ETC EUP2538

芯美电子
EUP2538
10 White LED Boost Converter
In Thin SOT-23 Package
FEATURES
DESCRIPTION
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The EUP2538 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 EUP2538 switches at 1MHz,
allowing the use of tiny external components. The
output capacitor can be as small as 0.22µF, saving
space and cost versus alternative solutions. A low
0.3V feedback voltage minimizes power loss in the
current setting resistor for better efficiency. The
EUP2538 high-voltage output stage is perfect for
driving mid-size and large panel displays containing
up to ten white LEDs in series. LED dimming can be
done by using a DC voltage, a logic signal, or a pulse
width modulation(PWM) signal. The enable input pin
allows the device to be placed in shutdown mode with
“zero” quiescent current.
2.6V to 5.5V Input Range
38V Output with Over Voltage Protection
Internal Soft-Start
PWM Dimming Control
Internal High Power 40V MOSFET Switch
Fast 1MHz Switching Frequency
Small, Low-Profile Inductors and Capacitors
TSOT23-5 Package
RoHS Compliant and 100% Lead (Pb)-Free
APPLICATIONS
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The EUP2538 is available in low profile TSOT23-5
package.
GPS Navigation Systems
Portable Media Players
Handheld Devices, Digital Camera
Portable Game Machines
Typical Application Circuit
Figure 1. White LED Application
DS2538
Ver1.0
May 2008
1
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EUP2538
Pin Configurations
Package Type
Pin
Configurations
TSOT23-5
Pin Description
PIN
TSOT23-5
SW
1
GND
2
FB
3
EN
4
IN
5
DS2538
Ver1.0
May 2008
DESCRIPTION
Switch Pin.This is the drain of the internal power switch. Connect inductor/diode here.
Minimize trace area at this pin to reduce EMI.
Common Ground. Connect the pin to the ground plane.
Feedback Pin. Reference voltage is 0.3V. Connect cathode of lowest LED and resistor
here. Calculate resistor value according to the formula: RFB=0.3/ILED
Chip Enable Pin. Connect to 1.4V or higher to enable device, 0.3V or less to disable
device.
Input Supply Voltage
2
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EUP2538
Ordering Information
Order Number
Package Type
Marking
Operating Temperature Range
EUP2538OIR1
TSOT23-5
20XXXX
-40 °C to 85°C
EUP2538 □ □ □ □
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.
DS2538
Ver1.0
May 2008
3
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芯美电子
EUP2538
Absolute Maximum Ratings
„
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Supply Voltage ,VIN ----------------------------------------------------------------SW ----------------------------------------------------------------------------------The Other Pins ---------------------------------------------------------------------Power dissipation, [email protected] TA=25°C
TSOT23-5 ----------------------------------------------------------------------------Package Thermal Resistance
TSOT23-5,θJA ----------------------------------------------------------------------Maximum Junction Temperature --------------------------------------------------Lead Temperature (Soldering, 10sec.) --------------------------------------------Storage Temperature Range ---------------------------------------------------------
-0.3V to 6V
-0.3V to 40V
-0.3V to 6V
0.4W
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=34V, COUT=0.22µF, CIN=2.2µF, L1=22µH, RFB=15Ω,TA=-40°C to 85°C. Unless otherwise noted.
Typical values are at TA= 25°C)
Symbol
Parameter
Conditions
Supply Voltage
Under Voltage Lock Out
Maximum Output Voltage
Supply Current
Quiescent Current
Shutdown current
UVLO
ICC1
ICC2
ICC3
Rising
No Switching
VCC=6V, Continuous Switching
VCC=6V, FB=1.3V, No Switching
VCC=6V, VEN<0.4V
EUP2538
Min
Typ
Max.
2.2
Unit
1.7
130
0.1
6
2.6
40
2.6
170
1
V
V
V
mA
µA
µA
1
1.3
MHz
2.4
Oscillator
Fosc
Operation Frequency
Dmax
Maximum Duty Cycle
0.8
92
%
Reference Voltage
VFB
Feedback Voltage
285
300
315
mV
0.65
1.3
Ω
0.4
0.75
1.6
A
0.4
0.7
MOSFET
Rds (on) On resistance of MOSFET
ILX
Current Limit
Control and Protection
VEN1
Shutdown Voltage
VEN2
Enable Voltage
0.7
1.2
V
EN Pin Pull Low Current
0.1
1
µA
OVP Threshold
38
IEN
OVP
DS2538
Ver1.0
May 2008
4
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V
芯美电子
EUP2538
Typical Operating Characteristic
Quiescent Current vs. VIN
(Not Switching)
Quiescent Current vs. VIN
(Switching)
2
Quiescent Current (mA)
Quiescent Current (µA)
150
125
VFB=1.3V
100
75
1.5
1
0.5
0
50
3
3.5
4
4.5
5
Input Voltage (V)
3
5.5
4
4.5
5
5.5
Input Voltage (V)
FB PIN Voltage vs. Temperature
310
3.5
310
FB PIN Voltage vs. Output Current
FB PIN Voltage (mV)
FB PIN Voltage (mV)
308
306
304
302
305
300
295
300
10LEDs
298
-50
290
0
50
100
150
5
Temperature (℃)
15
20
25
30
Output Current (mA)
Switching Frequency vs. Supply Voltage
LED Current vs. Input Voltage
40
1.1
35
LED Current (mA)
Switching Frequency (MHz)
10
1
0.9
RFB=10Ω
30
25
RFB=15Ω
20
15
RFB=20Ω
10
5
0
0.8
3
3.5
4
4.5
5
5.5
3
Input Voltage (V)
DS2538
Ver1.0
May 2008
3.5
4
4.5
Input Voltage (V)
5
5
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5.5
芯美电子
EUP2538
1
100
0.5
90
LED Current (mA)
LED Current Variation (%)
Typical Operating Characteristics (continued)
LED Current Regulation (10mA)
0
-0.5
Efficiency vs. Load Current (10 LEDs)
80
70
vin=3.6v
vin=5v
-1
60
3
3.5
4
4.5
5
5.5
5
10
15
Input Voltage (V)
100
20
25
30
Efficiency (%)
Efficiency vs. Input Voltage (10LEDs)
2
Switch On Resistance vs. Input Voltage
Switch Resistance (Ω)
95
Efficiency (%)
90
85
80
75
70
15mA
65
1.5
1
0.5
20mA
60
0
3
3.5
4
4.5
Input Voltage (V)
5
5.5
3
Maximum Output Current vs. Input Voltage
120
3.5
4
4.5
Input Voltage (V)
5
5.5
Shutdown Voltage vs. Input Voltage
1
Shutdown Voltage (V)
Output Current (mA)
100
80
60
40
20
0.6
-40℃
0.4
-25℃
85℃
0
125℃
0.2
3
DS2538
0.8
Ver1.0
3.5
4
4.5
Input Voltage (V)
May 2008
5
5.5
3
3.5
4
4.5
Input Voltage (V)
6
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芯美电子
EUP2538
Typical Operating Characteristics (continued)
Light Load Switching Waveform
VIN=5V, ILED=1.5mA, L=22µH
Typical Switching Waveforms
SW
SW
20V/div
20V/div
Inductor
Inductor
Current
Current
100mA/d
100mA/d
VOUT
VOUT
AC Coupled
AC Coupled
20mV/div
100mV/div
Power-up With 10 LEDs at 20mA
VEN
5V/div
VOUT
20V/div
Input
Current
100mA/div
DS2538
Ver1.0
May 2008
7
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EUP2538
Application Information
Switching Waveform with 1kHz PWM on EN
VEN
LED Current Control
The EUP2538 regulates the LED current by setting the
current sense resistor (RFB) connecting to feedback and
ground. The internal feedback reference voltage is 0.3V.
The LED current can be set from following equation
easily.
I LED =
0.3
R FB
5V/div
VOUT
20V/div
LED
--------------------------------------(1)
Current
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
LED Current (mA)
RFB (Ω)
5
60
10
30
15
20
20
15
25
12
30
10
20mA/div
Figure 4.
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.
Dimming Control
a. Using a PWM Signal to EN Pin
For controlling the LED brightness, the EUP2538 can
perform the dimming control by applying a PWM
signal to EN pin, and the PWM signal frequency range
is from 100Hz to 100KHz. 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. DC Voltage Dimming Control
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 6. 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 6, output current is from
20.5mA to 5.5mA by adjusting the PWM duty cycle
from 10% to 90%.
Figure 3. Direct PWM Dimming Control
DS2538
Ver1.0
May 2008
8
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芯美电子
EUP2538
Shutdown Voltage (V)
1
Shutdown Voltage vs. Input Voltage
0.8
0.6
-40℃
0.4
-25℃
85℃
125℃
0.2
3
3.5
4
4.5
5
Input Voltage (V)
Figure 6. Filtered PWM Dimming Control
Figure 9.
25
Filtered PWM Dimming (0V to 2.5V)
Enable to Open LED Waveforms
VEN
LED Current (mA)
20
5V/div
15
VOUT
20V/div
10
5
SW
20V/div
0
0
10
20
30
40
50
60
70
80
90
100
PWM Duty Cycle (%)
Figure 10.
Figure 7.
Open Load Shutdown
In the event of an “Open LED” fault condition, the
EUP2538 will continue to boost the output voltage with
maximum power until the output voltage reaches
approximately 38V. Once the output exceeds this level,
the device will cease operation until the EN pin is cycled
off and on.
Thermal Shutdown
Thermal overload protection circuitry has been included
to prevent the device from operating at unsafe junction
temperatures above 150ºC. In the event of a thermal
overload condition the device will automatically
shutdown and wait till the junction temperatures cools to
130ºC before normal operation is resumed.
Capacitors Selection
A 4.7µF to 10µF ceramic input capacitor (CIN) and a
0.22µF to 4.7µF ceramic output capacitor (COUT) are
sufficient for most applications. During Direct PWM
Dimming control, a larger output capacitor will
significantly reduce audio noise induced by output
capacitor, and a smaller will enlarge the audio noise, a
2.2uF COUT is recommended. Under normal condition, a
4.7µF input capacitor is sufficient. For applications with
higher output power, a larger input capacitor of 10µF
may be appropriate. X5R and X7R capacitor types are
ideal due to their stability across temperature range.
Figure 8. Open LED Protection
DS2538
Ver1.0
May 2008
9
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EUP2538
Inductor Selection
The recommended value of inductor for 2 to 10 WLEDs
applications are 4.7µH to 47µH. Small size and better
efficiency are the major concerns for portable device,
such as EUP2538 used for mobile phone. The inductor
should have low core loss at 1MHz and low DCR for
better efficiency. To avoid inductor saturation current
rating should be considered.
Schottky Diode Selection
The current rating of the Schottky diode must exceed the
peak current flowing through it. The Schottky diode
performance is rated in terms of its forward voltage at a
given current. In order to achieve the best efficiency, this
forward voltage should be as low as possible. The
response time is also critical since the driver is operating
at 1MHz.
Board Layout
Careful PC board layout is required due to fast switching.
All components must be placed as close to the device as
possible. Keep the path between the inductor L1, diode D1,
and output capacitor COUT extremely short for minimal
noise and ringing. The feedback components such as the
sense resistor RFB must be kept close to the FB pin to
prevent noise injection on the FB pin trace. The ground
return of CIN and COUT should be tied close to the GND pin.
See the EUP2538 demo board layout for reference.
DS2538
Ver1.0
May 2008
10
联系电话:15999644579 83151715
芯美电子
EUP2538
Packaging Information
TSOT23-5
SYMBOLS
A
A1
D
E1
E
L
b
e
DS2538
Ver1.0
May 2008
MILLIMETERS
MIN.
MAX.
1.00
0.00
0.15
2.90
1.60
2.60
3.00
0.30
0.60
0.30
0.50
0.95
INCHES
MIN.
0.000
MAX.
0.039
0.006
0.114
0.063
0.102
0.012
0.012
0.118
0.024
0.020
0.037
11
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