Microsemi LX1970 User Manual

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LX1970 EVALUATION BOARD USER’S GUIDE

LX1970 VISIBLE LIGHT SENSOR

INTEGRATED PRODUCTS

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LX1970 EVALUATION BOARD USER GUIDE

TABLE OF CONTENTS

Overview.....................................................................................................................................................................3

Features Operation

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

Rev. 1.1 9/23/03 Integrated Products

11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570

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LX1970 EVALUATION BOARD USER GUIDE

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

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 pulldown 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.

Rev. 1.1 9/23/03 Integrated Products

11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570

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LX1970 EVALUATION BOARD USER GUIDE

Input Allowable Range Description

LX1970 power supply if J1 is set to LX1970 only, or LX1970 power

VDD 2 to 5.5V

GND 0V Common ground reference SRC

Diode

Pull-down

SRC

Adjust

Pull-up

SRC

Fixed

Pull-up

SNK Pull-

5V to GND, fixed DC voltage or PWM/Logic signal 5V to GND, fixed DC voltage or PWM/Logic signal 5V to GND, fixed DC voltage or PWM/Logic signal 5V to GND, fixed DC voltage or PWM/Logic signal

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.

This diode connection is generally used to shunt SRC output current

First pull-up connection is generally used to set a minimum output

This pull-up connection is generally used to set a maximum output

Table 1 – Evaluation Board Terminals

when disengaging the sensor in a full manual mode

voltage or adjust output transfer slope for SRC pin

Second pull-up connection is generally used to set a minimum

output voltage or adjust output transfer slope for SRC pin

voltage or adjust output transfer slope for SNK pin

Jumper Function

J3 Shorts or leaves connect the series diode D2 from SRC pull-down path

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

SRC Adjust

Pull-up

SRC Fixed

Pull-up

SNK Pull-up

Jumper to LED Driver connects LX1990 driver IC & LX1970 to VDD, Jumper to LX1970 only connects VDD to the LX1970 sensor only. Jumper to SRC open disconnects external divider circuitry from LX1970 SCR pin. Jumper to DIVIDER connects external divider circuitry to SRC pin.

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

Cathode of diode connected to SRC pin 100K rheostat and series 10K resistor to SRC 50K series resistor to SRC

100K rheostat and parallel 1µF capacitor to SNK

Rev. 1.1 9/23/03 Integrated Products

11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570

Table 3 – Terminal/Test Point Descriptions

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LX1970 EVALUATION BOARD USER GUIDE

IC, Sensor MICROSEMI LX1970ILM

IC, Controller Diodes VARIOUS 1N4148

LEDs, WHITE Bright

Terminals/Probe Standoffs

Capacitor, X7R, 100nF, 50V, 10% Any Capacitor, X7R, 1uF, 50V, 10% Any

Resistor, Pot Thumbwheel 100K Any Resistor, 4.12K, 1%, 1/16W Any Resistor, 10K, 1%, 1/16W Any Resistor, 50.0K, 1%, 1/16W Any

DIODE

SRC TOP

SRC TOP ADJUST

ADJUST

LX1970 EVALUATION BOARD SILKSCREEN & PCB TRACES

SRC

SRC0 PULL

DOWN

LX1970

SENSOR

GND

APERTURE'S

SRC ADJ.

LX1970 EVALUATION BOARD COMPONENT LIST

MISCELLANEOUS COMPONENTS

Part Description Manufacturer & Part #

ICROSEMI LX1990I

Microsemi UPWLED470A

Optomite or equivalent

CAPACITORS

Part Description Manufacturer & Part #

RESISTORS

Part Description Manufacturer & Part #

VDD

LX1970 ONLY

LED DRIVER

MICROSEMI

1.75MM

2.0MM

DARK

LX1970

R5 C3

0.8MM

SRC

BOTTOM

ADJUST

1.5MM

1.0MM

1.2MM

SNK PULL-UP

SNK

ADJUST

GND0

LX1990

LED-UPW

PULL-UP

LED2

LED1

DRIVER

SNK

Figure 1

SRC

OPEN

DIVIDER

D2 OUT

LIGHT

SENSOR

D2 IN

SRC0

DIODE

PULL DOWN

GND

LX1970

APERTURE'S

SRC TOP

ADJUST

SRC ADJ.

SRC FIXED

OPEN

D2 OUT

LIGHT

DIVIDER

D2 IN

SRC FIXED

SRC

(800) 877-6458

2.5MM

EVALUATION BOARD

Reference

Designators

D1,D2

LED1 , LED2

Various

Reference

Designators

C1, C2

Reference

Designators

R1,R2,R6

R1,R5

VDD

LX1970 ONLY

LED DRIVER

MICROSEMI

(800) 877-6458

EVALUATION BOARD

R5 C3

BATTERY

LX1970

SRC

BOTTOM

ADJUST

VDD

RED

SNK

ADJUST

SNK PULL-UP

GND0

LX1990

GND

BLK

LED-UPW

SNK

PULL-UP

Qty

1 2

Qty

1 2

Qty

3 1 2 1

LED2

LED1

DRIVER

SNK

SGE3010 X

Rev. 1.1 9/23/03 Integrated Products

11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570

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LX1970 EVALUATION BOARD USER GUIDE

VDD

GND

LX197xIDU

R3 50K

10.0K

SNK Adjus t R6 100K

1.0F

N/C

VDD

N/C

SRC

GND

N/C

SNK

D1 I N 4148

1N4148

SRC Bottom Adjust R 4 100K

R2 10. 0K

SRC Top Adjust R1 100K

GND

SNK

SNK Pul l-up

SRC Adj Pull-up SRC Fixed Pull-u p

SRC Diode Pull-down

D2 In

D2 Out

1.0F

4.12K

ISET

GND I

OUTA

OUTB

VDD

ENA

LX1990ILM

SRC

0.1F

Driver

SNK Pull-up

SRC open

Divider

LX1970 only

LED D riv er

LED1

LED2

LX1970 EVALUATION BOARD SCHEMATIC

Rev. 1.1 9/23/03 Integrated Products

Figure 2 – Schematic

11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570