Eutech EUP2561 26v step-up converters for two to six white led Datasheet

26V Step-Up Converters
EUP2561
for Two to Six White LEDs
DESCRIPTION
FEATURES
The EUP2561 is a constant current step-up converter
specially designed for driving white LEDs. The step-up
converter topology allows series connection of the
white LEDs so the LED currents are identical for
uniform brightness. The EUP2561 can drive 6 LEDs in
series. The brightness of the LEDs can be adjusted
through a voltage level on the CTRL pin or by
applying a PWM signal to CRTL pin.
1MHz current-mode, pulse-width modulated (PWM)
operation allows for small input and output capacitors
and a small inductor while minimizing ripple on the
input
supply/battery.
Programmable
soft-start
eliminates inrush current during startup.
The EUP2561 is available in a space-saving, 8-pin
3mm x 3mm DFN package.
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2.6V to 5.5V Input Range
26V (max) Output with Overvoltage Protection
Up to 87% Efficiency
Flexible Analog or PWM Dimming Control
Internal High Power 30V MOSFET Switch
< 1µA shutdown Current
Fast 1MHz PWM Operation
Small, Low-Profile Inductors and Capacitors
3mm × 3mm DFN-8 Package
RoHS Compliant and 100% Lead (Pb)-Free
APPLICATIONS
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Cell Phones and Smart Phones
PDAs, Palmtops, and Wireless Handhelds
e-Books and Subnotebooks
White LED Display Backlighting
Typical Application Circuit
Figure 1. White LED Application
DS2561 Ver1.0
Dec. 2006
1
EUP2561
Pin Configurations
Package Type
Pin Configurations
(Top View)
DFN-8
Pin Description
PIN
Pin
DESCRIPTION
OUT
1
Regulated Output Voltage.
IN
2
CTRL
3
CS
4
COMP
5
GND
6
Input Supply Voltage.
Brightness Control Input. LED brightness is controlled by the voltage applied to
CTRL. Varying the voltage from 0.24V to 1.62V adjusts the brightness from dim to
bright, respectively. Any voltage above 1.62V does not increase brightness.
Current-Sense Feedback Input. Connect a resistor from CS to GND to set the LED bias
current. The voltage at CS regulates to VCTRL / 10 or 0.162V, whichever is lower.
Compensation Input. Connect a 0.1µF capacitor (CCOMP) from COMP to GND.
CCOMP stabilizes the converter and controls soft-start. CCOMP discharges to GND
when in shutdown.
Common Ground. Connect to PGND and the exposed pad directly under the IC.
PGND
7
Power Ground. Connect to GND and the exposed pad directly under the IC.
LX
8
Inductor Connection. This pin is high impedance during shutdown.
DS2561 Ver1.0
Dec. 2006
2
EUP2561
Ordering Information
Order Number
Package Type
Marking
Operating Temperature range
EUP2561JIR1
DFN-8
xxxx
2561A
-40 °C to 125°C
EUP2561
□ □ □
□
Lead Free Code
1: Lead Free 0: Lead
Packing
R: Tape & Reel
Operating temperature range
I: Industry Standard
Package Type
J: DFN-8
Block Diagram
Figure 2.
DS2561 Ver1.0
Dec. 2006
3
EUP2561
Absolute Maximum Ratings
IN to GND -------------------------------------------------------------------------- -0.3V to 6V
PGND to GND ---------------------------------------------------------------------- -0.3V to 0.3V
LX,OUT to GND ------------------------------------------------------------------- -0.3V to 30V
CTRL to GND -------------------------------------- -0.3V to the lower of 6V or (VIN +0.5V)
COMP,CS to GND ---------------------------------------------------------- -0.3V to (VIN +0.3V)
ILX ------------------------------------------------------------------------------------- 1A
Thermal Resistance
DFN-8 -------------------------------------------------------------------------------- 50°C /W
Junction Temperature ---------------------------------------------------------------- 150°C
Storage Temperature Range ------------------------------------------------------ -65°C to 150°C
Lead Temperature (Soldering, 10sec.) --------------------------------------------- 260°C
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Recommended Operating Conditions
Supply Voltage, VIN ---------------------------------------------------------------- 2.6V to 5.5V
Operating Temperature Rang ----------------------------------------------------- -40°C to 85°C
„
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Electrical Characteristics
(VIN = 3V, VOUT = 20V, COUT = 0.1µF, CCOMP = 0.15µF, RSENSE = 7.5Ω, VCTRL = 1.5V, Figure 2,
TA =-40°C to +85°C, unless otherwise noted.)
Parameter
EUP2561
Min
Typ
Max.
Conditions
2.6
Supply Voltage
5.5
V
2.40
2.60
V
0.39
0.60
mA
V
UVLO Threshold
VIN rising or falling
Quiescent Current
No Switching
OVLO Threshold
VOUT rising
26
27.5
29
VOUT=26V,VCTRL> 0.24V
12
22
35
0.01
1
OUT Input Bias Current
2.20
VOUT=VIN, CTRL=GND
(VIN-VD1)
Output Voltage Range
ERROR AMPLIFIER
CTRL to CS Regulation
CTRL Input Resistance
VCTRL = 1V, VIN= 2.6V to 5.5V
VCTRL ≤ 1.0V
CTRL Dual-Mode
Threshold
CTRL Shutdown Enable
Delay
CS-to-COMP
Transconductance
OSCILLATOR
Operating Frequency
Rising
Maximum Duty Cycle
CTRL=IN CS=GND
µA
25.5
V
0.095
0.100
0.105
200
400
700
V
kΩ
100
180
260
mV
7.5
Vcomp=1.0V
Unit
mS
21
52
85
µS
0.78
1.05
1.3
MHz
88
92
96
%
1.6
2.4
Ω
750
1000
mA
N-CHANNEL SWITCH
LX On-Resistance
LX Current Limit
DS2561 Ver1.0
Dec. 2006
Duty cycle=90%
550
4
EUP2561
Typical Operating Characteristics
DS2561 Ver1.0
Dec. 2006
5
EUP2561
DS2561 Ver1.0
Dec. 2006
6
EUP2561
Application Information
Soft-Start
The EUP2561 attain soft-start by charging CCOMP
gradually with a current source. When VCOMP rises above
1.25V, the internal MOSFET begins switching at a
reduced duty cycle. When VCOMP rises above 2.25V, the
duty cycle is at its maximum. See the Typical Operating
Characteristics for an example of soft-start operation.
Shutdown
The EUP2561 enter shutdown when VCTRL is less than
100mV for
more
than
8.2ms. In shutdown,
supply current is reduced to 0.3µA by powering down
the entire IC except for the CTRL voltage-detection
circuitry. CCOMP is discharged during shutdown, allowing
the device to reinitiate soft-start when it is enabled.
Although the internal N-channel MOSFET does not
switch in shutdown, there is still a DC current path
between the input and the LEDs through the inductor
and Schottky diode. The minimum forward voltage of
the LED array must exceed the maximum input voltage
to ensure that the LEDs remain off in shutdown.
However, with two or more LEDs, the forward voltage is
large enough to keep leakage current low, less than
1µA(typ). Typical shutdown timing characteristics are
shown in the Typical Operating Characteristics.
Overvoltage Protection
Overvoltage lockout (OVLO) occurs when VOUT is
above 27V.The protection circuitry stops the internal
MOSFET from switching and causes VCOMP to decay to
0V. The device comes out of OVLO and into softstart
when VOUT falls below 25V.
Adjusting LED Current
Adjusting the EUP2561 output current changes
the brightness of the LEDs. An analog input
(CTRL) and the sense-resistor value set the output
current. Output current is given by:
The VCTRL voltage range for adjusting output current is
0.24V to 1.62V. To set the maximum current, calculate
RSENSE when VCTRL is at its maximum as follows:
1.62V
10 × I LED(MAX)
Power dissipation in RSENSE is typically less than 5mW,
making a standard chip resistor sufficient.
DS2561 Ver1.0
Dec. 2006
CTRL is also used as a digital input allowing LED
brightness control with a logic-level PWM signal
applied directly to CTRL. The frequency range is
from 200Hz to 200kHz, while 0% duty cycle
corresponds to zero current and 100% duty cycle
corresponds to full current. The error amplifier and
compensation capacitor form a lowpass filter so PWM
dimming results in DC current to the LEDs without the
need for any additional RC filters; see the Typical
Operating Characteristics.
Capacitor Selection
The exact values of input and output capacitors are not
critical. The typical value for the input capacitor is
2.2µF and the typical value for the output capacitor is
0.1µF. Larger value capacitors can be used to reduce
input and output ripple, but at the expense of size and
higher cost. CCOMP stabilizes the converter and controlls soft-start. Connect a 0.1µF capacitor from
COMP to GND. For stable operation, COUT must not
exceed 10 times CCOMP.
Inductor Selection
Inductor values range from 10µH to 47µH.
A 22µH inductor optimizes the efficiency for most
applications while maintaining low 15mVP-P input
ripple. With input voltages near 5V, a larger value of
inductance can be more efficient. To prevent core
saturation, ensure that the inductor-saturation current
rating exceeds the peak inductor current for the application. Calculate the peak inductor current with the following formula:
I PEAK =
+
VOUT(MAX) × I LED(MAX)
0.8 × VIN(MIN)
VIN(MIN) × 0.8µs
2× L
Schottky Diode Selection
VCTRL
I LED =
10 × R SENSE
R SENSE =
PWM Dimming Control
7
The EUP2561 high switching frequency demands a
high-speed rectification diode (D1) for optimum
efficiency. A Schottky diode is recommended due to its
fast recovery time and low forward-voltage drop.
Ensure that the diode’s average and peak current rating
exceed the average output current and peak inductor
current. In addition, the diode’s reverse breakdown
voltage must exceed VOUT. The RMS diode current can
be calculated from:
I DIODE(RMS) ≅ I OUT × I PEAK
EUP2561
PC Board Layout
Due to fast switching waveforms and high-current
paths, careful PC board layout is required. An evaluation kit is available to speed design.
When laying out a board, minimize trace lengths
between the IC and RSENSE, the inductor, the diode, the
input capacitor, and the output capacitor. Keep traces
short, direct, and wide. Keep noisy traces, such as the
LX node trace, away from CS. The IN bypass
capacitor (CIN) should be placed as close to the IC as
possible. PGND and GND should be connected
directly to the exposed paddle underneath the IC. The
ground connections of CIN and COUT should be as close
together as possible. The traces from IN to the inductor
and from the Schottky diode to the LEDs may be
longer.
DS2561 Ver1.0
Dec. 2006
8
EUP2561
Packaging Information
DFN-8
SYMBOLS
A
A1
b
D
D1
E
E1
e
L
DS2561 Ver1.0
Dec. 2006
MILLIMETERS
MIN.
MAX.
0.70
0.90
0.00
0.05
0.20
0.40
2.85
3.15
2.30
2.85
3.15
1.50
0.65
0.25
0.45
9
INCHES
MIN.
0.028
0.000
0.008
0.112
MAX.
0.035
0.002
0.016
0.124
0.090
0.112
0.124
0.059
0.026
0.010
0.018
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