TIDUEA0A March   2019  – September 2020

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
    1. 1.1 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
    3. 2.3 Highlighted Products
      1. 2.3.1 Device Recommendation
      2. 2.3.2 Digital Temperature Sensor - TMP117
      3. 2.3.3 Digital Temperature Sensor - TMP116
      4. 2.3.4 ESD Protection Devices
    4. 2.4 System Design Theory
      1. 2.4.1 PT100, PT500, PT1000 based Measurement in Heat Meters
      2. 2.4.2 TMP117 Configuration as Temperature Sensor
      3. 2.4.3 Digital RTD Solution Using TMP117
      4. 2.4.4 Ambient Temperature Considerations
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Required Hardware and Software
      1. 3.1.1 Hardware
      2. 3.1.2 Interface Test Software for TMP116
    2. 3.2 Testing and Results
      1. 3.2.1 Test Setup for Performance Testing
      2. 3.2.2 EMI and EMC Test Requirements for DRTD
      3. 3.2.3 TMP117 EMI/EMC Test Results
      4. 3.2.4 TMP117 Based Temperature Probe Measurement Performance Test Results
      5. 3.2.5 TMP116 Based Temperature Probe Measurement Performance Test Results
      6. 3.2.6 I2C-bus Cable Length Considerations
      7. 3.2.7 Power Supply
      8. 3.2.8 ESD Test Results for TMP116
      9. 3.2.9 Summary
  9. 4Design Files
    1. 4.1 Schematics
    2. 4.2 Bill of Materials
    3. 4.3 Layout Prints
    4. 4.4 Altium Project
    5. 4.5 Gerber Files
    6. 4.6 Assembly Drawings
  10. 5Software Files
  11. 6Related Documentation
    1. 6.1 Trademarks
  12. 7About the Author
  13. 8Revision History

3.2.6 I2C-bus Cable Length Considerations

The 4-wire digital interface with I2C-bus operation has been verified with multiple DRTD probes of 2, 4, 6, 8 and 10-m cable length. An external 4.7-kΩ pullup resistors for the SCL line has been used.

Note that the I2C-bus specification defines maximum bus capacity which limits the possible cable length. The distance achieved (10 m was the maximum cable length DRTD probe available) depends on the parameters of the 4-wire cable used as well as from the driving capability of the I2C-master device (here a MSP430FR6047 MCU). Multiple oscilloscope plots of data transfer taken for cable lengths of 6 m, 8 m, and 10 m show that for longer cable distances bit errors probability increases as the signal rise and fall times get longer and the total capacitance of each wire goes beyond the I2C-bus limit of 400-pF maximum due to its cable length.

Nevertheless, the I2C specification mentions that using higher driver strength device than 3 mA for Fast mode with 400 kHz clock frequency can help overcome this limitation. The MSP430FR6047 Digital IO pins can drive up about 10-mA low-level output current at about 0.6-V output voltage, when the MSP430 supply voltage VCC = 2.2 V.

It is user's responsibility to verify which is the maximum achievable cable length for worst case conditions of both VDD supply voltage levels (for example, a primary battery LiMnO2, discharged down to 2.5 V) and the ambient operating temperature of the application (for example, Heat Meter).

The peak case ± 11.13 mK inaccuracy of the TIDA-010002 DRTD probe is significantly better than the limit of ±700 mK, set in prEN1434- 5:2014, when comparing each RTD sensor behavior with the ideal RTD plot using the EN 60751 Callender-Van-Dusen (CVD) reference equation. The compliance with this limit has to occur for 3 typical temperature points, for example at 10°C, 30°C, and 50°C, which is verified in Figure 3-8.