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EUP2571 White LED Step-Up Converter In Tiny SOT-23 Package
DESCRIPTION
The EUP2571 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 EUP2571 switches at 1.1MHz, allowing the use of tiny external components. The input and output capacitor can be as small as 1F, saving space and cost versus alternative solutions. A low 0.25V feedback voltage minimizes power loss in the current setting resistor for better efficiency. The EUP2571 is available in low profile SOT23-5, SOT23-6 package.
FEATURES
2.6V to 5.5V Input Range 26V Output with Over Voltage Protection High Efficiency :85 % Typical PWM Dimming Control Internal High Power 30V MOSFET Switch Fast 1.1MHz Switching Frequency Small, Low-Profile Inductors and Capacitors SOT23-5,SOT23-6 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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Typical Application Circuit (continued)
Figure 2. 5V to 9V/300mA Step-Up Application
Pin Configurations
Package Type Pin Configurations Package Type Pin Configurations
SOT23-5
SOT23-6
Pin Description
PIN LX GND FB EN IN OUT SOT23-5 1 2 3 4 5 SOT23-6 1 2 3 4 6 5 DESCRIPTION Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to reduce EMI. Common Ground Feedback Pin. Reference voltage is 0.25V. Connect cathode of lowest LED and resistor here. Calculate resistor value according to the formula: RFB=0.25/ILED Chip Enable Pin. Connect to 1.4V or higher to enable device, 0.4V or less to disable device. Input Supply Voltage 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 1uF capacitor from OUT to GND.
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Ordering Information
Order Number EUP2571VBIR1 EUP2571VCIR1 Package Type SOT23-5 SOT23-6 Marking Operating Temperature range 1/4 1/4 1/4 -40 C to 125C -40 C to 125C
V0 1/4
1/4
V0 1/4
EUP2571 1/4
1/4
1/4
1/4
Lead Free Code 1: Lead Free 0: Lead Packing R: Tape & Reel Operating temperature range I: Industry Standard Package Type V: SOT23 VB: SOT23-5 VC: SOT23-6
Block Diagram
Figure 3.
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Absolute Maximum Ratings
Supply Voltage ,VIN ----------------------------------------------------------------- -0.3V to 6V LX,OUT ----------------------------------------------------------------------------- -0.3V to 30V The Other Pins ---------------------------------------------------------------------- -0.3V to 6V Power dissipation, PD@ TA=25C SOT23-6 ------------------------------------------------------------------------------- 0.4W Package Thermal Resistance SOT23-6,c JA ------------------------------------------------------------------------- 250C/W Maximum Junction Temperature --------------------------------------------------- 125C Lead Temperature (Soldering, 10sec.) --------------------------------------------- 260C Storage Temperature Range ------------------------------------------------------- -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=12V, COUT=1F, CIN=1F, RSENSE=12[, Typical values are at TA= 25C) TA=-40C to 85C. Unless otherwise noted.
Symbol
UVLO ICC1 ICC2 ICC3 Oscillator Fosc Dmax
Parameter
Supply Voltage Under voltage Lock Out Maximum Output Voltage Supply Current Quiescent Current Shut Down current Operation Frequency Maximum Duty Cycle TA=25J
Conditions
VIN rising or falling VCC=6V, Continuous Switching VCC=6V, FB=1.3V, No Switching VCC=6V, VEN<0.4V
EUP2571 Min Typ Max.
-2.2 ----0.8 89 237 230 -0.4 0.4 ---2.4 -0.8 115 0.1 1.1 92 250 250 1.05 0.75 0.7 0.7 -25.7 27.3 6 2.6 26 1.5 250 1 1.3 96 263 270 1.5 1.2 -1.2 0.1 26.5 28.1
Unit
V V V mA A A MHz %
Reference Voltage VFB Feedback Voltage TA=-40C to 85C mV
MOSFET Rds (on) On resistance of MOSFET ILX Current Limit Control and Protection VEN1 Shut Down Voltage VEN2 IEN OVP Enable Voltage EN Pin Pull Low Current OVP Threshold Falling Rising
[ A V V A V
24.5 26.1
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Typical Operating Characteristics
Efficiency vs. Vin (Driving 1WLED) Efficiency vs. Vin (Driving 2WLEDs)
Efficiency vs. Vin (Driving 3WLEDs)
Efficiency vs. Vin (Driving 5WLEDs)
Efficiency vs. Vin (Driving 7WLEDs)
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Application Information
LED Current Control The EUP2571 regulates the LED current by setting the current sense resistor (R2) connecting to feedback and ground. The internal feedback reference voltage is 0.25V. The LED current can be set from following equation easily.
R2 = 0.25V I LED
--------------------------------------(1)
In order to have an accurate LED current, precision resistors are preferred (1% is recommended). The table for R2 selection is shown below. R2 Resistor Value selection ILED (mA) 5 10 12 15 20 R2 ([ 49.9 24.9 21 16.5 12.4 )
Figure 4. PWM Dimming Control Using the EN Pin 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 5. According to the Superposition Theorem, as the DC voltage increases, the voltage contributed to VFB increases and the voltage drop on R2 decreases, i.e. the LED current decreases. For example, if the VDC range is from 0V to 2.8V, the selection of resistors in Figure 5 sets dimming control of LED current from 20mA to 0mA.
Inductor Selection The recommended value of inductor for 2 to 6 WLEDs applications are 4.7 to 22H. Small size and better efficiency are the major concerns for portable device, such as EUP2571 used for mobile phone. The inductor should have low core loss at 1.1MHz and low DCR for better efficiency. To avoid inductor saturation current rating should be considered. Dimming Control a. Using a PWM Signal to EN Pin For controlling the LED brightness, the EUP2571 can perform the dimming control by applying a PWM signal to EN pin. 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 5. Dimming Control Using a DC Voltage
Figure 6. Recommended Soft-Start Circuit
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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. The recommended application circuit is shown in the Figure 7. In this circuit, the output ripple depends on the frequency of PWM signal. For smaller output voltage ripple (<100mV), the recommended frequency of 2.8V 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 7, output current is from 20.5mA to 5.5mA by adjusting the PWM duty cycle from 10% to 90%. Constant Output Voltage for Backlight of Main Panel and Flashlight Figure 8 is an application of EUP2571 for backlight of main panel and flashlight. Setting the divider-resistors (R1 & R2) is to get a constant output voltage that depends on the forward voltage and the numbers of series-LEDs. There are three kinds of mode controlled by the switches - backlight mode /flashlight mode /backlight + flashlight mode. It can turn on backlight or flashlight at one time or both at the same time. Applying different duty cycle of PWM signal above 22kHz to backlight's switch can also control the brightness. The following formula (2)(3) can determine R3 and R4.
R3 = R4 = VOUT - 3VFb - VDS --------------------------(2) Ib VOUT - 3VFf - VDS --------------------------(3) If
VDS = Ib x R DS(ON ) ---------------------------------(4)
Figure 7. Filtered PWM Signal for LED Dimming Control
Figure 8. Constant Output Voltage for Backlight and Flashlight
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Constant Output Voltage for Backlight of Main Panel and Keypad Figure 9 is another application of EUP2571 for backlight and keypad. Setting the divider-resistors (R1 & R2) is to get a constant output voltage that depends on the forward voltage and the numbers of series-LEDs. It can turn on backlight of main panel and keypad at the same time. Applying different duty cycle of PWM signal above 22kHz to the backlight's switch can also control the brightness of main panel's backlight. The keypad's backlight will keep the same brightness during the dimming control of main panel. Otherwise the brightness of keypad's s backlight can also change during the dimming control of main panel by using the application circuit as figure 5. The following formula (5)(6) can determine the resistors of Figure 9.
R3 = VOUT - 3VFb - VDS ----------------------------(5) Ib
R4 = R5 = R6 =
VOUT - 3VFk ----------------------(6) Ik
VDS = Ib x R DS(ON) ----------------------------------(7)
Figure 9. Constant Output Voltage for Backlight and Keypad
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Packaging Information
SOT23-5
SYMBOLS A A1 D E1 E L b e
MILLIMETERS MIN. 0.00 2.90 1.60 2.60 0.30 0.30 0.95 3.00 0.60 0.50 0.102 0.012 0.012 MAX. 1.30 0.15 MIN. 0.000
INCHES MAX. 0.052 0.006 0.114 0.063 0.118 0.024 0.020 0.037
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Packaging Information
SOT23-6
SYMBOLS A A1 b D E1 e E L
MILLIMETERS MIN. MAX. 1.45 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. 0.057 0.006 0.020
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