Page 1
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
Applications
White LED Backlight Display for PDA
Pocket PC
General Description
The G5121 is a step-up DC/DC converter specifically
designed to drive up to 5 series white LEDs with constant 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 external components. A low 0.254V feedback voltage
minimizes power loss in the current setting resistor for
high efficiency. The OVP pin monitors the output voltage and turns off the converter whenever the LEDs
are open.
The G5121 is available in low profile SOT-23-6 package.
Smart Phones
Handheld Devices
Cellular Phones
Ordering Information
ORDER
NUMBER
MARKING
TEMP.
RANGE
G5121TB1U 5121x -40°C ~ +85°C SOT-23-6
Note: TB : SOT23-6
U: Tape & Reel
Pin Configuration Typical Application Circuit
PACKAGE
(Pb free)
1
1
1
SW
SW
SW
2
2
2
GND
GND
GND
3
3
3
FB
FB
FB
Ver: 1.1
Nov 17, 2005
G5121
G5121
G5121
SOT-23-6
SOT-23-6
SOT-23-6
6
6
6
5
5
5
4
4
4
VCC
VCC
VCC
OVP
OVP
OVP
SHDN
SHDN
SHDN
V
V
V
IN
IN
2.7V to 4.2V
2.7V to 4.2V
2.7V to 4.2V
PWM Dimming
PWM Dimming
PWM Dimming
Waveform
Waveform
Waveform
C1:TAIYO YUDEN, JMK212BJ475KD
C1:TAIYO YUDEN, JMK212BJ475KD
C2:TAIYO YUDEN, TMK316BJ105KD
C2:TAIYO YUDEN, TMK316BJ105KD
IN
4.7µF/6.3V
4.7µF/6.3V
4.7µF/6.3V
C1
C1
C1
1
VCC
VCC
VCC
G5121
G5121
G5121
SHDN
SHDN
SHDN
L1
L1
L1
4.7µH
4.7µH
4.7µH
GND
GND
GND
SW
SW
SW
OVP
OVP
OVP
FB
FB
FB
D1
D1
D1
C2
C2
C2
1µF/25V
1µF/25V
1µF/25V
R
R
R
S
S
S
TEL: 886-3-5788833
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5 LEDs
5 LEDs
5 LEDs
Page 2
Global Mixed-mode Technology Inc.
G5121
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
Stress beyond those listed under “Absolute Maximum Rating” may cause permanent damage to the device.
Junction Temperature......................….................125°C
Storage Temperature……....……..….….-65°C to 150°C
Reflow Temperature (soldering, 10sec)……...…260°C
ESD Rating (Human Body Model)………….….……2kV
Electrical Characteristics
(VCC=VSHDN =3.6V, TA=25°C)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Input Voltage Range 2.5
Input Voltage UVLO 1.7 2.0 2.3 V
Over Voltage Protection Threshold trigger
Over Voltage Protection Threshold release
OVP Pin Input Current V
Quiescent Current
FB Comparator Trip Point
Switching Frequency V
Maximum Duty 85
Switch R
Switch Leakage Current VSW = 20V
Switch Current Limit 500 600 700 mA
Soft Start Time
SHDN
SHDN Pin Voltage Low
I
DS(ON)
Pin Voltage High
= 16V
ovp
V
= 0.3V (no switching)
FB
V
= 0.2V (switching)
FB
V SHDN = 0V
Initial Accuracy 244 254 264 mV
Temperature Coefficient
= 0.2V 0.8 1.0 1.2 MHz
FB
= 150mA
SW
2
18.5
13.5
---
---
--- ---
---
---
---
---
---
--- ---
---
19.5 21 V
15
40 60 µA
80 120 µA
0.1 1 µA
100
--- ---
0.7 1.0
0.1 10 µA
120
--- ---
6 V
16.5
2 mA
---
---
0.8 V
V
ppm/°C
%
Ω
µs
V
Ver: 1.1
Nov 17, 2005
2
TEL: 886-3-5788833
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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
G5121
Stability for Driving 4 WLEDs
Stability for Driving 3 WLEDs
Inrush Current for Driving 5 WLEDs
Stability for Driving 2 WLEDs
Inrush Current for Driving 4 WLEDs
Ver: 1.1
Nov 17, 2005
3
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Global Mixed-mode Technology Inc.
Typical Performance Characteristics (continued)
Inrush Current for Driving 3 WLEDs
G5121
Inrush Current for Driving 2 WLEDs
OVP Waveform
Efficie n cy vs. Load Cu rr ent Efficie n cy vs. Load Cu rr ent
90
80
70
60
50
40
Efficiency (%)
30
20
10
0 5 10 15 20 25
VIN=2.7V
Load Current (mA)
VIN=3.6V
VIN=4.2V
5LEDs, CO=1µF
Dimming Control for Driving 4 WLEDs
90
80
70
60
50
40
Efficiency (%)
30
20
10
0 5 10 15 20 25
VIN=2.7V
VIN=3.6V
4LE Ds, CO=1µF
Load Current (mA)
VIN=4.2V
Ver: 1.1
Nov 17, 2005
4
TEL: 886-3-5788833
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Global Mixed-mode Technology Inc.
Typical Performance Characteristics (continued)
G5121
90
80
70
60
50
40
Efficiency (%)
30
20
10
0 5 10 15 20 25
VIN=2.7V
Load Current (mA)
VIN=3.6V
VIN=4.2V
3LEDs, CO=1µF
IQ_NoSW vs. Input Voltage IQ_NoSW vs. Temperature
130
120
110
100
90
80
70
60
50
IQ_NoSW (uA)
40
30
20
10
0
Efficiency vs. Load Current Efficiency vs. Load Current
22.533.544.555.56
Input Voltage (V)
90
80
70
60
50
40
Efficiency (%)
30
20
10
0 5 10 15 20 25
100
90
80
70
60
50
40
IQ_NoSW (uA)
30
20
10
0
-40 -20 0 20 40 60 80 100
VIN=2.7V
Load Current (mA)
Temperature (°C)
VIN=3.6V
2LEDs, CO=1µF
VIN=4.2V
1
0.95
0.9
0.85
0.8
Frequency (MHz)
0.75
0.7
2 2.5 3 3.5 4 4.5 5 5.5 6
Ver: 1.1
Nov 17, 2005
Frequency vs. Input Voltage
Input Voltage (V)
5
Frequency vs. Temperature
1.1
1.05
1
0.95
0.9
0.85
Frequency (MHz)
0.8
0.75
0.7
-40 -20 0 20 40 60 80 100
Temperature (°C)
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Global Mixed-mode Technology Inc.
Typical Performance Characteristics (continued)
G5121
OVP Trigger Threshold vs. Input Voltage
21
20.5
20
19.5
19
18.5
18
OVP Trigger Threshold (V)
17.5
17
2 2.5 3 3.5 4 4.5 5 5.5 6
Input Voltage (V)
OVP Release Threshold vs. Input Voltage
17
16.5
16
15.5
15
14.5
14
OVP Release Threshold (V)
13.5
13
2 2.5 3 3.5 4 4.5 5 5.5 6
Input Voltage (V)
OVP Trigger Threshold vs. Temperature
21
20.5
20
19.5
19
18.5
18
OVP Trigger Threshold (V)
17.5
17
-40-200 20406080100
Temperature (°C)
OVP Release Threshold vs. Temperature
17
16.5
16
15.5
15
14.5
14
OVP Release Threshold (V)
13.5
13
-40-200 20406080100
Temperature (°C)
OVP Pin Input Current vs. Input Voltage
60
50
40
30
20
OVP Pin Input Current (uA)
10
0
22.533.544.555.56
Ver: 1.1
Nov 17, 2005
Input Voltage (V)
6
OVP Pin Input Current vs. Temperature
60
50
40
30
20
OVP Pin Input Current (uA)
10
0
-40-200 20406080100
Temperature (°C)
TEL: 886-3-5788833
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Global Mixed-mode Technology Inc.
Recommended Minimum Footprint
SOT-23-6
G5121
Block Diagram
FB
FB
0.254V
0.254V
VREF
VREF
COMPENSATION
COMPENSATION
A1
A1
+
+
RAMP
RAMP
GENERATOR
GENERATOR
OSCILLATOR
OSCILLATOR
COMPARATOR
COMPARATOR
1MHz
1MHz
SW
OVP
OVP
DRIVER
DRIVER
CONTROL
Q
A2
A2
+
+
Q
R
R
S
S
CONTROL
OC
OC
+
+
SW
M1
M1
Ver: 1.1
Nov 17, 2005
VCC
VCC
7
GND
SHDN
SHDN
GND
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Page 8
S
s
0
A
Global Mixed-mode Technology Inc.
Pin Description
PIN NAME FUNCTION
1 SW
2 GND
3 FB
4
5 OVP
6 VCC
SHDN
witch Pin. The drain of the internal NMOS power switch. Connect this pin to inductor.
Ground Pin.
Feedback Pin. Connect current setting resistor Rs from this pin to ground. The LED current is set a
.254V/ Rs.
ctive Low Shutdown Pin.
Over Voltage Protection Sense Pin.
Input Supply Pin. Bypass this pin with a capacitor as close to the device as possible.
G5121
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 diagram. 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 feedback 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 delivered 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 increased 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 applications. Small size and high efficiency are the major
concerns for most G5121 applications. Inductor with
low core losses and small DCR (cooper wire resistance) at 1MHz are good choice for G5121 applications.
Since the G5121 is designed to operate in discontinuous 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 suitable 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 input/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 (C
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 sufficient for most G5121 applications.
or CD) repre-
T
Ver: 1.1
Nov 17, 2005
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Page 9
Global Mixed-mode Technology Inc.
Package Information
A2
A2
G5121
C
D
D
H
H
E
E
e1
e1
e
e
A
A
A1
A1
b
b
C
L
L
θ1
θ1
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
SYMBOL
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
MIN. NOM. MAX. MIN. NOM. MAX.
1º 5º 9º 1º 5º 9º
DIMENSION IN MM DIMENSION IN INCH
Taping Specification
PACKAGE Q’TY/REEL
SOT-23-6 3,000 ea
Feed Direction
SOT- 23-6 Package Orientation
SOT- 23-6 Package Orientation
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.
Feed Direction
Ver: 1.1
Nov 17, 2005
9
TEL: 886-3-5788833
http://www.gmt.com.tw
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