G5121 Global Mixed-mode Technology Inc. Fixed Frequency White LED Step-Up Converter Features General Description Inherently Matched LED Current High Efficiency: 87% Typical Drives Up to Five LEDs from 2.5V Supply 24V Internal Power Switch Fast 850kHz Switching Frequency Uses Tiny 1mm Tall Inductors Requires Only 1µF Output Capacitors 20V Over Voltage Protection SOT-23-6 Package 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 850kHz, allowing the use of tiny external components. A low 0.25V 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. Applications The G5121 is available in low profile SOT-23-6 package. White LED Backlight Display for PDA Pocket PC Smart Phones Handheld Devices Cellular Phones Ordering Information ORDER NUMBER MARKING TEMP. RANGE PACKAGE (Pb free) G5121TB1U 5121x -40°C ~ +85°C SOT-23-6 Note: TB : SOT23-6 U: Tape & Reel Pin Configuration SW GND FB 1 Typical Application Circuit 6 VCC 4.7µF VCC 2 G5121 SW C2 1µF/25V 5 LEDs OVP 5 4 3 D1 L1 VIN 2.7V to 4.2V C1 4.7µF/6.3V OVP SHDN PWM Dimming Waveform G5121 SHDN GND FB RS SOT-23-6 TEL: 886-3-5788833 http://www.gmt.com.tw Ver: 0.1 Preliminary Nov 16, 2004 1 G5121 Global Mixed-mode Technology Inc. Absolute Maximum Ratings Junction Temperature......................…...................125°C Storage Temperature……....………….….-65°C to 150°C Reflow Temperature (soldering, 10sec)………….260°C 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. Electrical Characteristics (VCC=V SHDN =3.6V, TA=25°C) PARAMETER CONDITIONS Input Voltage Range Input Voltage UVLO MIN TYP MAX UNITS 2.5 --- 5.5 V 1.7 2.0 2.3 V Over Voltage Protection Threshold trigger --- 20 --- V Over Voltage Protection Threshold release --- 16 --- V OVP Pin Input Current Vovp = 16V --- 40 60 µA VFB = 0.3V (no switching) --- 80 120 µA VFB = 0.2V (switching) V SHDN = 0V --- --- 2 mA --- 0.1 1 µA 237 250 263 mV --- 100 --- ppm/°C kHz Quiescent Current FB Comparator Trip Point Switching Frequency Initial Accuracy Temperature Coefficient 700 850 1000 Maximum Duty VFB = 0.2V 85 --- --- % Minimum Duty --- --- 20 % Switch RDS(ON) ISW = 150mA --- 0.7 1.0 Ω Switch Leakage Current VSW = 20V --- 0.1 10 µA Switch Current Limit --- 700 --- mA Switch Current Limit (startup) --- 250 --- mA SHDN Pin Voltage High 2 --- --- V SHDN Pin Voltage Low --- --- 0.8 V TEL: 886-3-5788833 http://www.gmt.com.tw Ver: 0.1 Preliminary Nov 16, 2004 2 G5121 Global Mixed-mode Technology Inc. Block Diagram FB SW OVP COMPENSATION COMPARATOR A1 + A2 + DRIVER R S CONTROL Q M1 0.25V VREF RAMP GENERATOR OC + 850kHz OSCILLATOR VCC SHDN GND TEL: 886-3-5788833 http://www.gmt.com.tw Ver: 0.1 Preliminary Nov 16, 2004 3 Global Mixed-mode Technology Inc. G5121 Pin Description PIN NAME 1 2 SW GND FUNCTION 3 FB 4 SHDN Ground Pin. Feedback Pin. Connect current setting resistor Rs from this pin to ground. The LED current is set as 0.25V/ Rs. Active Low Shutdown Pin. 5 6 OVP VCC Over Voltage Protection Sense Pin. Input Supply Pin. Bypass this pin with a capacitor as close to the device as possible. Switch Pin. The drain of the internal NMOS power switch. Connect this pin to inductor. Function Description 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. 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 0.25V. 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. 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. 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 20V) at the output, the internal NMOS switch is kept off until the output voltage drops below 16V. 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 850kHz switching frequency of the G5121. A Schottky diode rated at 500mA is sufficient for most G5121 applications. 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 850kHz are good choice for G5121 applications. TEL: 886-3-5788833 http://www.gmt.com.tw Ver: 0.1 Preliminary Nov 16, 2004 4 G5121 Global Mixed-mode Technology Inc. Package Information C D L E H θ1 e1 e A A2 A1 b Note: 1. Package body sizes exclude mold flash protrusions or gate burrs 2. 3. Tolerance ±0.1000 mm (4mil) unless otherwise specified 4. Coplanarity: 0.1000mm 5. Dimension L is measured in gage plane SYMBOL MIN DIMENSIONS IN MILLIMETER NOM MAX A A1 A2 b C D E 1.00 0.00 0.70 0.35 0.10 2.70 1.40 1.10 ----0.80 0.40 0.15 2.90 1.60 1.30 0.10 0.90 0.50 0.25 3.10 1.80 e e1 --------- 1.90(TYP) 0.95 --------- H L θ1 2.60 0.37 2.80 ------ 3.00 ----- 1º 5º 9º Taping Specification PACKAGE Q’TY/REEL SOT-23-6 3,000 ea 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. TEL: 886-3-5788833 http://www.gmt.com.tw Ver: 0.1 Preliminary Nov 16, 2004 5