ZHCSKB0 October   2019 TMP63

ADVANCE INFORMATION for pre-production products; subject to change without notice.  

  1. 特性
  2. 应用
  3. 说明
    1.     Device Images
      1.      典型实施电路
      2.      典型电阻与环境温度间的关系
  4. 修订历史记录
  5. Pin Configuration and Functions
    1.     Pin Functions
  6. Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
    4. 7.4 Device Functional Modes
  8. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Thermistor Biasing Circuits
        1. Design Requirements
        2. Detailed Design Procedure
          1. Thermal Protection With Comparator
          2. Thermal Foldback
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11器件和文档支持
    1. 11.1 接收文档更新通知
    2. 11.2 支持资源
    3. 11.3 商标
    4. 11.4 静电放电警告
    5. 11.5 Glossary
  12. 12机械、封装和可订购信息


机械数据 (封装 | 引脚)
散热焊盘机械数据 (封装 | 引脚)

Thermal Foldback

One application that uses the output voltage of the TMP63 in an active control circuit is thermal foldback. This is performed to reduce, or fold back, the current driving a string of LEDs, for example. At high temperatures, the LEDs begin to heat up due to environmental conditions and self heating. Thus, at a certain temperature threshold based on the LED's safe operating area, the driving current must be reduced to cool down the LEDs and prevent thermal runaway. The TMP63 voltage output increases with temperature when the output is in the lower position of the voltage divider and can provide a response used to fold back the current. Typically, the current is held at a specified level until a high temperature is reached, known as the knee point, where the current must be rapidly reduced. To better control the temperature/voltage sensitivity of the TMP63, a rail-to-rail operational amplifier is used. In the example shown in Figure 8, the temperature “knee” where the foldback begins is set by the reference voltage (2.5 V) at the positive input, and the feedback resistors set the response of the foldback curve. The foldback knee point may be chosen based on the output of the voltage divider and the corresponding temperature from Equation 5 (like 110°C, for example). A buffer is used in-between the voltage divider with RTMP63 and the input to the op amp to prevent loading and variations in VTEMP.

TMP63 TMP63_Therm_Foldback.gifFigure 8. Thermal Foldback Using TMP63 Voltage Divider and a Rail-to-Rail Op Amp

The op amp will remain high as long as the voltage output is below VRef. When the temperature goes above 110°C, then the output will swing low to the 0-V rail of the op amp. The rate at which the foldback occurs is dependent on the feedback network, RFB and R1, which varies the gain of the op amp, G, given by Equation 6. This in return controls the voltage/temperature sensitivity of the circuit. This voltage output is fed into a LED driver IC that will adjust output current accordingly. The final output voltage used for thermal foldback is VOUT, and is given in Equation 7. In this example where the knee point is set at 110°C, the output voltage curve is as shown in Figure 9.

Equation 5. TMP63 Therm_FB_EQ1.gif
Equation 6. TMP63 Therm_FB_EQ2.gif
Equation 7. TMP63 Therm_FB_EQ3.gif
TMP63 D014_SBOS921.gifFigure 9. Thermal Foldback Voltage Output Curve