applications
White LED Backlight Display for PDA
Pocket PC
Smart Phones
Handheld Devices
Cellular Phones
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 and
TSOT-23-6 package.
Ordering Information
ORDER
NUMBER MARKING TEMP.
RANGE PACKAGE
(Pb free)
G5121TB1U 5121x -40°C ~ +85°C SOT-23-6
G5121TP1U 5121x -40°C ~ +85°C TSOT-23-6
Note:TB: SOT23-6 TP: TSOT-23-6
1: Bonding Code
U: Tape & Reel
Pin Configuration
Typical Application Circuit
VCC
SHDN
SOT-23-6/TSOT-23-6
6
4
1
SW
2
3
GND
FB
5OVP
VCC SW
SHDN FB
GND
G5121
L1
VIN
2.7V to 4. 2V
D1
OVP
5 LEDs
PW M Dimming
Waveform RS
C1
4.7µF/6.3V
4.7µH
C2
1µF/25V
C1:TAIYO YUDEN, JMK212BJ475KD
C2:TAIYO YUDEN, TMK316BJ105KD
G5121
VCC
SHDN
SOT-23-6/TSOT-23-6
6
4
1
SW
2
3
GND
FB
5OVP
VCC SW
SHDN FB
GND
G5121
L1
VIN
2.7V to 4. 2V
D1
OVP
5 LEDs
PW M Dimming
Waveform RS
C1
4.7µF/6.3V
4.7µH
C2
1µF/25V
C1:TAIYO YUDEN, JMK212BJ475KD
C2:TAIYO YUDEN, TMK316BJ105KD
G5121
Ver: 1.3
Nov 13, 2006 TEL: 886-3-5788833
http://www.gmt.com.tw
2
G5121
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
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
(VCC=VSHDN =3.6V, TA=25°C)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Input Voltage Range 2.5 --- 6 V
Input Voltage UVLO 1.7 2.0 2.3 V
Over Voltage Protection Threshold trigger 18.5 19.5 21 V
Over Voltage Protection Threshold release 13.5 15 16.5 V
OVP Pin Input Current Vovp = 16V --- 40 60 µA
VFB = 0.3V (no switching) --- 80 120 µA
VFB = 0.2V (switching) --- --- 2 mA
Quiescent Current VSHDN = 0V --- 0.1 1 µA
Initial Accuracy 244 254 264 mV
FB Comparator Trip Point Temperature Coefficient --- 100 --- ppm/°C
Switching Frequency VFB = 0.2V 0.8 1.0 1.2 MHz
Maximum Duty 85 --- --- %
Switch RDS(ON) I
SW = 150mA --- 0.7 1.0 Ω
Switch Leakage Current VSW = 20V --- 0.1 10 µA
Switch Current Limit 500 600 700 mA
Soft Start Time --- 120 --- µs
SHDN Pin Voltage High 2
--- --- V
SHDN Pin Voltage Low --- --- 0.8 V
Ver: 1.3
Nov 13, 2006 TEL: 886-3-5788833
http://www.gmt.com.tw
3
G5121
Global Mixed-mode Technology Inc.
Typical Performance Characteristics
(VCC= +3.6V, VSHDN = +3.6V, L=4.7µH, TA=25°C, unless otherwise noted.)
Stability for Driving 5 WLEDs Sta bility for Driving 4 W LEDs
Stability for Driving 3 WLEDs Sta bility for Driving 2 W LEDs
In rush Curren t for Drivi ng 5 WLEDs Inrush Current for Driving 4 WLEDs
Ver: 1.3
Nov 13, 2006 TEL: 886-3-5788833
http://www.gmt.com.tw
4
G5121
Global Mixed-mode Technology Inc.
Typical Performance Characteristics (continued)
10
20
30
40
50
60
70
80
90
0 5 10 15 20 25
Load Current (mA)
Ef ficiency (%)
5LEDs, CO=1µF
VIN=4.2V
VIN=2.7V VIN=3.6V
10
20
30
40
50
60
70
80
90
0 5 10 15 20 25
Load Current (mA)
Ef ficiency (%)
VIN=4.2V
VIN=3.6V
VIN=2.7V
4LEDs, CO=1µF
Effi ciency vs. Load Current Effi ciency vs. Load Current
In rush Curre nt for Dri vin g 3 W LEDs Inrush Curre nt for Driving 2 WLEDs
OV P Waveform Dimm i ng Control for Driving 4 WLEDs
Ver: 1.3
Nov 13, 2006 TEL: 886-3-5788833
http://www.gmt.com.tw
5
G5121
Global Mixed-mode Technology Inc.
Typical Performance Characteristics (continued)
10
20
30
40
50
60
70
80
90
0 5 10 15 20 25
Load Current (mA)
Efficiency (% )
VIN=3.6V
3LEDs, CO=1µF
VIN=4.2V
VIN=2.7V
10
20
30
40
50
60
70
80
90
0 5 10 15 20 25
Load Current (mA)
Effici ency (%)
VIN=4.2V
VIN=3.6VVIN=2.7V
2LEDs, CO=1µF
0
10
20
30
40
50
60
70
80
90
100
110
120
130
22.533.544.555.56
Input Voltage (V)
IQ_NoSW (µA)
0
10
20
30
40
50
60
70
80
90
100
-40-200 20406080100
Temperature (°C)
IQ_NoSW (µA)
0.7
0.75
0.8
0.85
0.9
0.95
1
22.533.544.555.56
Input Voltage (V)
Frequency (MHz)
0.7
0.75
0.8
0.85
0.9
0.95
1
1.05
1.1
-40-20020406080100
Temperature (°C)
Frequency (MHz)
Efficiency vs. L oad Curr en t Efficiency vs. L oad Curr en t
IQ_NoSW vs. Input Voltage IQ_NoSW vs. Temperature
Fre quency vs. I nput Volta ge Fre quency vs. Tem perature
Ver: 1.3
Nov 13, 2006 TEL: 886-3-5788833
http://www.gmt.com.tw
6
G5121
Global Mixed-mode Technology Inc.
Typical Performance Characteristics (continued)
17
17.5
18
18.5
19
19.5
20
20.5
21
2 2.5 3 3.5 4 4.5 5 5.5 6
Input Voltage (V)
OVP Trigger Threshold (V)
17
17.5
18
18.5
19
19.5
20
20.5
21
-40-20020406080100
Temperature (°C)
OVP Trigger Threshold (V)
13
13.5
14
14.5
15
15.5
16
16.5
17
2 2.5 3 3.5 4 4.5 5 5.5 6
Input Voltage (V)
OVP Release Threshold (V)
13
13.5
14
14.5
15
15.5
16
16.5
17
-40-20020406080100
Temperature (°C)
OVP Release Threshold (V)
0
10
20
30
40
50
60
22.533.544.555.56
Input Voltage (V)
O VP Pi n I nput Current (µA)
0
10
20
30
40
50
60
-40 -20 0 20 40 60 80 100
Temperature (°C)
O VP Pi n I nput Current (µA)
OVP Tri gger Threshold vs. I nput Vol tage OVP T rigger Threshold vs. Tem pera ture
OVP Re l ease Thre shold vs. I nput Volta ge OVP Re l ease Thre shold vs. Tem perature
OVP Pi n I np ut Curre nt vs. I nput Vol ta ge OVP Pin Input Current vs. Temperature
Ver: 1.3
Nov 13, 2006 TEL: 886-3-5788833
http://www.gmt.com.tw
7
G5121
Global Mixed-mode Technology Inc.
Recommended Minimum Footprint
Block Diagram
+
VREF
SW
FB
0.254V
GND
CONTROL
DRIVER
+
OC
OVP
SHDN
RSQ
1MHz
OSCILLATOR
VCC
COMPENSATION
COMPARATOR
A2
+
A1
RAMP
GENERATOR
M1
+
VREF
SW
FB
0.254V
GND
CONTROL
DRIVER
+
OC
OVP
SHDN
RSQ
1MHz
OSCILLATOR
VCC
COMPENSATION
COMPARATOR
A2
+
A1
RAMP
GENERATOR
M1
SOT-23-6/TSOT-23-6SOT-23-6/TSOT-23-6
Ver: 1.3
Nov 13, 2006 TEL: 886-3-5788833
http://www.gmt.com.tw
8
G5121
Global Mixed-mode Technology Inc.
Pin Description
PIN NAME FUNCTION
1 SW
S
witch Pin. The drain of the internal NMOS power switch. Connect this pin to inductor.
2 GND
Ground Pin.
3 FB
Feedback Pin. Connect current setting resistor Rs from this pin to ground. The LED current is set a
s
0
.254V/ Rs.
4 SHDN
A
ctive Low Shutdown Pin.
5 OVP
Over Voltage Protection Sense Pin.
6 VCC
Input Supply Pin. Bypass this pin with a capacitor as close to the device as possible.
Function Description
Normal Operation
The G5121 uses a constant frequency control scheme
to provide excellent line and load regulation. Operation
can be best understood by referring to the block dia-
gram. At the start of each oscillator cycle, the SR latch
is set, which turns on the power switch M1. An artificial
ramp is generated to the positive terminal of the PWM
comparator A2. When this voltage exceeds the level at
the negative input of A2, the SR latch is reset turning
off the power switch. The level at the negative input of
A2 is set by the error amplifier A1, and is simply an
amplified version of the difference between the feed-
back voltage and the reference voltage of 0.254V. In
this manner, the error amplifier sets the correct peak
current level to keep the output in regulation. If the
error amplifier’s output increases, more current is de-
livered to the output, if it decreases, less current is
delivered.
Over Voltage Protection
Over voltage protection function is designed to prevent
the damage of internal NMOS switch in case the in-
creased impedance of the LED load (include the LED
opened). Once the device detects over voltage (typical
19.5V) at the output, the internal NMOS switch is kept
off until the output voltage drops below 15V.
Application Information
Inductor Selection
A 4.7µF inductor is recommended for G5121 applica-
tions. Small size and high efficiency are the major
concerns for most G5121 applications. Inductor with
low core losses and small DCR (cooper wire resis-
tance) at 1MHz are good choice for G5121 applica-
tions.
Since the G5121 is designed to operate in discontinu-
ous mode, the inductor current reaches zero during
discharge phase. After the inductor current reaches
zero, the switch pin exhibits ringing due to the LC tank
circuit formed by the inductor in combination with
switch and diode capacitance. This ringing is not
harmful; far less spectral energy is contained in the
ringing than in the switch transitions. The ringing can
be damped by application of a 300Ω resistor across
the inductor, although this will degrade efficiency.
Capacitor Selection
The small size of ceramic capacitors makes them suit-
able for G5121 applications. X5R and X7R types are
recommended because they retain their capacitance
over wider voltage and temperature ranges than other
types such as Y5V or Z5U. A minimum 1µF capacitor
for output is required for most applications. Larger in-
put/output capacitor minimizes input/output ripple.
Diode Selection
Schottky diodes, with their low forward voltage drop
and fast reverse recovery, are the ideal choices for
G5121 applications. The forward voltage drop of a
Schottky diode represents the conduction losses in the
diode, while the diode capacitance (CT or CD) repre-
sents the switching losses. For diode selection, both
forward voltage drop and diode capacitance need to
be considered. Schottky diodes with higher current
ratings usually have lower forward voltage drop and
larger diode capacitance, which can cause significant
switching losses at the 1MHz switching frequency of
the G5121. A Schottky diode rated at 500mA is suffi-
cient for most G5121 applications.
Ver: 1.3
Nov 13, 2006 TEL: 886-3-5788833
http://www.gmt.com.tw
9
G5121
Global Mixed-mode Technology Inc.
Package Information
SOT-23-6 (TB) Package
Note:
1. Package body sizes exclude mold flash protrusions or gate burrs
2. Tolerance ±0.1000 mm (4mil) unless otherwise specified
3. Coplanarity: 0.1000mm
4. Dimension L is measured in gage plane
DIMENSION IN MM DIMENSION IN INCH
SYMBOL MIN. NOM. MAX. MIN. NOM. MAX.
A 1.00 1.10 1.30 0.039 0.043 0.051
A1 0.00 ----- 0.10 0.000 ----- 0.004
A2 0.70 0.80 0.90 0.028 0.031 0.035
b 0.35 0.40 0.50 0.014 0.016 0.020
C 0.10 0.15 0.25 0.004 0.006 0.010
D 2.70 2.90 3.10 0.106 0.114 0.122
E 1.40 1.60 1.80 0.055 0.063 0.071
e ----- 1.90(TYP) ----- ----- 0.075(TYP) -----
H 2.60 2.80 3.00 0.102 0.110 0.118
L 0.37 ------ ----- 0.015 ----- -----
θ1 1º 5º 9º 1º 5º 9º
E
D
H
θ1
L
C
b
A2
A1
A
e
e1
E
D
H
θ1
L
C
b
A2
A1
A
e
e1
Ver: 1.3
Nov 13, 2006 TEL: 886-3-5788833
http://www.gmt.com.tw
10
G5121
Global Mixed-mode Technology Inc.
TSOT-23-6 (TP) Package
Note:
1. Dimension D does not include mold flash, protrusions or tate burrs. Mold flash, protrusions or gate burrs shall not exceed
0.1mm PER end. Dimension E1 does not include interlead flash or protrusion. Interlead flash or protrusion shall not ex-
ceed 0.15mm PER side.
2. The package top may be smaller than the package bottom. Dimensions D and E1 are determined at the outermost ex-
tremes of the plastic body exclusive of mold flash, tie bar burrs, gate burrs and interlead flash, but including any mis-
match between the top and bottom of the plastic body.
DIMENSION IN MM DIMENSION IN INCH
SYMBOL MIN. NOM. MAX. MIN. NOM. MAX.
A 0.75 ----- 1.00 0.030 ----- 0.039
A1 0.00 ----- 0.10 0.000 ----- 0.004
A2 0.70 0.75 0.80 0.028 0.030 0.031
b 0.35 ----- 0.51 0.014 ----- 0.020
C 0.10 ----- 0.25 0.004 ----- 0.010
D 2.80 2.90 3.00 0.110 0.114 0.118
E 2.60 2.80 3.00 0.102 0.110 0.118
E1 1.50 1.60 1.70 0.059 0.063 0.067
e 0.95 BSC 0.0374 BSC
e1 1.90 BSC 0.0748 BSC
L 0.37 ----- ----- 0.015 ----- -----
y ----- ----- 0.10 ----- 0.004
θ1 0° ----- 8° 0° ----- 8°
Taping Specification
PACKAGE Q’TY/REEL
SOT-23-6 3,000 ea
TSOT-23-6 3,000 ea
GMT Inc. does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and GMT Inc. reserves the right at any time without notice to change said circuitry and specifications.
E1
D
E
θ1
L
C
b
A2 A
e1
e
A1
y
E1
D
E
θ1
L
C
b
A2 A
e1
e
A1
y
Feed Direction
SOT- 23-6 / TSOT-23-6 Package Orientation
Feed Direction
SOT- 23-6 / TSOT-23-6 Package Orientation