SBOS371B August   2006  – October 2014 TMP401

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 Handling Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics: V+ = 3 V to 5.5 V
    6. 6.6 Timing Requirements
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Standard and Extended Temperature Measurement Range
      2. 7.3.2 Remote Sensing
    4. 7.4 Device Functional Modes
      1. 7.4.1 SMBus Alert Function
      2. 7.4.2 THERM (Pin 4) and ALERT/THERM2 (Pin 6)
      3. 7.4.3 Sensor Fault
      4. 7.4.4 High-Speed Mode
      5. 7.4.5 Shutdown Mode (SD)
      6. 7.4.6 One-Shot Conversion
      7. 7.4.7 General-Call Reset
    5. 7.5 Programming
      1. 7.5.1 Bus Overview
      2. 7.5.2 Serial Interface
      3. 7.5.3 Serial Bus Address
      4. 7.5.4 Read and Write Operations
      5. 7.5.5 Timeout Function
      6. 7.5.6 Timing Diagrams
    6. 7.6 Register Maps
      1. 7.6.1  Pointer Register
      2. 7.6.2  Temperature Registers
      3. 7.6.3  Limit Registers
      4. 7.6.4  Status Register
      5. 7.6.5  Configuration Register
      6. 7.6.6  Resolution Register
      7. 7.6.7  Conversion Rate Register
      8. 7.6.8  Identification Registers
      9. 7.6.9  Consecutive Alert Register
      10. 7.6.10 THERM Hysteresis Register
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Filtering
      3. 8.2.3 Application Curves
        1. 8.2.3.1 Series Resistance Cancellation
        2. 8.2.3.2 Differential Input Capacitance
  9. 9 Power-Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Measurement Accuracy and Thermal Considerations
      2. 10.1.2 Layout Considerations
    2. 10.2 Layout Examples
  11. 11Device and Documentation Support
    1. 11.1 Trademarks
    2. 11.2 Electrostatic Discharge Caution
    3. 11.3 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

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8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

8.1 Application Information

The TMP401 is a remote temperature sensor monitor that includes a built-in local temperature sensor. The remote temperature sensor diode-connected transistors are typically low-cost, NPN- or PNP-type transistors or diodes that are an integral part of microcontrollers, microprocessors, or FPGAs.

Remote accuracy is ±1°C for multiple device manufacturers, with no calibration required. The two-wire serial interface accepts SMBus write, read, send, and receive byte commands to program alarm thresholds and to read temperature data.

Features included in the TMP401 are series resistance cancellation, wide remote temperature measurement range (–40°C to +150°C), diode fault detection, and temperature alert functions.

8.2 Typical Application

ai_basic_connex_sbos371.gif
1. The diode-connected configuration provides better settling time. The transistor-connected configuration provides better series resistance cancellation. A 2N3906 PNP is used in this configuration.
2. In most applications, RS is < 1.5 kΩ.
3. In most applications, CDIFF is < 1000 pF.
Figure 24. Remote Noise Filtering

8.2.1 Design Requirements

The TMP401 device requires pull-up resistors on the SCL, SDA, ALERT/THERM2, and THERM pins. The recommended value for the pull-up resistors is 10-kΩ. A 0.1-μF bypass capacitor on the supply is recommended, as shown in Figure 24. The SCL and SDA lines can be pulled up to a supply that is equal to or higher than V+ through the pull-up resistors, but not to exceed (V+) + 0.5 V.

8.2.2 Detailed Design Procedure

Place the TMP401 device in close proximity to the heat source to be monitored, with proper layout for good thermal coupling. This placement ensures that temperature changes are captured within the shortest possible time interval. To maintain accuracy in applications that require air or surface temperature measurement, care must be taken to isolate the package and leads from ambient air temperature. A thermally-conductive adhesive is helpful in achieving accurate surface temperature measurement.

8.2.2.1 Filtering

Remote junction temperature sensors are usually implemented in a noisy environment. Noise is most often created by fast digital signals, and can corrupt measurements. The TMP401 has a built-in, 65-kHz filter on the inputs of D+ and D– to minimize the effects of noise. However, a bypass capacitor placed differentially across the inputs of the remote temperature sensor is recommended to make the application more robust against unwanted coupled signals. The value of the capacitor must be between 100 pF and 1 nF. Some applications attain better overall accuracy with additional series resistance. When series resistance is added, the value must not be greater than RS = 3 kΩ. If filtering is needed, the suggested component values are 100 pF and 50 Ω on each input. Exact values are application-specific.

8.2.3 Application Curves

8.2.3.1 Series Resistance Cancellation

Series resistance in an application circuit that typically results from printed circuit board (PCB) trace resistance and remote line length (see Figure 11) is automatically cancelled by the TMP401, preventing what otherwise results in a temperature offset. When using a 5-V supply voltage, a total of up to RS = 3 kΩ of series line resistance is cancelled by the TMP401, eliminating the need for additional characterization and temperature offset correction. Limit series line resistance to 500 Ω total when using a 3.3-V supply voltage. See Figure 25 and Figure 26 for details on the effect of series resistance and power-supply voltage on sensed remote temperature error.

tc_remote_err-series_res1_sbos371.gif
Figure 25. Remote Temperature Error vs Series Resistance (Diode-Connected Configuration; see Figure 24)
tc_remote_err-series_res2_sbos371.gif
Figure 26. Remote Temperature Error vs Series Resistance (Transistor-Connected Configuration; see Figure 24)

8.2.3.2 Differential Input Capacitance

The TMP401 tolerates differential input capacitance of up to 1000 pF with minimal change in temperature error. The effect of capacitance on sensed remote temperature error is illustrated in Figure 27.

tc_remote_err-diff_cap_sbos371.gif
Figure 27. Remote Temperature Error vs Differential Capacitance
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