SBOSA41A May   2023  – September 2023 TMP4718

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Revision History
  6. 5 Device Comparison
  7. 6 Pin Configuration and Functions
  8. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 I2C Interface Timing
    7. 7.7 Timing Diagrams
    8. 7.8 Typical Characteristics
  9. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 1.2-V Logic Compatible Inputs
      2. 8.3.2 Series Resistance Cancellation
      3. 8.3.3 Device Initialization, Resistor Decoding, and Default Temperature Conversion
      4. 8.3.4 Adjustable Default T_CRIT High-Temperature Limit
      5. 8.3.5 ALERT and T_CRIT Output
      6. 8.3.6 Fault Queue
      7. 8.3.7 Filtering
      8. 8.3.8 One-Shot Conversions
    4. 8.4 Device Functional Modes
      1. 8.4.1 Interrupt and Comparator Mode
        1. 8.4.1.1 Interrupt Mode
        2. 8.4.1.2 Comparator Mode
        3. 8.4.1.3 T_CRIT Output
      2. 8.4.2 Shutdown Mode
      3. 8.4.3 Continuous Conversion Mode
    5. 8.5 Programming
      1. 8.5.1 Temperature Data Format
      2. 8.5.2 I2C and SMBus Interface
      3. 8.5.3 Device Address
      4. 8.5.4 Bus Transactions
        1. 8.5.4.1 Writes
        2. 8.5.4.2 Reads
      5. 8.5.5 SMBus Alert Mode
    6. 8.6 Register Map
  10. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curves
    3. 9.3 Power Supply Recommendations
    4. 9.4 Layout
      1. 9.4.1 Layout Guidelines
      2. 9.4.2 Layout Example
  11. 10Device and Documentation Support
    1. 10.1 Documentation Support
      1. 10.1.1 Related Documentation
    2. 10.2 Receiving Notification of Documentation Updates
    3. 10.3 Support Resources
    4. 10.4 Trademarks
    5. 10.5 Electrostatic Discharge Caution
    6. 10.6 Glossary
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

9.2.2 Detailed Design Procedure

The ideality factor (η) is a measured characteristic of a remote temperature sensor diode as compared to an ideal diode. Compensating for ideality factor differences is simple if the diode manufacturer specifies the n-factor in the respective data sheet. If the ideality factor of the transistor is not specified, the manufacturer may be able to provide the n-factor value by a special request.

The TMP4718 provides an offset register to allow for a one point offset calibration that compensates for errors. Temperature errors associated with ideality factors of different processors or transistor types may be reduced in a specific temperature range of concern through use of offset calibration. Typical ideality factor specification differences cause a gain variation of the transfer function, so the center of the temperature range can be used as the target temperature for calibration purposes. The TMP4718 is calibrated for the ideality factor of 1.004, so use Equation 1 to calculate the required temperature correction factor (TCF) needed to compensate for a target ideality factor that differs from 1.004.

Equation 1. T C F = η S E N S O R   –   η D I O D E η S E N S O R × ( T C R + 273 K )

where:

  • ηSENSOR is the ideality factor of the temperature sensor, In the case of TMP4718, ηSENSOR is calibrated to approximately 1.004.

  • ηDIODE is the ideality factor of the thermal diode integrated in a processor or a discrete transistor used to measure the temperature at a remote spot.
  • TCR is the temperature value at the center of the temperature range of interest.
  • TCF is the temperature to compensate for a target ideality factor that can be programmed to the offset register for more accuracy temperature measurement.

In this example, the temperature of interest is from 60°C to 100°C, therefore the 80°C is the center of the temperature range and shall be used in the equation for calculation. The MMBT3906FZ-7B bipolar transistor, which has an ideality factor of approximately 1.01, is selected for this design example. Use Equation 2 to calculate the correction factor:

Equation 2. T C F = 1.004   –   1.01 1.004 × 80 + 273 K = – 2.11

The TMP4718 has a remote temperature resolution of 0.125°C. Therefore, 2.125°C is the closest value that can be programmed into the offset register to be subtracted from the remote temperature sensor temperature readings to compensate for the differing typical ideality factors.

The design calls for the default T_CRIT high-temperature limit of 99°C at device power up, which is programmed using the pullup resistors on ALERT and T_CRIT pins. Referring to Adjustable Default T_CRIT High-Temperature Limit, the 99°C trip point requires a 7.5-kΩ pullup resistor on the ALERT pin and a 10.5-kΩ pullup resistor on the T_CRIT pin. The default limit allows the T_CRIT pin to engage at the desired threshold and alerts the system of a thermal condition at device power up without any initial software configuration.

Remote junction temperature sensors are usually implemented in a noisy environment. Noise is most often created by fast digital signals, and noise can corrupt measurements. The TMP4718 device 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. For this capacitor, select a value of between 100 pF and 3 nF. Some applications attain better overall accuracy with additional series resistance; however, this increased accuracy is application-specific. When series resistance is added, the total value should not be greater than 1 kΩ. If filtering is required, suggested component values are 470 pF and 50 Ω on each input; exact values are application-specific.