LX1970 EVALUATION BOARD
USER’S GUIDE
LX1970 VISIBLE LIGHT SENSOR
INTEGRATED PRODUCTS
LX1970 EVALUATION BOARD USER GUIDE
Copyright © 2002 Microsemi Page 2
Rev. 1.1 9/23/03 Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
TABLE OF CONTENTS
Overview .....................................................................................................................................................................3
Features
Operation
T
ABLES
Evaluation Board Connections ..............................................................................................................4
Jumper Explanation.................................................................................................................................4
Test Point Descriptions...........................................................................................................................4
FIGURES
LX1970 Evaluation Board Component List............................................................................................5
LX1970 Evaluation Board Silk Screen & PCB Traces...........................................................................5
LX1970 Evaluation Board Schematic.....................................................................................................6
LX1970 EVALUATION BOARD USER GUIDE
Copyright © 2002 Microsemi Page 3
Rev. 1.1 9/23/03 Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
OVERVIEW
The LX1970 is a new technology light sensor
with spectral response that emulates the human
eye. This device is ideal for monitoring ambient
light for brightness control systems in flat panel
displays. It has a unique photo diode
arrangement (patents pending) with a peak
response at 540nm while sharply attenuating
both ultra violet and infrared wavelengths
without the use of an optical filter. The photo
sensor is a pin diode array with an accurate,
linear, and very repeatable current transfer
function.
The evaluation board ships with an aperture
wheel that allows the user to approximate the
sensor’s mounting inside an assembly with a
entrance hole for light. The aperture wheel can
rotate to program various holes sizes. Three
small rheostats and four input connection
terminals permit the sensor’s output gain
(current to voltage conversion) and dimming
transfer function to be adjusted to the user’s
ambient light conditions, and output voltage
requirements.
For a quick demonstration of the dimming
capability of the sensor the evaluation board can
be configured (by setting J1 to the LED Driver
position, and J4 to the Driver position) to power
two white LED’s by a Microsemi LX1990 LED
sink driver controller (included) when 3 to 5V is
connected across VDD and GND terminals.
Evaluation Board Features
• Aperture wheel allows simulation of
sensor mounting inside a case
• Included rheostats allows easy output
voltage gain conversion for light level
• Additional jumpers enable isolation, and
pull-down diodes for some configurations
• Included LX1990 Sink LED Driver and two
Microsemi white LED’s demonstrate the
sensors utility and ease of use
E
VALUATION BOARD OPERATION
The evaluation board has five possible inputs of
which at least two must be used to operate the
circuit. In the simplest configuration connect 2V
to 5V across VDD and GND. With this power
connected and all jumpers in their open position
(see evaluation board schematic figure 2) the
LX1970 by itself can be evaluated. The SRC
and SNK outputs will act as a current source
and sink respectively and change with the
intensity of light. The output compliance range
will of course depend on the input voltage and
output current (see LX1970 datasheet for
details).
If the light sensors current outputs are to be
used directly, then the SRC and SNK terminals
can be used to hook up external circuitry to the
sensor. If however the application requires
conversion of the output currents to a scalable
voltage output, then J2 and/or J4 should be
used. Jumper J2 when set to the DIVIDER
position connects the SCR output to external
resistors. When jumper J4 is connected in the
SNK PULL-UP position then the SNK output
current can be pulled up to VDD or some lower
external voltage. Jumper J3 when in the D2 IN
position inserts an isolation diode in series with
the divider string for applications where the
sensor may be disengaged for full manual
override. This could be true if power to the
sensors is interrupted, or the SCR diode pull-
down terminal is set low shunting the sensors
output current.
The SCR ADJUST PULL-UP terminal allows an
external DC voltage or PWM signal to connect to
the high side of the voltage divider R1+R2 and
R4+R5. Rheostats R1 and R4 allow easy
adjustment of the divider; they are set to their
maximum (100KΩ) when set fully clockwise.
The SRC FIXED PULL-UP terminal provides a
second input for a DC voltage or PWM signal for
more complex signal conditioning circuits. The
terminal labeled SRC DIODE PULL-DOWN can
be used as described above to shunt the
sensors current; this too could be a DC voltage
or PWM signal.
On the SNK side the evaluation board includes
one 100KΩ rheostat, R6 that can be connected
to VDD to generate a signal inverted from the
SCR output side. On both the SRC and SNK
output a 1uf capacitor (C1 & C3) is placed in
parallel with the output resistors. The capacitors
slow down the response time of the sensor so it
won’t try to track the 50-60Hz lighting. All
evaluation board input connections; jumpers and
test points are summarized in table 1-3 on the
following page. See LX1970 datasheet for
application schematics and suggestions.
LX1970 EVALUATION BOARD USER GUIDE
Copyright © 2002 Microsemi Page 4
Rev. 1.1 9/23/03 Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Input Allowable Range Description
VDD 2 to 5.5V
LX1970 power supply if J1 is set to LX1970 only, or LX1970 power
supply and LX1990 and external LED’s power supply if J1 is
connected to LED DRIVER (LED’s will only light if J4 is also in
DRIVER position.
GND 0V Common ground reference
SRC
Diode
Pull-down
5V to GND, fixed
DC voltage or
PWM/Logic signal
This diode connection is generally used to shunt SRC output current
when disengaging the sensor in a full manual mode
SRC
Adjust
Pull-up
5V to GND, fixed
DC voltage or
PWM/Logic signal
First pull-up connection is generally used to set a minimum output
voltage or adjust output transfer slope for SRC pin
SRC
Fixed
Pull-up
5V to GND, fixed
DC voltage or
PWM/Logic signal
Second pull-up connection is generally used to set a minimum
output voltage or adjust output transfer slope for SRC pin
SNK Pull-
up
5V to GND, fixed
DC voltage or
PWM/Logic signal
This pull-up connection is generally used to set a maximum output
voltage or adjust output transfer slope for SNK pin
Table 1 – Evaluation Board Terminals
Jumper Function
J1
Jumper to LED Driver connects LX1990 driver IC & LX1970 to VDD, Jumper to LX1970
only connects VDD to the LX1970 sensor only.
J2
Jumper to SRC open disconnects external divider circuitry from LX1970 SCR pin. Jumper
to DIVIDER connects external divider circuitry to SRC pin.
J3 Shorts or leaves connect the series diode D2 from SRC pull-down path
J4
Jumper to DRIVER connects the SNK output to the ISET input of the LX1990 through a
4.12K resistor. Jumper to SNK Pull-up connects the SNK pin to the SNK Pull-up external
board connection
Table 2 – Jumper Explanation
Test Point Description
GND Common Ground Reference
VDD VDD Input to LX1970 (2 to 5.5V)
SNK LX1970 SNK output
SRC LX1970 SRC output
SRC Diode
Pull-down
Cathode of diode connected to SRC pin
SRC Adjust
Pull-up
100K rheostat and series 10K resistor to SRC
SRC Fixed
Pull-up
50K series resistor to SRC
SNK Pull-up
100K rheostat and parallel 1µF capacitor to SNK
Table 3 – Terminal/Test Point Descriptions
LX1970 EVALUATION BOARD USER GUIDE
Copyright © 2002 Microsemi Page 5
Rev. 1.1 9/23/03 Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
LX1970 EVALUATION BOARD COMPONENT LIST
MISCELLANEOUS COMPONENTS
Part Description Manufacturer & Part #
Reference
Designators
Qty
IC, Sensor MICROSEMI LX1970ILM
U1
1
IC, Controller
M
ICROSEMI LX1990I
U2
1
Diodes VARIOUS 1N4148
D1,D2
2
LEDs, WHITE Bright
Microsemi UPWLED470A
Optomite or equivalent
LED1 , LED2
2
Terminals/Probe Standoffs
Various
9
CAPACITORS
Part Description Manufacturer & Part #
Reference
Designators
Qty
Capacitor, X7R, 100nF, 50V, 10% Any
C2
1
Capacitor, X7R, 1uF, 50V, 10% Any
C1, C2
2
RESISTORS
Part Description Manufacturer & Part #
Reference
Designators
Qty
Resistor, Pot Thumbwheel 100K Any
R1,R2,R6
3
Resistor, 4.12K, 1%, 1/16W Any
R7
1
Resistor, 10K, 1%, 1/16W Any
R1,R5
2
Resistor, 50.0K, 1%, 1/16W Any
R3
1
LX1970 EVALUATION BOARD SILKSCREEN & PCB TRACES
BOTTOM
SRC
ADJUST
LED-UPW
LX1990
ADJUST
SRC TOP
LED DRIVER
LIGHT
SENSOR
LX1970
0.8MM
1.0MM
1.2MM
1.5MM
1.75MM
2.0MM
D2 OUT
D2 IN
LX1970 ONLY
DIVIDER
SRC
OPEN
2.5MM
DARK
2
ADJUST
SNK
2
2
EVALUATION BOARD
LX1970
(800) 877-6458
MICROSEMI
PULL-UP
DRIVER
SNK
APERTURE'S
U2
SNK
GND0
VDD
J1
C2
LED2
LED1
J4
R7
R5 C3
R4
2
DARK
2.5MM
OPEN
SRC
DIVIDER
LX1970 ONLY
D2 IN
D2 OUT
2.0MM
1.75MM
1.5MM
1.2MM
1.0MM
0.8MM
LX1970
SENSOR
LIGHT
LED DRIVER
SRC TOP
ADJUST
LX1990
LED-UPW
ADJUST
SRC
BOTTOM
DIODE
PULL
DOWN
R6
2
SNK
ADJUST
2
DARK
2.5MM
OPEN
SRC
DIVIDER
LX1970 ONLY
D2 IN
D2 OUT
2.0MM
1.75MM
1.5MM
1.2MM
1.0MM
0.8MM
LX1970
SENSOR
LIGHT
LED DRIVER
SRC TOP
ADJUST
LX1990
LED-UPW
ADJUST
SRC
BOTTOM
SNK PULL-UP
C1
SRC0
D2
SRC
J2
D1
J3
GND
SRC FIXED
U1
R3
R2
R1
2
2
SNK
ADJUST
2
DARK
2.5MM
OPEN
SRC
DIVIDER
LX1970 ONLY
D2 IN
D2 OUT
2.0MM
1.75MM
1.5MM
1.2MM
1.0MM
0.8MM
LX1970
SENSOR
LIGHT
LED DRIVER
SRC TOP
ADJUST
LX1990
LED-UPW
ADJUST
SRC
BOTTOM
SRC ADJ.
BOTTOM
SRC
ADJUST
LED-UPW
LX1990
ADJUST
SRC TOP
LED DRIVER
LIGHT
SENSOR
LX1970
D2 OUT
D2 IN
LX1970 ONLY
DIVIDER
SRC
OPEN
2
ADJUST
SNK
2
2
EVALUATION BOARD
LX1970
(800) 877-6458
MICROSEMI
PULL-UP
DRIVER
SNK
APERTURE'S
U2
SNK
GND0
VDD
J1
C2
LED2
LED1
J4
R7
R5 C3
R4
2
OPEN
SRC
DIVIDER
LX1970 ONLY
D2 IN
D2 OUT
LX1970
SENSOR
LIGHT
LED DRIVER
SRC TOP
ADJUST
LX1990
LED-UPW
ADJUST
SRC
BOTTOM
DIODE
PULL
DOWN
R6
2
SNK
ADJUST
2
OPEN
SRC
DIVIDER
LX1970 ONLY
D2 IN
D2 OUT
LX1970
SENSOR
LIGHT
LED DRIVER
SRC TOP
ADJUST
LX1990
LED-UPW
ADJUST
SRC
BOTTOM
SNK PULL-UP
C1
SRC0
D2
SRC
J2
D1
J3
GND
SRC FIXED
U1
R3
R2
R1
2
2
SNK
ADJUST
2
OPEN
SRC
DIVIDER
LX1970 ONLY
D2 IN
D2 OUT
LX1970
SENSOR
LIGHT
LED DRIVER
SRC TOP
ADJUST
LX1990
LED-UPW
ADJUST
SRC
BOTTOM
SRC ADJ.
BATTERY
GND
BLK
VDD
RED
SGE3010 X
Figure 1
LX1970 EVALUATION BOARD USER GUIDE
Copyright © 2002 Microsemi Page 6
Rev. 1.1 9/23/03 Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
LX1970 EVALUATION BOARD SCHEMATIC
VDD
GND
LX197xIDU
R3 50K
R5
10.0K
SNK Adjust
R6 100K
C1
1.0F
N/C
VDD
N/C
SRC
GND
N/C
N/C
SNK
1
2
3
4
5
6
7
8
D1 IN4148
D2
1N4148
SRC
Bottom
Adjust
R 4 100K
R2 10.0K
SRC Top
Adjust
R1 100K
GND
SNK
SNK Pull-up
SRC Adj Pull-up
SRC Fixed Pull-up
SRC Diode Pull-down
D2 In
D2 Out
C3
1.0F
J2
J1
J4
R7
4.12K
ISET
GND I
OUTA
I
OUTB
VDD
ENA
LX1990ILM
SRC
2
1
3
6
4
5
J3
C4
0.1F
Driver
SNK Pull-up
SRC open
Divider
LX1970 only
LED Driver
LED1
LED2
Figure 2 – Schematic
/