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EUP2571

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 1μF, 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.

Typical Application Circuit

FEATURES

z 2.6V to 5.5V Input Range

z 26V Output with Over Voltage Protection z High Efficiency :85 % Typical z PWM Dimming Control

z Internal High Power 30V MOSFET Switch z Fast 1.1MHz Switching Frequency

z Small, Low-Profile Inductors and Capacitors z SOT23-5,SOT23-6 Package

RoHS Compliant and 100% Lead (Pb)-Free

APPLICATIONS

z Mobile Phone

z Digital Still Camera

z PDAs, Handheld Computers z MP3 Players z GPS Receivers

Figure 1. White LED Application

EUP2571

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 SOT23-5

SOT23-6

DESCRIPTION

LX 1 1

Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to reduce EMI.

GND 2 2 Common Ground

FB 3 3 Feedback Pin. Reference voltage is 0.25V . Connect cathode of lowest LED

and resistor here. Calculate resistor value according to the formula:

R FB =0.25/I LED

EN 4 4

Chip Enable Pin. Connect to 1.4V or higher to enable device, 0.4V or less to

disable device.

IN 5 6 Input Supply V oltage

OUT - 5 Overvoltage Sense. When V OUT is greater than 27V , the internal N-channel

MOSFET turns off until V OUT drops below 25V , then the IC reenters start.

EUP2571

Ordering Information

Order Number Package Type

Marking

Operating Temperature Range

EUP2571VBIR1 SOT23-5 V0 -40 °C to 85°C EUP2571VCIR1 SOT23-6

-40 °C to 85°C

EUP2571

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.

Absolute Maximum Ratings

Supply V oltage ,V IN ----------------------------------------------------------------- -0.3V to 6V

LX,OUT ----------------------------------------------------------------------------- -0.3V to 30V

The Other Pins ---------------------------------------------------------------------- -0.3V to 6V

Power dissipation, P D@ T A=25°C

SOT23-6 ------------------------------------------------------------------------------- 0.4W

Package Thermal Resistance

SOT23-6,￡c JA------------------------------------------------------------------------- 250°C/W

Maximum Junction Temperature --------------------------------------------------- 125°C

Lead Temperature (Soldering, 10sec.) --------------------------------------------- 260°C

Storage Temperature Range ------------------------------------------------------- -65°C to 150°C

Operating Conditions

Junction Temperature Range --------------------------------------------------- -40°C to 125°C

Supply V oltage , V IN----------------------------------------------------------------- 2.6V to 5.5V

Electrical Characteristics

(V IN =3.6V, V OUT=12V, C OUT=1μF, C IN=1μF, RSENSE=12￡,T A=-40°C to 85°C. Unless otherwise noted.

Typical values are at T A= 25°C)

EUP2571

Unit

Symbol Parameter Conditions

Min Typ Max.

V oltage -- -- 6 V Supply

UVLO Under voltage Lock Out V IN rising or falling 2.2 2.4 2.6 V

V oltage -- -- 26 V Maximum

Output

Current V CC=6V, Continuous Switching -- 0.8 1.5 mA

I CC1 Supply

Current V CC=6V, FB=1.3V, No Switching -- 115 250 μA

I CC2 Quiescent

μA

I CC3Shut Down current V CC=6V, V EN<0.4V --

0.1 Oscillator

Frequency 0.8 1.1 1.3 MHz Fosc

Operation

Dmax Maximum Duty Cycle 89 92 96 %

Reference Voltage

T A=25￠J237 250 263

V oltage

V FB Feedback

85°C 230 250 270

T A=-40°C

MOSFET

Rds (on) On resistance of MOSFET -- 1.05 1.5

Limit 0.4 0.75 1.2 A ILX Current

Control and Protection

V oltage 0.4 0.7 -- V Down

V EN1 Shut

V oltage -- 0.7 1.2 V V EN2 Enable

I EN EN Pin Pull Low Current -- -- 0.1 μA

Falling 24.5 25.7 26.5

V OVP OVP

Threshold

Rising 26.1 27.3 28.1

Typical Operating Characteristics

Efficiency vs. Vin (Driving 1WLED)

Efficiency vs. Vin (Driving 3WLEDs)

Efficiency vs. Vin (Driving 7WLEDs)

Efficiency vs. Vin (Driving 2WLEDs)

Efficiency vs. Vin (Driving 5WLEDs)

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.

LED

I 0.25V

R2=--------------------------------------(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

I LED (mA)

R2 (￡)

5 49.9 10 24.9 12 21 15 16.5 20 12.4

Inductor Selection

The recommended value of inductor for 2 to 6 WLEDs applications are 4.7 to 22μH. 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 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 V FB increases and the voltage drop on R2 decreases, i.e. the LED current decreases. For example, if the V DC range is from 0V to 2.8V , the selection of resistors in Figure 5 sets dimming control of LED current from 20mA to 0mA.

Figure 5. Dimming Control Using a DC Voltage

Figure 6. Recommended Soft-Start Circuit

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%.

Figure 7. Filtered PWM Signal for LED

Dimming Control 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.

3VFb

OUT

=--------------------------(2)

3VFf

OUT

=--------------------------(3)

)

(

DS R

V×

=---------------------------------(4)

Figure 8.Constant Output Voltage for Backlight

and Flashlight

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.

V 3VFb OUT V R3??=

----------------------------(5)

3VFk

V R6R5R4OUT ?=

==----------------------(6)

)ON (DS DS R Ib V ×=----------------------------------(7)

Figure 9.Constant Output Voltage for Backlight

and Keypad

SOT23-5

MILLIMETERS INCHES SYMBOL

S MIN. MAX. MIN. MAX.

A - 1.30 - 0.052

A1 0.00 0.15 0.000 0.006

D 2.90 0.114

E1 1.60 0.063

E 2.60 3.00 0.102 0.118

L 0.30 0.60 0.012 0.024

b 0.30 0.50 0.012 0.020

e 0.95 0.037

SOT23-6

MILLIMETERS INCHES SYMBOLS

MIN. MAX. MIN. MAX.

A - 1.45 - 0.057

A1 0.00 0.15 0.000 0.006

b 0.30 0.50 0.012

0.020

D 2.90 0.114

E1 1.60 0.063

e 0.95 0.037

E 2.60 3.00 0.102

0.118

0.024

L 0.3 0.60 0.012