LX1990ILM MICROSEMI, LX1990ILM Datasheet - Page 5

• Manufacturer Part Number: LX1990ILM
• Manufacturer: MICROSEMI

Specifications of LX1990ILM

• Operating Supply Voltage (typ): 3.3/5V
• Number Of Segments: 2
• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Package Type: MLP
• Pin Count: 6
• Mounting: Surface Mount
• Operating Supply Voltage (min): 2.7V
• Operating Supply Voltage (max): 5.5V
• Lead Free Status / RoHS Status: Compliant

Copyright © 2001
Rev. 1.0d, 2005-03-14
F
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 (V
amber LED’s (V
in series.
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.
Connecting a resistor between I
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 I
termination voltage (see application schematics).
accomplished by switching the I
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 I
output. As frequency increases, these fixed delays will
cause an error in expected output current duty cycle.
protected making the LX1990 an exceptionally robust
component. However it is not recommended to
indefinitely short the I
the outputs to 10V as the power dissipation under these
conditions is the greatest.
A
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.
UNCTIONAL
The LX1990 is designed to drive LED’s used in display
With Dropout voltage of only 300 mV at 20 mA, the
The LX1990 features resistor settable output current.
Duty cycle dimming with a fixed current amplitude is
All inputs and outputs are ESD and short circuit
Each output has an independent current sink, however
PPLICATION
following equation:
Package power dissipation can be calculated from the
TM
P
D
D
N
ESCRIPTION
OTES
=
F
< 2.25V each) arranged as 2 parallel x 2
(
F
n
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: [phone]
⋅
< 4.5V) in parallel, or 4 green or
I
SET
OUT
input to ground while shorting
) (
⋅
V
SET
LOAD
SET
and a voltage of zero to
−
current on and off
V
SET
L
ED
resistance or
)
A P P L I C A T I O N S
Integrated Products
®
Microsemi
SET
to
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 V
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 I
drive may also be used as long as the maximum driver
voltage never exceeds the V
drive will exceed the 1.25V I
delays that may limit the useful frequency and maximum
dim range.
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 I
as this may cause the part to oscillate.
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 I
second method is to connect a fixed resistor from I
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 I
to zero:
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.
Dual Programmable LED Current Sink
n
I
V
V
When the ENA input is at zero volts, less than 20µA
The I
If PWM dimming is used, use separate power and ground
Current out of the I
P
OUT
LOAD
LED
D
The ENA pin may be used to duty cycle dim the output
SET
pin may be driven with a digital open collector or
=
=
=
=
=
I
OUT
Number of outputs used
Current from each output
Output Supply Voltage
Minimum LED forward voltage
Power Dissipated in mW
=
Current
SET
SET
pin may be varied for current
DD
to outputs. Totem pole output
supply. Since the totem pole
SET
DD
Ratio
.
voltage it can introduce
SET
×
I
can be used. The
SET
LX1990
SET
OUT
SET
to the
max
pin,
Page 5