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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 1F 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 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.
Applications
White LED Backlight Display for PDA Pocket PC Smart Phones Handheld Devices Cellular Phones
Ordering Information
ORDER NUMBER
G5121TB1U
MARKING
5121x
TEMP. RANGE
-40C ~ +85C
PACKAGE (Pb free)
SOT-23-6
Note: TB : SOT23-6
U: Tape & Reel
Pin Configuration
Typical Application Circuit
L1 VIN 2.7V to 4.2V
D1
SW
1
6
VCC
VCC
4.7H SW OVP C2 1F/25V 5 LEDs
GND
2
G5121
5
OVP
C1 4.7F/6.3V PWM Dimming Waveform
G5121
SHDN GND FB RS
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
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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.........................-40C to 85C
G5121
Junction Temperature..........................................125C Storage Temperature..........................-65C to 150C Reflow Temperature (soldering, 10sec)............260C ESD Rating (Human Body Model).......................2kV
Stress beyond those listed under "Absolute Maximum Rating" may cause permanent damage to the device.
Electrical Characteristics
(VCC=V SHDN =3.6V, TA=25C) PARAMETER
Input Voltage Range Input Voltage UVLO Over Voltage Protection Threshold Over Voltage Protection Threshold OVP Pin Input Current Quiescent Current trigger release Vovp = 16V VFB = 0.3V (no switching) VFB = 0.2V (switching) V SHDN = 0V Initial Accuracy Temperature Coefficient VFB = 0.2V ISW = 150mA VSW = 20V
CONDITIONS
MIN
2.5 1.7
18.5 13.5 ---------
TYP
---
MAX
6 2.3 21
16.5
UNITS
V V V V A A mA A mV ppm/C MHz % A mA s 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 RDS(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
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Global Mixed-mode Technology Inc.
Typical Performance Characteristics
(VCC= +3.6V, V SHDN = +3.6V, L=4.7H, TA=25C, 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
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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
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, CO=1F 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, CO=1F
20
25
Ver: 1.1 Nov 17, 2005
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Global Mixed-mode Technology Inc.
Typical Performance Characteristics (continued)
Efficiency vs. Load Current
90 80 VIN=2.7V 70 Efficiency (%) 60 50 40 30 20 10 0 5 10 15 Load Current (mA) 20 25 3LEDs, CO=1F VIN=3.6V VIN=4.2V Efficiency (%) 90 80 VIN=2.7V 70 60 50 40 30 20 10 0 5 10 15 Load Current (mA)
G5121
Efficiency vs. Load Current
VIN=3.6V VIN=4.2V
2LEDs, CO=1F
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
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Global Mixed-mode Technology Inc.
Typical Performance Characteristics (continued)
OVP Trigger Threshold vs. Input Voltage
21 20.5 20 19.5 19 18.5 18 17.5 17 2 2.5 3 3.5 4 4.5 Input Voltage (V) 5 5.5 6 OVP Trigger Threshold (V) OVP Trigger Threshold (V) 21 20.5 20 19.5 19 18.5 18 17.5 17 -40 -20 0 20 40
G5121
OVP Trigger Threshold vs. Temperature
60
80
100
Temperature (C)
OVP Release Threshold vs. Input Voltage
17 16.5 OVP Release Threshold (V) 16 15.5 15 14.5 14 13.5 13 2 2.5 3 3.5 4 4.5 Input Voltage (V) 5 5.5 6 OVP Release Threshold (V) 17 16.5 16 15.5 15 14.5 14 13.5 13
OVP Release Threshold vs. Temperature
-40
-20
0
20 40 60 Temperature (C)
80
100
OVP Pin Input Current vs. Input Voltage
60 50 40 30 20 10 0 2 2.5 3 3.5 4 4.5 Input Voltage (V) 5 5.5 6 60 50 40 30 20 10 0
OVP Pin Input Current vs. Temperature
OVP Pin Input Current (uA)
OVP Pin Input Current (uA)
-40
-20
0
20 40 60 Temperature (C)
80
100
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Global Mixed-mode Technology Inc.
Recommended Minimum Footprint
SOT-23-6
G5121
Block Diagram
FB
OVP
SW
COMPENSATION
COMPARATOR A1 + A2 + R S Q CONTROL
DRIVER M1
0.254V VREF RAMP GENERATOR
+
OC
1MHz OSCILLATOR
VCC
SHDN
GND
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Global Mixed-mode Technology Inc.
Pin Description
PIN
1 2 3 4 5 6
G5121
NAME
SW GND FB
SHDN
FUNCTION
Switch 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 as 0.254V/ Rs. Active Low Shutdown Pin. Over Voltage Protection Sense Pin. Input Supply Pin. Bypass this pin with a capacitor as close to the device as possible.
OVP VCC
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.
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 300 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 1F 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 (CT or CD) represents 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.
Application Information
Inductor Selection A 4.7F 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.
Ver: 1.1 Nov 17, 2005
TEL: 886-3-5788833 http://www.gmt.com.tw
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Global Mixed-mode Technology Inc.
Package Information
G5121
C L
D
E
H
e1 e
1
A2
A A1 b
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 A1 A2 b C D E e H L 1
MIN.
1.00 0.00 0.70 0.35 0.10 2.70 1.40 ----2.60 0.37 1
DIMENSION IN MM NOM.
1.10 ----0.80 0.40 0.15 2.90 1.60 1.90(TYP) 2.80 -----5
MAX.
1.30 0.10 0.90 0.50 0.25 3.10 1.80 ----3.00 ----9
MIN.
0.039 0.000 0.028 0.014 0.004 0.106 0.055 ----0.102 0.015 1
DIMENSION IN INCH NOM.
0.043 ----0.031 0.016 0.006 0.114 0.063 0.075(TYP) 0.110 ----5
MAX.
0.051 0.004 0.035 0.020 0.010 0.122 0.071 ----0.118 ----9
Taping Specification
PACKAGE
SOT-23-6
Feed Direction 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.
Q'TY/REEL
3,000 ea
Ver: 1.1 Nov 17, 2005
TEL: 886-3-5788833 http://www.gmt.com.tw
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