LX1744
I N T E G R A T E D
P R O D U C T S
Dual Output Boost 鈥?LED Driver / LCD Bias
P
RODUCTION
D
ATASHEET
DESCRIPTION
The LX1744 is a compact high
efficiency step-up boost regulator for
driving white or color LEDs in LCD
lighting applications while supplying the
necessary LCD bias voltage with an
additional integrated boost converter.
Designed for maximum efficiency and
featuring a psuedo-hysteretic PFM
topology (that decreases output voltage
ripple), the LX1744 minimizes system cost
and condenses layout area making it ideal
for PDA, smart-phone, and digital camera
applications.
While the LCD Bias generation is
implemented using an internal N-Channel
MOSFET, the LED driver utilizes an
external N-Channel MOSFET in order to
maintain maximum efficiency along with
flexible power requirements.
The LX1744鈥檚 control circuitry is
optimized for portable systems with a
shutdown current of less than 1碌A(chǔ). The
input voltage range of 1.6V to 6.0V allows
for a wide selection of system battery
voltages and start-up is guaranteed at a V
IN
equal to 1.6V with sustained operation as
low as 1.1V.
The maximum LED drive current is
easily programmed using one external
current sense resistor in series with the
LEDs. In this configuration, LED current
provides a feedback signal to the FB pin,
maintaining constant current regardless of
varying LED forward voltage (V
F
).
Depending on the MOSFET selected, the
LX1744 is capable of achieving an LED
drive in excess of 1.0W.
The LX1744 provides simple dynamic
adjustment of the LED drive current (0% to
100% full range dimming) and the LCD
Bias output voltage (up to
鹵15%
typ)
through separate IC interfaces.
Each
interface has an internal RC filter allowing
designers to make these adjustments via a
direct PWM input signal or an analog
reference signal.
Further, any PWM
amplitude is easily accommodated using a
single external resistor.
The LX1744 is available in the 14-Pin
TSSOP, and the miniature 16-Pin MLP
requiring minimal PCB area.
KEY FEATURES
> 90% Maximum Efficiency
Low Quiescent Supply Current
Externally Programmable Peak
Inductor Current Limit for
Maximum Efficiency
Logic Controlled Shutdown
< 1碌A(chǔ) Shutdown Current
Dynamic Output LED Current
and LCD Bias Voltage
Adjustment via Analog
Reference or Direct PWM Input
14-Pin TSSOP or 16-Pin MLPQ
Package
APPLICATIONS
WWW .
Microsemi
.C
OM
Pagers
Smart Phones
PDAs
Handheld Computers
General LCD Bias Applications
LED Driver
IMPORTANT:
For the most current data, consult
MICROSEMI鈥檚
website:
http://www.microsemi.com
PRODUCT HIGHLIGHT
L
1
I
LED
= 20mA to 0mA
C
1
4.7碌F
V
BAT
= 1.6V to 6.0V
- V
LCD
47碌H
1206 Case Size
DRV
IN
SRC
V
LCD1
= V
IN
to 25V
SW1
OVP
LFB
FB1
CS
LX1744
LSHDN
SW2
REF
FB2
GND
SHDN1
ADJ1
ADJ2
BRT
ON OFF
R
SET
15鈩?/div>
ON OFF
V
LCD2
= V
IN
to 25V
SHDN2
ON OFF
LX1744 Evaluation Board
LX1744
LX1744
PACKAGE ORDER INFO
T
A
(擄C)
-40 to 85
PW
Plastic TSSOP
14-Pin
LQ
Plastic MLP-Q
16-Pin
LX1744CLQ
RoHS Compliant / Pb-free
Transition DC: 0442
RoHS Compliant / Pb-free
Transition DC: 0430
LX1744CPW
Note: Available in Tape & Reel.
Append the letters 鈥淭R鈥?to the part number. (i.e. LX1744CLQ-TR)
Copyright
漏
2000
Rev. 1.1b, 2005-03-01
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
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