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EUP2518
White LED Step-Up Converter In TSOT-23 Package
DESCRIPTION
The EUP2518 is a constant current step-up converter specifically designed to drive white LEDs. The Step-up converter topology allows series connection of the white LEDs so the LED currents are identical for uniform brightness. The EUP2518 switches at 1.1MHz, allowing the use of tiny external components. The output capacitor can be as small as 0.22uF, saving space and cost versus alternative solutions. A low 104mV feedback voltage minimizes power loss in the current setting resistor for better efficiency. EUP2518 is enhanced with Soft-Start function and that could significantly reduce noise induced by capacitor. The EUP2518 is available in low profile TSOT23-6 package.
FEATURES
2.6V to 5.5V Input Range 27V Output with Over Voltage Protection High Efficiency :87 % Typical Internal Soft-Start PWM Dimming Control Internal High Power 30V MOSFET Switch Fast 1.1MHz Switching Frequency Small, Low-Profile Inductors and Capacitors TSOT23-6 Package RoHS Compliant and 100% Lead (Pb)-Free
APPLICATIONS
Mobile Phone Digital Still Camera PDAs, Handheld Computers MP3 Players GPS Receivers
Typical Application Circuit
Figure 1. White LED Application
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Pin Configurations
Package Type Pin Configurations
TSOT23-6
Pin Description
PIN LX GND FB EN OUT IN TSOT23-6 1 2 3 4 5 6 DESCRIPTION Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to reduce EMI. Common Ground Feedback Pin. Reference voltage is 104mV. Connect cathode of lowest LED and resistor here. Calculate resistor value according to the formula: RFB=104/ILED Chip Enable Pin. Connect to 1.4V or higher to enable device, 0.3V or less to disable device. Overvoltage Sense. When VOUT is greater than 27V, the internal N-channel MOSFET turns off until VOUT drops below 25V, then the IC reenters start. Connect a 0.22uF capacitor from OUT to GND. Input Supply Voltage
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Ordering Information
Order Number EUP2518OIR1 Package Type TSOT23-6 Marking Operating Temperature Range -40 C to 85C
50
EUP2518 Lead Free Code 1: Lead Free 0: Lead Packing R: Tape & Reel Operating temperature range I: Industry Standard Package Type O: TSOT
Block Diagram
Figure 2.
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Absolute Maximum Ratings
Supply Voltage ,VIN ----------------------------------------------------------------LX,OUT ----------------------------------------------------------------------------The Other Pins ---------------------------------------------------------------------Package Thermal Resistance TSOT23-6,JA ----------------------------------------------------------------------Maximum Junction Temperature --------------------------------------------------Lead Temperature (Soldering, 10sec.) --------------------------------------------Storage Temperature Range ---------------------------------------------------------0.3V to 6V -0.3V to 30V -0.3V to 6V 220C/W 125C 260C -65C to 150C
Operating Conditions
Junction Temperature Range ------------------------------------------------------- -40C to 125C Supply Voltage , VIN----------------------------------------------------------------- 2.6V to 5.5V
Electrical Characteristics
(VIN =3.6V, VOUT=18V, COUT=0.22F, CIN=1F, RFB=5.1, TA=-40C to 85C. Unless otherwise noted. Typical values are at TA= 25C)
Symbol
Parameter
Supply Voltage
Conditions
VIN Rising VIN Falling No Switching VCC=6V, Continuous Switching VCC=6V, FB=1.3V, No Switching VCC=6V, VEN<0.3V
Min
-2.2 1.95 ----0.8 89 94 -0.4 0.3 ---
EUP2518 Typ Max.
-2.4 2.15 -0.8 115 0.1 1.1 92 104 1 0.8 0.7 0.7 -25.7 27.3 6 2.6 2.35 30 1.3 150 1 1.3 96 114 1.5 1.2 -1.4 0.1 26.5 28.1
Unit
V V V mA A A MHz % mV A V V A V
UVLO
Under Voltage Lock Out Maximum Output Voltage Supply Current Quiescent Current Shutdown current Operation Frequency Maximum Duty Cycle Feedback Voltage On resistance of MOSFET Current Limit Shutdown Voltage Enable Voltage EN Pin Pull Low Current OVP Threshold
ICC1 ICC2 ICC3 Oscillator Fosc Dmax VFB MOSFET RDS(ON) ILX VEN1 VEN2 IEN OVP
Reference Voltage
Control and Protection
Falling Rising
24.5 26.1
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Typical Operating Characteristics
Efficiency vs LED Current
91
Startup Waveforms into an Open Load
87
EFFICENCY (%)
VEN
83
VOUT
79
6 LED 3 LED 4 LED
VSW
75
5 10 15 20
LED CURRENT (mA)
Startup Waveforms
Steady State Operation(VIN=3.6V, 3 LEDs, 20mA)
VEN
VSW
VOUT VOUT
IIN
IL
1KHz 50% Duty Cycle PWM Dimming
10KHz 50% Duty Cycle PWM Dimming
VEN
VEN
VOUT
VOUT
IIN
IIN
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Application Information
LED Current Control The EUP2518 regulates the LED current by setting the current sense resistor (RFB) connecting to feedback and ground. The internal feedback reference voltage is 104mV. The LED current can be set from following equation easily.
R FB = 104mV I LED -------------------------------------(1) b. Using a DC Voltage Using a variable DC voltage to adjust the brightness is a popular method in some applications. The dimming control using a DC voltage circuit is shown in Figure 4. According to the Superposition Theorem, as the DC voltage increases, the voltage contributed to VFB increases and the voltage drop on RFB decreases, i.e. the LED current decreases. For example, if the VDC range is from 0V to 2V, the selection of resistors in Figure 4 sets dimming control of LED current from 20mA to 0mA.
In order to have an accurate LED current, precision resistors are preferred (1% is recommended). The table for RFB selection is shown below. RFB Resistor Value selection RFB () ILED (mA) 5 21 10 10.4 15 6.93 20 5.2
CAP and Inductor Selection The recommended value of inductor for 2 to 6 WLEDs applications are 10H to 47H. Small size and better efficiency are the major concerns for portable device. A 22H inductor with low DCR (Inductor resistance) is recommended to improve efficiency. To avoid inductor saturation current rating should be considered. A 1F ceramic capacitor is recommended for the input capacitance in the real system, and a larger capacitor will get smaller input voltage ripple. A 0.22uF output ceramic capacitor is sufficient for most applications. Dimming Control
a. Using a PWM Signal to EN Pin For controlling the LED brightness, the EUP2518 can perform the dimming control by applying a PWM signal to EN pin. The internal soft-start and wide range dimming frequency from 100Hz to 100KHz can insignificantly reduce audio noise when dimming. The average LED current is proportional to the PWM signal duty cycle. The magnitude of the PWM signal should be higher than the maximum enable voltage of EN pin, in order to let the dimming control perform correctly.
Figure 4. Dimming Control Using a DC Voltage
c. Using a Filtered PWM signal Another common application is using a filtered PWM signal as an adjustable DC voltage for LED dimming control. A filtered PWM signal acts as the DC voltage to regulate the output current. In this circuit, the output ripple depends on the frequency of PWM signal. For smaller output voltage ripple (<100mV), the recommended frequency of 2V PWM signal should be above 2kHz. To fix the frequency of PWM signal and change the duty cycle of PWM signal can get different output current. According to the application circuit of Figure 5, output current is from 20.5mA to 5.5mA by adjusting the PWM duty cycle from 10% to 90%.
Figure 5. Filtered PWM Signal for LED Dimming Control Figure 3. PWM Dimming Control Using the EN Pin
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Layout Considerations The input bypass capacitor C2, as shown in Figure 1, must be placed close to the IC. This will reduce copper trace resistance which effects input voltage ripple of the IC. The output capacitor, C1, should also be placed close to the IC. Any copper trace connections for the C1 capacitor can increase the series resistance, which directly effects output voltage ripple. The feedback resistors RFB should be kept close to the FB pin to minimize copper trace connections that can inject noise into the system. The ground connection for the feedback resistor network should connect directly to GND pin. Trace connections made to the inductor and schottky diode should be minimized to reduce EMI and increase overall efficiency.
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Packaging Information
TSOT23-6
SYMBOLS A A1 b D E1 e E L
MILLIMETERS MIN. MAX. 1.00 0.00 0.15 0.30 0.50 2.90 1.60 0.95 2.60 3.00 0.3 0.60
INCHES MIN. 0.000 0.012 0.114 0.063 0.037 0.102 0.012 0.118 0.024 MAX. 0.039 0.006 0.020
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