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									NXP LED LCD TV
Use of Temperature Sensor

April 2010
                                                                                                        Temp Sensor is Panel
       LCD TV                                                           Memory
                                                                                         DDR             needed here!
                                                                                      terminator
                                                                                                               LED Back
                                                                                                                lighting




                                                ADC
                                  ESD
                                                                                                               Controller
                                                          MOSFETs                      Logic
                                  ESD
AV Inputs




                                                                                                         ESD
                                                                                                                    LVDS
                                                                                        GA

                                                µC
                                        CEC




                                                                                                                        ESD
            USB




                                                                Signal Processing
                                                                      Board
            HDMI




                                              Receiver




                                                                                                                  Audio
                                               HDMI
                                  ESD




                                                         Processor 1       UARTs     Processor 2                  Amp

                                                                                                                  Head
                   Tuner                                           DC-DC                                          phone
                   /SAW                                                                                            Amp


                                           I2C Bus                       I2C bus
                           IR




                                          Expander
               board




                                                                            Standby Power                       Temp
                           GPIO
                Key




                                                         Power Supply                              µC
                                                                                Supply                         Sensor
                                          Interface
                                          functions
                                                            mains

                                                                                                                              2
Why Temp Sensor is needed for LED Backlight
LCD TV?
 In LED backlight LCD TV, LEDs require precise power and thermal
 management systems, since most of the electrical energy supplied to an LED
 is converted to heat rather than light.
 Without adequate thermal management, this heat will have a negative effect on
 both the LED’s lifespan and color output.
 The life of an LED is defined as the time for light to reach 50% original value.
 The average life is 100K hours. A thermal runaway condition can shorten
 LEDs life and eventually break down the LEDs in the TV sets. When the LEDs
 break down the repair will be rather complex.
 The Temperature increase also causes the LED dominant wavelength
 increase, that means the dimming values for each LED need to be recalculated
 to ensure that the targeted color points is still being met at the elevated
 temperature.
 So, LED backlighting needs to be protected by temp sensor, like NXP LM75B.


                                                                                    3
LM75B - Digital Temp Sensor & Thermal Watchdog
Features/Benefits
  Pin for pin replacement for industry standard LM75 and LM75A
  Temperature range from -55 °C to +125 °C
  Temperature accuracy of ±2 °C from -25 °C to +100 °C and ±3 °C from -55 °C to +125 °C
  Programmable temperature threshold & hysteresis set points
  11 bit ADC that offers a temp resolution of 0.125 °C
  Supply current of 1uA in shutdown mode for power conservation
  Stand-alone operation as thermostat at power-up
  Low cost/high volume manufacturing
  Small 8-pin pkg types: SO8, TSSOP8, XSON8U (3 mm x 2 mm)

LM75B Application in LED backlight LCD TV
  Success story in global TV manufacturers.
  LM75B is used to sense the temperature of LED (e.g., when the LED is overheating,
  decrease brightness of LED and increase the contrast of LED to keep the screen clear).



                                                                                           4
LM75B improvements over LM75A




                                5
LM75B Competition Information
- Digital Temp Sensor (LM75B) VS Thermistor
Digital Temp Sensor
  Integrated circuit with built-in circuitry to           VCC                          DIGITAL

  measure and store temperature data                  =       ANALOG VOUT   +    ADC
                                                                                          I/F
                                                                                         I2C
                                                          GND   TS                     SMBUS
                                                                                         SPI
  No need to calibrate
                                                                            or
  Thermal watchdog
                                                                       V+              DIGITAL
  Sense between -55°C to 125°C (good                            ANALOG
                                                                  TS   V-
                                                                            +    ADC
                                                                                          I/F
                                                                                         I2C
                                                                                       SMBUS
  virtually for all equipments/systems)                                                  SPI




Thermistor
 Need to calibrate
 Normal Temp level thermistor can sense up to 150°C
 Low cost




                                                                                                 6
LM75B Competition Information
- LM75B VS Other Competitor’s Digital Temp Sensor
LM75B Selling Points
  Pin to pin replacement for industry standard LM75 and LM75A
  Higher ESD protection performance: HBM 4500V, MM 450V, CDM 2000V
  NXP LM75B has an extra XSON8U package
  Better price and delivery support than other competitors


Other Pin to Pin Competitive Devices
  TI TMP75 – NXP LM75B is more range for cold temp and simple to use (don’t need
  configure resolution bit).
  ADI ADT75 – Similar with NXP LM75B but with 12bit ADC.
  NS LM75B – NXP has better resolution (11 vs 9 bit) and lower power consumption.
  ST STLM75 – NXP has better resolution (11 vs 9 bit) and shorter conversion time (100 VS
  150 ms).



                                                                                        7

								
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