LX1990
I N T E G R A T E D
P R O D U C T S
Dual Programmable LED Current Sink
DESCRIPTION
KEY FEATURES
W W W.
Microsemi
.COM
The LX1990 is a dual output current
sink optimized for driving light emitting
diodes. This low cost bipolar IC enables
precise current regulation in LED
display lighting applications, yet
requires far fewer parts than discrete
solutions. The LX1990 is supplied in a
micro-miniature 6 lead MLP package
featuring a 3 x 3 mm footprint, a profile
of less than 1mm, and much improved
thermal performance. Its two output sink
currents are accurately matched and
require only one resistor to program.
Program current is only 1% of the
output currents, and quiescent current is
low, providing a very high efficiency
driver for battery-powered displays.
The LX1990 is based on a current-
mirror architecture that transfers a
reference current produced at the I
SET
pin to each of two open-collector current
sinking outputs. The output stages
multiply this reference current by 100 to
sink independently regulated currents up
to 30 mA.
Light output from LED鈥檚 is proportional
to average current through them; they can
easily produce a brightness range of 500:1.
However, color of emitted light is shifted
by current amplitude. Color shift at low
light levels can be reduced by driving the
LED鈥檚 with a constant peak current while
dimming with duty cycle control.
This is achieved by driving the I
SET
resistor with a PWM signal. A 500:1
brightness range can be achieved by
choosing 270 Hz as the PWM frequency (to
avoid optical beating with 50/60 Hz room
lights) and pulse width from 3.7
milliseconds to 7.4 microseconds.
The LX1990 features a shutdown mode
via the Enable pin. In this mode the
LX1990 consumes less than 1碌A and holds
the two open collector output stages off.
This pin may also be used to pulse width
modulate output current. See applications
section for dimming details.
鈥?/div>
Programmable Sink Current
0.1 to 30mA x 2 Channels
鈥?/div>
Replaces Discrete Transistor
Circuitry With A Single Package
鈥?/div>
300mV Maximum Current Sink
Dropout Voltage at 20mA
鈥?/div>
2.7 to 5.5V Power Supply Input
鈥?/div>
I
OUT
Compliance Voltage from
0.1 to 10V
DC
鈥?/div>
Enable Input With <1碌A Sleep
Current
鈥?/div>
Amplitude and PWM Dimming
鈥?/div>
Current rise and fall time may
be controlled to reduce EMI
APPLICATIONS
鈥?/div>
Cell Phone Display Illumination
鈥?/div>
PDA White LED Display
Lighting
鈥?/div>
Automotive Display Illumination
鈥?/div>
Digital Still Camera
鈥?/div>
Camcorders
鈥?/div>
Consumer Electronics Front
Panels
IMPORTANT:
For the most current data, consult
MICROSEMI鈥檚
website:
http://www.microsemi.com
PRODUCT HIGHLIGHT
5V
VDD
ON/OFF
ENA
I
O UT B
I
O UT A
GND
R
SE T
LX1990
ISET
V
LO AD
LX1990
LX1990
PACKAGE ORDER INFO
Plastic MLP
T
A
(擄C)
擄
LM
6-Pin
-40 to 85
LX1990ILM
Note: Available in Tape & Reel.
Append the letter 鈥淭鈥?to the part number. (i.e. LX1990ILM-T)
Copyright
錚?/div>
2001
Rev. 1.0c, 2002-05-29
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
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