LX1991 EVALUATION BOARD
USER’S GUIDE
LX1991 Six Output Programmable LED Current Sink
I N T E G R A T E D
P R O D U C T S
LX1991 E
VALUATION
B
OARD
U
SER
G
UIDE
T
ABLE
O
F
C
ONTENTS
Overview
.....................................................................................................................................................................3
Features
Operation
T
ABLES
Evaluation Board Connections .............................................................................................................. 3
Jumper Explanation................................................................................................................................. 4
Test Point Descriptions........................................................................................................................... 4
F
IGURES
LX1991 Evaluation Board Component List............................................................................................ 5
LX1991 Evaluation Board Silk Screen.................................................................................................... 5
LX1991 Evaluation Board Schematic ..................................................................................................... 6
Copyright © 2002
Rev. 1.0 1/8/03
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 2
LX1991 E
VALUATION
B
OARD
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O
VERVIEW
The LX1991 six channel current sink driver is
ideal for controlling brightness of high quality
dimmable LED’s. 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 six (Microsemi
UBLED470A)
white surface mount LED’s whose
cathodes are connected to each sink output of
the LX1991. The anodes of the LED’s are
connected together to a test point called VLOAD
which the user can connect to an external
voltage source (typically 5V, maximum is 40V)
LED6 requires an external jumper between TP7
and TP8 to allow current to flow.
This
demonstrates that one or more channels can be
left open without effecting the other channels. In
addition these test points allow the easy addition
of a application specific load or a current probe
loop. Use of a current probe will allow easy
viewing of the current rise and fall times.
A small rheostat (Current Adjust) in series with
R8 (1.02K which sets the maximum current at
30mA) varies the R
SET
resistance such that the
output LED currents will vary from about 1.5mA
to 30mA. Two other jumpers are included,
EXT_EN which enables/disables the LX1991,
and PWM_IN which allows an externally
supplied PWM signal to toggle the DIG_DIM
input to allow duty cycle dimming.
Evaluation Board Features
•
•
•
One channel is left open for application
specific loads to be added or current
probe loop
Included rheostat allows output current to
be set from 1 to 30mA
Jumpers allow external PWM signal to
burst dim the LED’s and an external
enable control
E
VALUATION
B
OARD
O
PERATION
The evaluation board has four possible inputs of
which at least two must be used to operate the
circuit. In the simplest configuration connect 5V
to both EXT VDD and VLOAD and the common
(ground return) to RTN. With power connected
to these two pins and the a jumper (factory
installed) between PWM_IN and PULL-UP the
evaluation board should be operational. The
LX1991 integrated circuit itself requires a input
supply voltage (EXT VDD) in the range of 4.5 to
5.5V. When using the included white LED’s a
supply voltage of at least 4V is required on the
VLOAD input depending on the current setting
(current adjust). All inputs are described in table
1 below.
The other two inputs PWM_IN and ENABLE
allow external control over dimming and
shutdown. The evaluation board comes with a
built in 10K pull-up resistor R1 that is connected
between the ENABLE input and EXT VDD. R1
will enable the device unless a jumper is placed
between
EXT_EN
and
RTN
(GND).
Input
EXT VDD
Allowable Range
4.5 to 5.5V
Description
LX1991 power supply. Quiescent current draw is between 4 and
13mA depending on voltage and temperature and the programmed
output sink currents
LED voltage supply. Required voltage depends on forward voltage
requirements of LED’s and 700-1000mV chip overhead. This
current will vary between 9 and 180mA depending on the
programmed output sink current and if all six LED are connected.
Input for external enable control, board ships with 10K pull-up to
EXT VDD
Input to allow duty cycle dimming of output 150hz to 100Khz logic
signal, active high
Common ground reference
VLOAD
3 to 40V (5V typ.)
EXT_EN
PWM_IN
RTN/GND
0 to VDD
0 to VDD
0V
Table 1
– Evaluation Board Connections
Copyright © 2002
Rev. 1.0 1/8/03
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 3
LX1991 E
VALUATION
B
OARD
U
SER
G
UIDE
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 10K pull-up resistor low (less than
0.8V).The PWM_IN header input allows an
external PWM signal to control the output
current by duty cycle dimming. This is
accomplished by switching the device’s
DIG_DIM input with a logic signal.
The
practical limit to this switching frequency is
about 100Khz, at frequencies greater than this
internal delays will add errors to the expected
output duty cycle. The evaluation board comes
with a 470pF CSLOPE capacitor. This value
can be increased to vary the rise and fall times
of the output current waveform. For greater
detail see the LX1991 datasheet.
Test Points SINK1 to SINK6 allow you to
monitor the voltage drop across these pins to
ground. This voltage will change to maintain the
correct forward voltage across the LED’s for the
programmed sink current. It can range from as
low as 400mV to 40V when the outputs are off
depending on the VLOAD supply voltage.
The various jumper positions are summarized in
table 2 and test points in table 3. The factory
installed active and passive components list can
be found in table 4. Following the two tables
you will find the PCB silkscreen figure 1 and the
circuit schematic in figure 2. All necessary PCB
traces and components are on the topside of the
board. However there are PCB traces and
silkscreen on the bottom side that when
populated is used for a special version of the
evaluation board that is used internally by
Microsemi for training and demonstration
purposes.
Jumper
PWM_IN
EXT_EN
Function
Jumper to PULLUP connects PWM_IN through a 10K pull-up resistor to EXT VDD, Jumper
to RTN connects PWM_IN to Ground. Open allows hookup to external PWM source.
Jumper to RTN disables the LX1991 by pulling down on the 10K pull-up resistor ; EXT_EN
open enable the LX1991 through the 10K pull-up to EXT VDD
Table 2
– Jumper Explanation
Test
Point
VLOAD
RTN/GND
EXT VDD
EXT_EN
SINK1
SINK2
SINK3
SINK4
SINK5
SINK6
PWM_IN
Description
VLOAD Input, power supply to LED’s (3 to 40V)
Common Ground Reference
VDD Input to LX1991 (4.5 to 5.5V)
ENABLE input can be connected to external enable signal; high or floating is on, low is
off (LX1991 pin 16)
SINK1 (LX1991 pin 3)
SINK2 (LX1991 pin 4)
SINK3 (LX1991 pin 6)
SINK4 (LX1991 pin 7)
SINK5 (LX1991 pin 8)
SINK6 (LX1991 pin 10)
PWM Input can be connected to external pulse generator for duty cycle dimming
(LX1991 pin 1)
Table 3
– Test Point Descriptions
Copyright © 2002
Rev. 1.0 1/8/03
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 4
LX1991 E
VALUATION
B
OARD
U
SER
G
UIDE
LX1991 EVALUATION BOARD COMPONENT LIST
MISCELLANEOUS COMPONENTS
Part Description
IC, Controller
LEDs, BLUE Bright
Probe Standoffs
Manufacturer & Part #
M
ICROSEMI
LX1991ILM
Microsemi
UBLED470A
Optomite or equivalent
Reference
Designators
U1
LED1 - LED6
Various
Qty
1
6
8
CAPACITORS
Part Description
Capacitor, X7R, 100nF, 50V, 10%
Capacitor, CGO, 470pF,
Manufacturer & Part #
Any
Any
RESISTORS
Reference
Designators
C3, C4
CSLOPE
Qty
2
1
Part Description
Resistor, Pot Thumbwheel 20K
Resistor, 1.02K, 1%, 1/16W
Resistor, 10K, 1%, 1/16W
Not Used
Manufacturer & Part #
Any
Any
Any
n/a
Reference
Designators
Current Adjust
R8
R1,R6
R7
Qty
1
1
2
0
LX1991 EVALUATION BOARD SILKSCREEN
RTN
LX EV L
1991 A
V oad
l
TP8
GN
D
LED 4
L E D 5 LED
6
LED
2
SIN
K2
SIN
K1
PU
LL
U
P
SIN
K6
SIN
K5
SIN
K3
R7
TP7
LED
1
LED
3
C
3
PW
M
IN
RTN
U
1
RTN
EXTV
DD
SIN
K4
U1
R1
R8
R6
C PE
SLO
C r ent A
ur
djust
GND
1
RTN
EXT_
EN
LX1991SIXO
UTPUTPROGRA M B LEDC
M A LE
URREN
T
SIN EV LUA NBO RD
K A TIO A
Sil kscr een Top RR
Figure 1
Copyright © 2002
Rev. 1.0 1/8/03
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
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