LX1990-03 EVAL KIT MICROSEMI, LX1990-03 EVAL KIT Datasheet - Page 3

• Manufacturer Part Number: LX1990-03 EVAL KIT
• Manufacturer: MICROSEMI

Specifications of LX1990-03 EVAL KIT

• Lead Free Status / RoHS Status: Supplier Unconfirmed

LX1990 E
O
The LX1990 is a dual output current sink
optimized for driving light emitting diodes. The
evaluation board demonstrates how this low cost
bipolar IC enables precise current regulation in
LED display lighting applications, yet requires far
fewer parts than discrete solutions.
The evaluation board ships with two strings of
three LED’s each. Two green and one blue
connected in series to each output. Each LED
has a parallel connected jumper (JB2-JB7) that
allow the LED to be bypassed to remove it from
the circuit so various combinations of LED’s can
be easily configured for each series string. A
small rheostat (R1) in series with R2 (4.32K
which sets the maximum current at 30mA)
varies the R
LED current will vary from about 5mA to 30mA.
Two other jumpers are included, JB1 which
enables the LX1990, and JB8 to which allows an
externally supplied PWM signal to toggle the
R
Evaluation Board Features
Copyright © 2002
Rev. 0.1a, 4/9/02
SET
VERVIEW
ENABLE
VLOAD
Input
PWM
GND
VDD
resistance to allow duty cycle dimming.
Easily configured with 1 to 3 LED’s on
each output
Included rheostat allows output current to
be set from 5 to 30mA
Jumpers allow external PWM signal to
burst dim the LED’s and an external
enable control
SET
VALUATION
Allowable Range
resistance such that the output
2.7 to 5.5V
0 to VDD
0 to VDD
2 to 10V
0V
B
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: [phone]
OARD
Table 1 – Evaluation Board Connections
LX1990 power supply. Quiescent current draw is between 1.4 and
4mA depending on voltage and temperature
LED voltage supply. Required voltage depends on forward voltage
requirements of LED’s and 100-400mV chip overhead
Input for external enable control, board ships with 100K pull-up to
VDD
Input to allow duty cycle dimming of output 150hz to 20Khz logic
signal, active high
Common ground reference
Integrated Products
Microsemi
E
The evaluation board has four possible inputs of
which at least two must be used to operate the
circuit. These inputs are described in table 1
below.
input supply voltage (VDD) in the range of 2.7 to
5.5V. When using all three LED’s in series a
supply voltage of greater than 5.5V is required
on the VLOAD input, since the combined
forward voltage of the three LED’s at the rated
current of 20mA is about 8.4V. However if you
were to bypass as an example the two blue
LED’s by moving up the shorting blocks on JB4
and JB7 then a single 5V supply could be
connected at both VDD and VLOAD to drive the
remaining
blue LED’s since both require a forward voltage
of about 4V. If you are willing to drive the blue
LED’s at only 5mA then voltages as low as 3.3V
will directly drive both the chip and the LED’s.
The other two inputs PWM and ENABLE allow
external control over dimming and shutdown.
The evaluation board comes with a built in 100K
pull-up resistor R3 that is connected between
the ENABLE input and VDD. R3 will enable the
outputs unless JB1 is set to OFF. When JB1 is
in the EXT/ON position enable is also connected
to the external ENABLE input TP5. An external
voltage signal or open collector logic can be
applied to this point to disable the device. This
external signal must be able to drive the 100K
pull-up resistor low (less than 0.8V).
The LX1990 integrated circuit itself requires a
VALUATION
Description
four LED’s
B
OARD
O
PERATION
or conversely the two
U
SER
G
UIDE
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