Led Backlight Controller Ds NoPW

8/4/2019 Led Backlight Controller Ds NoPW

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LED BACKLIGHT CONTROLLER

G e n e r al D i g i t a l™ C o r p o r a t i on 8 N u t m eg R o ad S o u th S o u th W i n d s o r , CT 0 6 0 74 To l l - F r ee P h o n e:8 0 0 . 9 5 2 . 2 5 3 5 : . : . .S p e c i f i c a t i o ns s u b j e ct to c h a n ge w i t h o ut n o t i ce o r o b l i g a t i o n. Tr a d e m a r ks a re t he p r o p e r ty of the ir r e s p e c t i ve o w n e r s . F e b r u a r y 2 0 1

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General Digital’s™ microprocesso r-based LED Backlight

Controller has been designed to support LCD Monitor

applications that require sunlight readabilit y, 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). Thecontroller 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

analog potentiometer (Fig. 5). In sunlight mode, the max-

imum current is monitored and controlled to prevent“thermal runaway ” under extreme temperature condi-

tions, assuring long life for the LEDs. Operators may select

between sunlight mode and NVIS mode via a two-pin

input from a mechanical switch or TTL signal.

OVER TEMPER ATURE ALGORITHM

Our microprocesso r-drive n LED controlle r is configure d to

communicat e wit h a pair of temperatur e sensors (the r mis-

tors). This abilit y enables our controlle r to monito r the

temperatur e of our LED Backlight rails. The LED control-

ler ’s firmwar e can be programme d to respon d to “over temperature ” condition s that can resul t from failure of the

monito r ’s electronic s (e.g., fans), operato r error (e.g.,

blocked fan airflow), or environmenta l condition s (e.g., air

conditionin g failure, solar radiatio n or extrem e heat) that

can threate n the healt h of the LCD and/o r other monitor

electronics . When the rail temperatur e exceeds a predete r

mined “over temperature ” limit, the controlle r automati-cally reduces the backligh t brightnes s (e.g. 80%) to reduce

powe r consumption , whic h in turn, will reduce th

amount of heat generated . If the temperatur e continue s t

rise and reaches a successive limit threshold , then th

backlight brightnes sis furthe r reduced . In the event tha

the rail temperatur e reporte d exceeds a final limit, th

backligh t is turned off completel y. The backligh

brightnes s will be

Serial Layout

Figure 1

Serial-Parallel Layout

Figure 2

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restore d to various brightnes s levels as the rail tempera-

ture returns to normal operatin g levels (Fig. 3). Since Gen-

eral Digital has contro l of the firmware , customer s can

define the numbe r of temperatur e limits , their associated

temperatures , the brightnes s reductio n require d at each

level and the clearing temperatures . The defaul t fir mware provide s three over-temperatur e limits with brightness

reductio n values of 80%, 60% and off, respectivel y.

BRIGHTNESS CONTROL

A unique feature of the General Digital’s LED Backlight

Controller PCB is an interface to support a pair of bright-

ness sensors (I2C). Feedback from the optical sensor allows

the controller to maintain a constant backlight brightness

even when the ambient temperatures vary drasticall y.

This greatly improves functionality since the cur rent

draw and brightness of the LED is directly influenced by

its temperature.

CONVENTIONAL DESIGNS

Most commercial LED rails for LCD displays are designed

to be driven serially (Fig. 1). The prima ry advantage of

this design approach is that the associated controller

requires only a very low output current. Typicall y, the

controllers occupy a small footprint since the low output

override requires only small traces. Howeve r, the glaring

disadvantage of a serial driven LED rail, and associated

controlle r, is that there is no soft failure mechanism in the

event of an individual LED failure. A failure of a single

LED will render the entire rail inoperable. The other

disadvantage is that the LED controller will produce a

very high output voltage (100 Vdc typical), which

constitutes a haz- ardous voltage and complicates its

integration.

OUR DESIGN

General Digital’s™ LED backlight designs are designed to

provide a very low cost of ownership by ensuring extended

operational life of the LEDs. Our LED rails use a serial- parallel design philosoph y, whereby we drive groupings of

multiple LEDs. Howeve r, what differentiates our design

approach from other ’s is that each of the LED groupings

is driven in a parallel manner (Fig. 2). The prima ry benefi t

is that a single LED failure will only affect its immediate

grouping (soft failure), but will not affect any of the other

groupings of LEDs. The benefi t is that singular or multi-

ple LED failures will not render the monitor inoperable,

and in most cases will still provide a very unifo rm back

light. This non-catastrophic failure condition is essential

for mission critical applications. It should also be noted

that our LED Controller can support up to 10 amps o

output current. This is far greater than typical cur rent

regulated LED module drivers, which only support 1 amp

per module. Prior to the advent of our LED controlle r, ou

typical sunlight/NVIS backlight for 19" display required

six LED modules to drive our LED rails. Substituting ou

LED Controller saved considerable expense, mechanical

space and weight. Furthe rmore, our controller eliminated

the need for technician time to calibrate each of the indi

vidual modules, providing further cost savings.

PROGRAMMABILITY

The performance of the LED controller is programmableat the facto ry to meet the specific requirements of each

application. The following parameters are programmable:

„ Maximum / Minimum Brightness of Sunlight Readable

LED Rails

„ Maximum / Minimum Brightness of NVIS LED Rails

„ Current Limiting of Sunlight Readable & NVIS

LED Rails

» Monitor Maximum Output of Sunlight Readable

Rails to Prevent Thermal Runaway Under Extreme

Thermal Environments

» Ensures Long Life of LEDs

„ Define Brightness of Sunlight Readable and NVIS

Modes When Switching Modes

» Brightness Algorithm Choices

• Default Brightness (value defined by user)

• Last Brightness (recalls last setting)

• Based on Potentiometer Position

• Custom

„ Define “Over Temperature” Brightness Reduction

Parameters (can be disabled)

» Number of Over Temperature Limits

(set points)

» Corresponding Temperature Value for Each Limit

(set point)

» Target Backlight Brightness (e.g., 80%) for Each

Temperature Limit




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FEATURE BENEFIT

Support for Brightness Sensors (Up to Two)

- One (1) LED Rail – Sunlight R eadable (SR)and Night

Vision Imaging System (NVIS)

- One (1) Ambient Light with Proximity Sensor

Consistent and Predictable Luminance

Sensors provide real-time brightness feedback from the L ED backlights to

the microprocessor so that the brightness can automatically be corrected for

changes due to ambient temperature fluctuations, increased current draw of the L E Ds ,decay of the LED, etc. Ensures consistent performance from one

monitor to another despite inherent component tolerances.

Maximizes Backlight Life, Power and Energy Savings

Allowsfor automatic brightness/dimming control of L ED 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 Profi les

Custom control profiles (firmware)can be created by General Digital for the

L EDController to meet specific customer requirements.

Support for Multiple Temperature Sensors

- Embedded on LED Rail

- Other

Prevent Critical Hardware Failures

Provides real-time temperature feedback from the LE Drails. 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.

Monitor other critical temperature hot spots within the integrated solution/

monitor .

Current Limiting for LEDRails (SR and NVIS) Inherently, LEDswil l draw more current as they heat up. After a certain

temperature threshold is exceeded, the L E D s power efficiencyand brightness

willdegrade; furthermore, as the L E D slose brightness, they willcontinue todraw more current and dissipate more heat.

Prevention of Thermal R unaway

The LE Dcontroller monitors the current to each LE Drail 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 directlylimiting the power consumption of the backlight and indirectly

reducing the heat generated, the LE Dcontroller prevents over -temperatureconditions from developing. I f allowed to go unchecked, what could occur is

temporary or permanent failure of the liquid crystal material and/or the LCD’s

optical filmsand 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.



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FEATURE BENEFIT

Hardware Protection Critical Failure Detection

In the event that the microprocessor or either of the digital potentiometers

fails, the backlights will be intentionally shut off. Thiswi l l prevent the LEDs

from entering a “runaway” thermal condition that could lead to permanent

damage of the LCD and its infrastructure.

Programability

- Automatic Ove r -Temperature “Soft Failure” Algorithm

- Minimum/Maximum Sunlight R eadable Brightness

- Minimum/Maximum NVIS Brightness

- Current Limits

- Define Brightness of Sunlight R eadable and NVIS

Modes when Switching Between Modes

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 L E D

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 willshut 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

limitsand the percentage of brightness for each limit.


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.


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.

Maximizes Backlight Life/Critical Failure Protection

Prevents thermal runaway under extreme thermal environment variations and

increases L E D longevity.


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

Backlight Designs

Soft Failure Design

General Digital’s LED backlight rails utilizea 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.



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ORDERING/OPTIONS

P/N 21-101...Support for Sunlight Readable and NVIS

P/N 21-127...Support for Sunlight Readable Only

PHYSI CAL CHAR ACTERISTICS

Weight: 74.2 grams

Size: 4.000" x 3.000" x 0.625"

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

Mode Connector: J8

The rmistor Input: J10, J13

Brightness Sensor Input: J11, J12

Figure 3

Figure 4

Figure 5

PWBLayout

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Symbol Parameter Value Unit

Vin Supply Voltage 1.00 to 20.00 Vdc

Vsig Voltage to A ll Input Pins -0.7 to 5.25 Vdc

Imax Input Current 10 Adc

Pmax Output power 138 Watts

Top Operating Temperature -40 to +75 C°

Tst Storage Temperature -60 to +150 C°

Pin Signal

1 Video OK Input

2 Ground

3 Video Standby Input

4 Video OK Input

5 Ground

6 Video Standby Input

Symbol Parameter Typical Value Unit

Vin Supply Voltage 12.0 to 15.3 Vdc

Lhigh Logic Input High 1.27 to 5.00 Vdc

Llow Logic Input Low 0 to 0.70 Vdc

Din Dimming Potentiometer 0 to 5.00 Vdc

Pin Signal

1 Signal Input High=NVIS Mode

2 Ground

Pin Signal

1 +12 to 15Vdc

2 +12 to 15Vdc

3 +12 to 15Vdc

4 +12 to 15Vdc

5 Ground

6 Ground

7 Ground

8 Ground

Pin Signal

1 Thermistor In

2 Ground

Pin Signal

1 + Vout

2 NC

3 Ground

Pin Signal

1 3.3 Vdc

2 Ground

3 A0

4 A1

5 SCL

6 SDA

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MAXIMUM RATINGS* J5: Video Status I/O Pass Through

Mating Connector: JST XHP-6

*Maximum ratings denote the values beyond which damage will

occur .

RECOMMENDED OPERATING VALUES

J6 and J7: NVISLEDRail Output

Mating Connector: Tyco Electronics 640250-2

Pin Signal

1 + Vout

2 Ground

CONNEC TORS

J1: Voltage Input


J8: NVISControl Input


J9: Push Button Dimming Input


Pin Operation

1 Brightness Up Push Button

2 Brightness Down Push Button

3 Ground

J2 and J3: Sunlight L E D Rail Output


J10, J13: Thermistor Input

Mating Connector: Molex 51021-0200

Thermistor: U.S. Sensor PS10352

J4: Analog Dimming Input


J11, J12: Brightness Sensor Input

Use General Digital 21-147

Pin Signal

1 + 5Vdc Output for Potentiometer

2 Dimming Control Voltage Input

3 Ground

4 Ground

G e n e r al D i g i t a l™ C o r p o r a t i on 8 N u t m eg R o ad S o u th S o u th W i n d s o r , CT 0 6 0 74 To l l - F r ee P h o n e:

8 0 0 . 9 5 2 . 2 5 3 5

L o c a l: (8 60) 28 2- 29 00 F a x: (8 60) 28 2- 22 44 E - m a i l: g d _ d s @ G e n e r a l D i g i t a l . c om W eb S i t e:

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Led Backlight Controller Ds NoPW

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