ETC EUP2518

芯美电子
EUP2518
White LED Step-Up Converter
In TSOT-23 Package
DESCRIPTION
FEATURES
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.
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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EUP2518
Pin Configurations
Package Type
Pin
Configurations
TSOT23-6
Pin Description
PIN
TSOT23-6
LX
1
Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to reduce EMI.
GND
2
FB
3
EN
4
OUT
5
IN
6
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
DS2518 Ver1.0 Mar. 2008
DESCRIPTION
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EUP2518
Ordering Information
Order Number
Package Type
Marking
Operating Temperature Range
EUP2518OIR1
TSOT23-6
50 □ □ □ □
-40 °C to 85°C
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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EUP2518
Absolute Maximum Ratings
Supply Voltage ,VIN ----------------------------------------------------------------LX,OUT ----------------------------------------------------------------------------The Other Pins ---------------------------------------------------------------------Package Thermal Resistance
TSOT23-6,θJA ----------------------------------------------------------------------Maximum Junction Temperature --------------------------------------------------Lead Temperature (Soldering, 10sec.) --------------------------------------------Storage Temperature Range ---------------------------------------------------------
-0.3V to 6V
-0.3V to 30V
-0.3V to 6V
220°C/W
125°C
260°C
-65°C to 150°C
Operating Conditions
Junction Temperature Range ------------------------------------------------------- -40°C to 125°C
Supply Voltage , VIN----------------------------------------------------------------- 2.6V to 5.5V
Electrical Characteristics
(VIN =3.6V, VOUT=18V, COUT=0.22µF, CIN=1µF, RFB=5.1Ω, TA=-40°C to 85°C. Unless otherwise noted. Typical
values are at TA= 25°C)
Symbol
Parameter
Conditions
Supply Voltage
UVLO
ICC1
ICC2
ICC3
Under Voltage Lock Out
Maximum Output Voltage
Supply Current
Quiescent Current
Shutdown current
VIN Rising
VIN Falling
No Switching
VCC=6V, Continuous Switching
VCC=6V, FB=1.3V, No Switching
VCC=6V, VEN<0.3V
Min
EUP2518
Typ
Max.
Unit
-2.2
1.95
-----
-2.4
2.15
-0.8
115
0.1
6
2.6
2.35
30
1.3
150
1
V
V
mA
µA
µA
V
Oscillator
Fosc
Operation Frequency
0.8
1.1
1.3
MHz
Dmax
Maximum Duty Cycle
89
92
96
%
Feedback Voltage
94
104
114
mV
On resistance of MOSFET
--
1
1.5
Ω
Current Limit
0.4
0.8
1.2
A
Reference Voltage
VFB
MOSFET
RDS(ON)
ILX
Control and Protection
VEN1
Shutdown Voltage
0.3
0.7
--
V
VEN2
Enable Voltage
--
0.7
1.4
V
EN Pin Pull Low Current
--
--
0.1
µA
Falling
24.5
25.7
26.5
Rising
26.1
27.3
28.1
IEN
OVP
OVP Threshold
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EUP2518
Typical Operating Characteristics
Efficiency vs LED Current
Startup Waveforms into an Open Load
91
VEN
EFFICENCY (%)
87
VOUT
83
79
VSW
6 LED
3 LED
4 LED
75
5
10
15
20
LED CURRENT (mA)
Steady State Operation(VIN=3.6V, 3 LEDs, 20mA)
Startup Waveforms
VEN
VSW
VOUT
VOUT
IL
IIN
10KHz 50% Duty Cycle PWM Dimming
1KHz 50% Duty Cycle PWM Dimming
VEN
VEN
VOUT
VOUT
IIN
IIN
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Application Information
b. Using a DC Voltage
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)
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 (Ω)
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 10µH to 47µH. Small size and better
efficiency are the major concerns for portable device. A
22µH inductor with low DCR (Inductor resistance) is
recommended to improve efficiency. To avoid inductor
saturation current rating should be considered. A 1µF
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.
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.
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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EUP2518
Packaging Information
TSOT23-6
SYMBOLS
A
A1
b
D
E1
e
E
L
DS2518 Ver1.0 Mar. 2008
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
MAX.
0.039
0.006
0.020
0.114
0.063
0.037
0.102
0.012
0.118
0.024
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