LED Backlight Controller for LCD Monitors by General Digital by armyboy666

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									   Overview
                           LED BACKLIGHT CONTROLLER
                           General Digital’s™ microprocessor-based LED Backlight
                           Controller has been designed to support LCD Monitor
LED BACKLIGHT CONTROLLER

                           applications that require sunlight readability, as well as
                           night time vision (NVIS) performance. This controller is
                           optimally designed to drive up to four (4) LED rails (up to
                           two sunlight readable rails and up to two NVIS rails). The
                           controller will operate from +12 Vdc to +34 Vdc and
                           drives LEDs up to 10 amps in sunlight readable mode, and
                           3 amps in NVIS mode. The maximum and minimum
                           brightness for each mode of operation (sunlight readable/
                           NVIS) is programmable. The controller allows brightness
                           control from full off to full brightness in both modes of
                           operation, providing 256 steps and more than 1000:1 dim-
                           ming. It accepts both push button brightness control via a
                           membrane switch or mechanical buttons (Fig. 4) or a 10K                                                         can threaten the health of the LCD and/or other monitor
                           analog potentiometer (Fig. 5). In sunlight mode, the max-                                                       electronics. When the rail temperature exceeds a predeter-
                           imum current is monitored and controlled to prevent                                                             mined “over temperature” limit, the controller automati-
                           “thermal runaway” under extreme temperature condi-                                                              cally reduces the backlight brightness (e.g. 80%) to reduce
                           tions, assuring long life for the LEDs. Operators may select                                                    power consumption, which in turn, will reduce the amount
                           between sunlight mode and NVIS mode via a two-pin                                                               of heat generated. If the temperature continues to rise and
                           input from a mechanical switch or TTL signal.                                                                   reaches a successive limit threshold, then the backlight
                                                                                                                                           brightness is further reduced. In the event that the rail
                           OVER TEMPERATURE ALGORITHM                                                                                      temperature reported exceeds a final limit, the backlight is
                           Our microprocessor-driven LED controller is configured to                                                        turned off completely. The backlight brightness will be
                           communicate with a pair of temperature sensors (thermis-
                           tors). This ability enables our controller to monitor the
                           temperature of our LED Backlight rails. The LED control-
                           ler’s firmware can be programmed to respond to “over
                           temperature” conditions that can result from failure of the
                           monitor’s electronics (e.g., fans), operator error (e.g.,
                           blocked fan airflow), or environmental conditions (e.g., air
                           conditioning failure, solar radiation or extreme heat) that




                                                                                                                              Serial Layout

                                                                                                                                Figure 1




                                                                                                                         Serial-Parallel Layout

                                                                                                                                Figure 2
        Page 1 of 6




                                                                    General Digital ™ Corporation 8 Nutmeg Road South South Windsor, CT 06074 Toll-Free Phone: 800.952.2535
                                                                    Local: (860) 282-2900 Fax: (860) 282-2244 E-mail: gd_ds@GeneralDigital.com Web Site: www.GeneralDigital.com
                           Specifications subject to change without notice or obligation. Trademarks are the property of their respective owners.                                            February 2010
   Overview
                           LED BACKLIGHT CONTROLLER
                           restored to various brightness levels as the rail tempera-                                                      ple LED failures will not render the monitor inoperable,
                           ture returns to normal operating levels (Fig. 3). Since Gen-                                                    and in most cases will still provide a very uniform back-
LED BACKLIGHT CONTROLLER

                           eral Digital has control of the firmware, customers can                                                          light. This non-catastrophic failure condition is essential
                           define the number of temperature limits, their associated                                                        for mission critical applications. It should also be noted
                           temperatures, the brightness reduction required at each                                                         that our LED Controller can support up to 10 amps of
                           level and the clearing temperatures. The default firmware                                                        output current. This is far greater than typical current
                           provides three over-temperature limits with brightness                                                          regulated LED module drivers, which only support 1 amp
                           reduction values of 80%, 60% and off, respectively.                                                             per module. Prior to the advent of our LED controller, our
                                                                                                                                           typical sunlight/NVIS backlight for 19" display required
                           BRIGHTNESS CONTROL                                                                                              six LED modules to drive our LED rails. Substituting our
                           A unique feature of the General Digital’s LED Backlight                                                         LED Controller saved considerable expense, mechanical
                           Controller PCB is an interface to support a pair of bright-                                                     space and weight. Furthermore, our controller eliminated
                           ness sensors (I2C). Feedback from the optical sensor allows                                                     the need for technician time to calibrate each of the indi-
                           the controller to maintain a constant backlight brightness                                                      vidual modules, providing further cost savings.
                           even when the ambient temperatures vary drastically.
                           This greatly improves functionality since the current                                                           PROGRAMMABILITY
                           draw and brightness of the LED is directly influenced by                                                         The performance of the LED controller is programmable
                           its temperature.                                                                                                at the factory to meet the specific requirements of each
                                                                                                                                           application. The following parameters are programmable:
                           CONVENTIONAL DESIGNS                                                                                                Maximum / Minimum Brightness of Sunlight Readable
                           Most commercial LED rails for LCD displays are designed                                                             LED Rails
                           to be driven serially (Fig. 1). The primary advantage of
                                                                                                                                               Maximum / Minimum Brightness of NVIS LED Rails
                           this design approach is that the associated controller
                                                                                                                                               Current Limiting of Sunlight Readable & NVIS
                           requires only a very low output current. Typically, the
                                                                                                                                               LED Rails
                           controllers occupy a small footprint since the low output
                           override requires only small traces. However, the glaring                                                            » Monitor Maximum Output of Sunlight Readable
                                                                                                                                                  Rails to Prevent Thermal Runaway Under Extreme
                           disadvantage of a serial driven LED rail, and associated
                                                                                                                                                  Thermal Environments
                           controller, is that there is no soft failure mechanism in the
                           event of an individual LED failure. A failure of a single                                                            » Ensures Long Life of LEDs
                           LED will render the entire rail inoperable. The other disad-                                                        Define Brightness of Sunlight Readable and NVIS
                           vantage is that the LED controller will produce a very high                                                         Modes When Switching Modes
                           output voltage (100 Vdc typical), which constitutes a haz-                                                           » Brightness Algorithm Choices
                           ardous voltage and complicates its integration.
                                                                                                                                                    • Default Brightness (value defined by user)

                           OUR DESIGN                                                                                                               • Last Brightness (recalls last setting)
                           General Digital’s™ LED backlight designs are designed to                                                                 • Based on Potentiometer Position
                           provide a very low cost of ownership by ensuring extended
                                                                                                                                                    • Custom
                           operational life of the LEDs. Our LED rails use a serial-
                           parallel design philosophy, whereby we drive groupings of                                                           Define “Over Temperature” Brightness Reduction
                                                                                                                                               Parameters (can be disabled)
                           multiple LEDs. However, what differentiates our design
                           approach from other’s is that each of the LED groupings is                                                           » Number of Over Temperature Limits
                           driven in a parallel manner (Fig. 2). The primary benefit is                                                            (set points)

                           that a single LED failure will only affect its immediate                                                             » Corresponding Temperature Value for Each Limit
                           grouping (soft failure), but will not affect any of the other                                                          (set point)
                           groupings of LEDs. The benefit is that singular or multi-                                                             » Target Backlight Brightness (e.g., 80%) for Each
                                                                                                                                                  Temperature Limit
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                                                                    General Digital ™ Corporation 8 Nutmeg Road South South Windsor, CT 06074 Toll-Free Phone: 800.952.2535
                                                                    Local: (860) 282-2900 Fax: (860) 282-2244 E-mail: gd_ds@GeneralDigital.com Web Site: www.GeneralDigital.com
                           Specifications subject to change without notice or obligation. Trademarks are the property of their respective owners.                                              February 2010
   Overview
                           LED BACKLIGHT CONTROLLER
                                                               FEATURE                                                                                      BENEFIT
                             Support for Brightness Sensors (Up to Two)
LED BACKLIGHT CONTROLLER

                              - One (1) LED Rail – Sunlight Readable (SR) and Night                                         Consistent and Predictable Luminance
                                Vision Imaging System (NVIS)                                                                Sensors provide real-time brightness feedback from the LED backlights to
                                                                                                                            the microprocessor so that the brightness can automatically be corrected for
                                                                                                                            changes due to ambient temperature fluctuations, increased current draw of
                                                                                                                            the LEDs, decay of the LED, etc. Ensures consistent performance from one
                                                                                                                            monitor to another despite inherent component tolerances.


                              - One (1) Ambient Light with Proximity Sensor                                                 Maximizes Backlight Life, Power and Energy Savings
                                                                                                                            Allows for automatic brightness/dimming control of LED backlights based
                                                                                                                            on ambient lighting conditions. Use only as much brightness as the working
                                                                                                                            environment demands. A proximity sensor determines if the optical sensor
                                                                                                                            is obstructed, thereby preventing false readings or unintended brightness
                                                                                                                            adjustments.

                                                                                                                            Custom Brightness Profiles
                                                                                                                            Custom control profiles (firmware) can be created by General Digital for the
                                                                                                                            LED Controller to meet specific customer requirements.


                             Support for Multiple Temperature Sensors

                                 - Embedded on LED Rail                                                                     Prevent Critical Hardware Failures
                                                                                                                            Provides real-time temperature feedback from the LED rails. This data is used
                                                                                                                            by the over-temperature brightness/power control algorithm to automatically
                                                                                                                            reduce backlight power consumption (brightness) in response to excessive
                                                                                                                            temperatures, which reduces heat generation and prevents critical failure of
                                                                                                                            the LCD or associated electronics.


                                 - Other                                                                                    Monitor other critical temperature hot spots within the integrated solution/
                                                                                                                            monitor.


                             Current Limiting for LED Rails (SR and NVIS)                                                   Inherently, LEDs will draw more current as they heat up. After a certain
                                                                                                                            temperature threshold is exceeded, the LEDs power efficiency and brightness
                                                                                                                            will degrade; furthermore, as the LEDs lose brightness, they will continue to
                                                                                                                            draw more current and dissipate more heat.

                                                                                                                            Prevention of Thermal Runaway
                                                                                                                            The LED controller monitors the current to each LED rail and automatically
                                                                                                                            reduces the current if it exceeds a predetermined value that is stored as a
                                                                                                                            constant in the controller’s memory/firmware.

                                                                                                                            Power Efficiency
                                                                                                                            Proactive control of the backlight current prevents the backlights from
                                                                                                                            demanding more power after they have exceeded their optimal luminance
                                                                                                                            threshold.

                                                                                                                            LCD Failure Protection
                                                                                                                            By directly limiting the power consumption of the backlight and indirectly
                                                                                                                            reducing the heat generated, the LED controller prevents over-temperature
                                                                                                                            conditions from developing. If allowed to go unchecked, what could occur is
                                                                                                                            temporary or permanent failure of the liquid crystal material and/or the LCD’s
                                                                                                                            optical films and diffusers.

                                                                                                                            Controlled Brightness Under Extreme Temperature
                                                                                                                            This feature is especially important for applications that have high ambient
                                                                                                                            temperature requirements or that will be mounted in sealed enclosures without
                                                                                                                            active cooling provided.
        Page 3 of 6




                                                                    General Digital ™ Corporation 8 Nutmeg Road South South Windsor, CT 06074 Toll-Free Phone: 800.952.2535
                                                                    Local: (860) 282-2900 Fax: (860) 282-2244 E-mail: gd_ds@GeneralDigital.com Web Site: www.GeneralDigital.com
                           Specifications subject to change without notice or obligation. Trademarks are the property of their respective owners.                                                  February 2010
   Overview
                           LED BACKLIGHT CONTROLLER
                                                               FEATURE                                                                                        BENEFIT
                             Hardware Protection                                                                            Critical Failure Detection
LED BACKLIGHT CONTROLLER

                                                                                                                            In the event that the microprocessor or either of the digital potentiometers
                                                                                                                            fails, the backlights will be intentionally shut off. This will prevent the LEDs
                                                                                                                            from entering a “runaway” thermal condition that could lead to permanent
                                                                                                                            damage of the LCD and its infrastructure.

                             Programability

                              - Automatic Over-Temperature “Soft Failure” Algorithm                                         Critical Failure Protection
                                                                                                                            In response to over-temperature conditions reported within the monitor
                                                                                                                            from an integrated temperature sensor, the controller can be programmed
                                                                                                                            to automatically reduce brightness and power consumption of the LED
                                                                                                                            backlights, thereby reducing internally generated heat. Default code will
                                                                                                                            reduce brightness to 80% at the first over-temperature failure, 60% for the
                                                                                                                            second failure, and will shut off the backights if the third temperature limit is
                                                                                                                            exceeded. Backlights will be turned on and brightness increased as internal
                                                                                                                            temperature decreases below each established temperature limit. Custom
                                                                                                                            firmware can be developed to establish a specific number of temperature
                                                                                                                            limits and the percentage of brightness for each limit.


                              - Minimum/Maximum Sunlight Readable Brightness                                                Consistent and Predictable Luminance
                                                                                                                            The firmware can be configured to ensure that the minimum brightness does
                                                                                                                            not go below a specific luminance, and the maximum brightness does not
                                                                                                                            exceed a specific luminance. The results are more accurate when using the
                                                                                                                            optional brightness sensors.


                              - Minimum/Maximum NVIS Brightness                                                             Consistent and Predictable Luminance
                                                                                                                            The firmware can be configured to ensure that the minimum brightness does
                                                                                                                            not go below a specific luminance, and the maximum brightness does not
                                                                                                                            exceed a specific luminance. The results are more accurate when using the
                                                                                                                            optional brightness sensors.


                              - Current Limits                                                                              Maximizes Backlight Life/Critical Failure Protection
                                                                                                                            Prevents thermal runaway under extreme thermal environment variations and
                                                                                                                            increases LED longevity.


                              - Define Brightness of Sunlight Readable and NVIS                                              Consistent and Predictable Luminance
                                Modes when Switching Between Modes                                                          The brightness can be programmed to be a default brightness (defined
                                                                                                                            by customer), or last brightness (recalls last setting made), based on
                                                                                                                            potentiometer position, or a custom setting.


                             Supports General Digital’s Serial-Parallel LED                                                 Soft Failure Design
                             Backlight Designs                                                                              General Digital’s LED backlight rails utilize a serial-parallel design philosophy
                                                                                                                            that provides applications with a hardware “soft failure” mechanism, which
                                                                                                                            minimizes the risk of a critical failure due to the failure of a single, or multiple,
                                                                                                                            LEDs.
        Page 4 of 6




                                                                    General Digital ™ Corporation 8 Nutmeg Road South South Windsor, CT 06074 Toll-Free Phone: 800.952.2535
                                                                    Local: (860) 282-2900 Fax: (860) 282-2244 E-mail: gd_ds@GeneralDigital.com Web Site: www.GeneralDigital.com
                           Specifications subject to change without notice or obligation. Trademarks are the property of their respective owners.                                                      February 2010
   Overview
                           LED BACKLIGHT CONTROLLER
                           ORDERING/OPTIONS
                           P/N 21-101...Support for Sunlight Readable and NVIS
                           P/N 21-127...Support for Sunlight Readable Only
LED BACKLIGHT CONTROLLER


                           PHYSICAL CHARACTERISTICS
                           Weight:          74.2 grams

                           Size:                                          4.000" x 3.000" x 0.625"                                                  Figure 4

                           PCB Thickness:                                 0.062"

                           Input Connector:                               J1

                           Sunlight Rail Connectors: J2, J3

                           NVIS Rail Connectors:                          J6, J7

                           Brightness Input:                              J4

                           LED Status Connector:                          J5

                           Push Button Input:                             J9
                                                                                                                                                    Figure 5
                           Mode Connector:                                J8

                           Thermistor Input:                              J10, J13

                           Brightness Sensor Input:                       J11, J12




                                                                                                                                                    PWB Layout
                                                                       Figure 3                                                                     Figure 6
        Page 5 of 6




                                                                    General Digital ™ Corporation 8 Nutmeg Road South South Windsor, CT 06074 Toll-Free Phone: 800.952.2535
                                                                    Local: (860) 282-2900 Fax: (860) 282-2244 E-mail: gd_ds@GeneralDigital.com Web Site: www.GeneralDigital.com
                           Specifications subject to change without notice or obligation. Trademarks are the property of their respective owners.                    February 2010
LED BACKLIGHT CONTROLLER




                                                                                                                                                                              LED BACKLIGHT CONTROLLER Specifications
MAXIMUM RATINGS*                                                                                                J5: Video Status I/O Pass Through
 Symbol            Parameter                                   Value                      Unit                  Mating Connector: JST XHP-6
 Vin               Supply Voltage                              1.00 to 20.00              Vdc                        Pin     Signal
 Vsig              Voltage to All Input Pins                    -0.7 to 5.25              Vdc                            1   Video OK Input
 Imax              Input Current                               10                         Adc                            2   Ground
 Pmax              Output power                                138                        Watts                          3   Video Standby Input
 Top               Operating Temperature                       -40 to +75                 C°                             4   Video OK Input
 Tst               Storage Temperature                         -60 to +150                C°                             5   Ground
 *Maximum ratings denote the values beyond which damage will                                                             6   Video Standby Input
occur.

                                                                                                                J6 and J7: NVIS LED Rail Output
RECOMMENDED OPERATING VALUES                                                                                    Mating Connector: Tyco Electronics 640250-2
 Symbol            Parameter                                   Typical Value               Unit                      Pin     Signal
 Vin               Supply Voltage                              12.0 to 15.3                Vdc                           1   + Vout
 Lhigh             Logic Input High                            1.27 to 5.00                Vdc                           2   Ground
 Llow              Logic Input Low                             0 to 0.70                   Vdc
 Din               Dimming Potentiometer                       0 to 5.00                   Vdc                  J8: NVIS Control Input
                                                                                                                Mating Connector: JST XHP-2
CONNECTORS                                                                                                           Pin     Signal
J1: Voltage Input                                                                                                        1   Signal Input High=NVIS Mode
Mating Connector: Tyco Electronics 794617-8                                                                              2   Ground
     Pin         Signal
       1         +12 to 15Vdc                                                                                   J9: Push Button Dimming Input
       2         +12 to 15Vdc                                                                                   Mating Connector: JST XHP-3
       3         +12 to 15Vdc                                                                                        Pin     Operation
       4         +12 to 15Vdc                                                                                            1   Brightness Up Push Button
       5         Ground                                                                                                  2   Brightness Down Push Button
       6         Ground                                                                                                  3   Ground
       7         Ground
       8         Ground                                                                                         J10, J13: Thermistor Input
                                                                                                                Mating Connector: Molex 51021-0200
J2 and J3: Sunlight LED Rail Output                                                                             Thermistor: U.S. Sensor PS10352
Mating Connector: Tyco Electronics 640250-3                                                                          Pin     Signal
     Pin         Signal                                                                                                  1   Thermistor In
       1         + Vout                                                                                                  2   Ground
       2         NC
       3         Ground                                                                                         J11, J12: Brightness Sensor Input
                                                                                                                Use General Digital 21-147
J4: Analog Dimming Input                                                                                             Pin     Signal
Mating Connector: JST XHP-4                                                                                              1   3.3 Vdc
     Pin         Signal                                                                                                  2   Ground
       1         + 5Vdc Output for Potentiometer                                                                         3   A0
       2         Dimming Control Voltage Input                                                                           4   A1
       3         Ground                                                                                                  5   SCL
       4         Ground                                                                                                  6   SDA
                                                                                                                                                                                     Page 6 of 6




                                         General Digital ™ Corporation 8 Nutmeg Road South South Windsor, CT 06074 Toll-Free Phone: 800.952.2535
                                         Local: (860) 282-2900 Fax: (860) 282-2244 E-mail: gd_ds@GeneralDigital.com Web Site: www.GeneralDigital.com
Specifications subject to change without notice or obligation. Trademarks are the property of their respective owners.                                        February 2010

								
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