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PDF LX1990 Data sheet ( Hoja de datos )
| Número de pieza | LX1990 | |
| Descripción | Dual Programmable LED Current Sink | |
| Fabricantes | Microsemi Corporation | |
| Logotipo |  |
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INTEGRATED PRODUCTS
LX1990
Dual Programmable LED Current Sink
DESCRIPTION
The LX1990 is a dual output current Light output from LED’s is proportional
sink optimized for driving light emitting to average current through them; they can
diodes. This low cost bipolar IC enables easily produce a brightness range of 500:1.
precise current regulation in LED However, color of emitted light is shifted
display lighting applications, yet by current amplitude. Color shift at low
requires far fewer parts than discrete light levels can be reduced by driving the
solutions. The LX1990 is supplied in a LED’s with a constant peak current while
micro-miniature 6 lead MLP package dimming with duty cycle control.
featuring a 3 x 3 mm footprint, a profile This is achieved by driving the ISET
of less than 1mm, and much improved resistor with a PWM signal. A 500:1
thermal performance. Its two output sink brightness range can be achieved by
currents are accurately matched and choosing 270 Hz as the PWM frequency (to
require only one resistor to program. avoid optical beating with 50/60 Hz room
Program current is only 1% of the lights) and pulse width from 3.7
output currents, and quiescent current is milliseconds to 7.4 microseconds.
low, providing a very high efficiency The LX1990 features a shutdown mode
driver for battery-powered displays.
via the Enable pin. In this mode the
The LX1990 is based on a current- LX1990 consumes less than 1µA and holds
mirror architecture that transfers a the two open collector output stages off.
reference current produced at the ISET This pin may also be used to pulse width
pin to each of two open-collector current modulate output current. See applications
sinking outputs. The output stages section for dimming details.
multiply this reference current by 100 to
sink independently regulated currents up
to 30 mA.
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
PRODUCT HIGHLIGHT
KEY FEATURES
• Programmable Sink Current
0.1 to 30mA x 2 Channels
• Replaces Discrete Transistor
Circuitry With A Single Package
• 300mV Maximum Current Sink
Dropout Voltage at 20mA
• 2.7 to 5.5V Power Supply Input
• IOUT Compliance Voltage from
0.1 to 10VDC
• Enable Input With <1µA Sleep
Current
• Amplitude and PWM Dimming
• Current rise and fall time may
be controlled to reduce EMI
APPLICATIONS
• Cell Phone Display Illumination
• PDA White LED Display
Lighting
• Automotive Display Illumination
• Digital Still Camera
• Camcorders
• Consumer Electronics Front
Panels
5V
ON/OFF
RSET
VLOAD
VDD
ENA
IOUTB
LX1990
ISET
IOUTA
GND
Copyright 2001
Rev. 1.0c, 2002-05-29
PACKAGE ORDER INFO
TA (°C)
Plastic MLP
LM 6-Pin
-40 to 85
LX1990ILM
Note: Available in Tape & Reel.
Append the letter “T” to the part number. (i.e. LX1990ILM-T)
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
1 page  
INTEGRATED PRODUCTS
LX1990
Dual Programmable LED Current Sink
APPLICATIONS
FUNCTIONAL DESCRIPTION
The LX1990 is designed to drive LED’s used in display
illumination and signaling applications such as cellular
telephones and PDA’s. With a 5V supply, the two
independently regulated constant current outputs can drive
2 white LED’s (VF < 4.5V) in parallel, or 4 green or
amber LED’s (VF < 2.25V each) arranged as 2 parallel x 2
in series.
With Dropout voltage of only 300 mV at 20 mA, the
LX1990 provides regulated current for 2 green / amber
LED’s in a cell phone all the way down to the minimum
NiCd cutoff of 2.7 volts for three cells.
The LX1990 features resistor settable output current.
Connecting a resistor between ISET and a voltage of zero to
1.25 volts generates a current that is mirrored into each of
the output with a gain of about 100. Output current can be
varied in an analog fashion by varying ISET resistance or
termination voltage (see application schematics).
Duty cycle dimming with a fixed current amplitude is
accomplished by switching the ISET current on and off
with an open collector or open drain pulse width
modulated logic signal. Switching frequency can exceed
20 KHz, making it practical to use a PWM output channel
from popular micro controllers. The upper limit on
frequency is minimum switching response from ISET to
output. As frequency increases, these fixed delays will
cause an error in expected output current duty cycle.
All inputs and outputs are ESD and short circuit
protected making the LX1990 an exceptionally robust
component. However it is not recommended to
indefinitely short the ISET input to ground while shorting
the outputs to 10V as the power dissipation under these
conditions is the greatest.
APPLICATION NOTES
Each output has an independent current sink, however
both must be held above about 0.5 volts to maintain
specified current regulation accuracy. If only one output
is needed, the two outputs should be connected together
and the programming resistor value doubled so each
output supplies ½ the desired current. In this case, more
than 60 mA total current can be delivered from the
combined output.
Package power dissipation can be calculated from the
following equation:
( ) ( )PD = n⋅ IOUT ⋅ VLOAD − VL ED
n
IOUT
VLOAD
VLED
PD
= Number of outputs used
= Current from each output
= Output Supply Voltage
= Minimum LED forward voltage
= Power Dissipated in mW
When the ENA input is at zero volts, less than 20µA
current flows into or out of the outputs. If the disable
function is used , ENA must be driven below 0.4 volts to
insure minimum current from VDD.
The ISET pin may be driven with a digital open collector or
open drain logic PWM signal to dim the LED’s.
Recommended PWM frequency for dimming is between
100 Hz and 20 KHz. Below 100 Hz flicker may be
observed. Above 20 KHz duty cycle accuracy is reduced due
to switching delays from ISET to outputs. Totem pole output
drive may also be used as long as the maximum driver
voltage never exceeds the VDD supply. Since the totem pole
drive will exceed the 1.25V ISET voltage it can introduce
delays that may limit the useful frequency and maximum
dim range.
If PWM dimming is used, use separate power and ground
lines directly from the power source point to prevent noise
generated from the LED current transients from entering
video or audio subsystems on the same supply rails.
Additional power supply filtering may be needed in PWM
dimming applications. Care should be exercised in the PCB
layout to prevent coupling from the outputs to the ISET pin,
as this may cause the part to oscillate.
Current out of the ISET pin may be varied for current
amplitude dimming. There are two ways to do this: If a
mechanical input is needed, a rheostat in series with a
resistor connected from GND to ISET can be used. The
second method is to connect a fixed resistor from ISET to the
output of a voltage DAC or other low impedance voltage
source. Varying the voltage between zero and 1.25 volts will
cause a corresponding output current change from IOUT max
to zero:
IOUT = Current Ratio × ISET
The ENA pin may be used to duty cycle dim the output
in applications where only one control line is available for
dimming and shutdown. A narrow current spike that may be
as high as 100 mA is produced when the ENA signal has
very fast rise times. This is not harmful to the LED, but will
cause dimming linearity errors when operating at very low
duty cycles.
Copyright 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 5
5 Page 
INTEGRATED PRODUCTS
LX1990
Dual Programmable LED Current Sink
NOTES
Copyright 2001
Rev. 1.0c, 2002-05-29
PRODUCTION DATA – Information contained in this document is proprietary to Microsemi
and is current as of publication date. This document may not be modified in any way without
the express written consent of Microsemi. Product processing does not necessarily include
testing of all parameters. Microsemi reserves the right to change the configuration and
performance of the product and to discontinue product at any time.
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 11
11 Page | ||
| Páginas | Total 11 Páginas | |
| PDF Descargar | [ Datasheet LX1990.PDF ] | |
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