SLOS877C October   2014  – April 2021 TMP451-Q1

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 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Timing Characteristics for Figure 1-1
    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 Temperature Measurement Data
        1. 7.3.1.1 Standard Binary to Decimal Temperature Data Calculation Example
        2. 7.3.1.2 Standard Decimal to Binary Temperature Data Calculation Example
      2. 7.3.2 Series Resistance Cancellation
      3. 7.3.3 Differential Input Capacitance
      4. 7.3.4 Filtering
      5. 7.3.5 Sensor Fault
      6. 7.3.6 ALERT and THERM Functions
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode (SD)
    5. 7.5 Programming
      1. 7.5.1 Serial Interface
        1. 7.5.1.1 Bus Overview
        2. 7.5.1.2 Bus Definitions
        3. 7.5.1.3 Serial Bus Address
        4. 7.5.1.4 Read and Write Operations
        5. 7.5.1.5 Timeout Function
        6. 7.5.1.6 High-Speed Mode
    6. 7.6 Register Map
      1. 7.6.1 Register Information
        1. 7.6.1.1  Pointer Register
        2. 7.6.1.2  Temperature Registers
        3. 7.6.1.3  Status Register
        4. 7.6.1.4  Configuration Register
        5. 7.6.1.5  Conversion Rate Register
        6. 7.6.1.6  One-Shot Start Register
        7. 7.6.1.7  η-Factor Correction Register
        8. 7.6.1.8  Offset Register
        9. 7.6.1.9  General Call Reset
        10. 7.6.1.10 Identification 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
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Receiving Notification of Documentation Updates
    2. 11.2 Support Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

8.2.1 Design Requirements

The TMP451-Q1 device is designed to be used with either discrete transistors or substrate transistors built into processor chips and ASICs. Either NPN or PNP transistors can be used, as long as the base-emitter junction is used as the remote temperature sense. NPN transistors must be diode-connected. PNP transistors can either be transistor- or diode-connected (see Figure 8-1).

Errors in remote temperature sensor readings are typically the consequence of the ideality factor and current excitation used by the TMP451-Q1 device versus the manufacturer-specified operating current for a given transistor. Some manufacturers specify a high-level and low-level current for the temperature-sensing substrate transistors. The TMP451-Q1 device uses 7.5 μA for ILOW and 120 μA for IHIGH.

The ideality factor (η) is a measured characteristic of a remote temperature sensor diode as compared to an ideal diode. The TMP451-Q1 allows for different η-factor values; see the η-Factor Correction Register section.

The ideality factor for the TMP451-Q1 device is trimmed to be 1.008. For transistors that have an ideality factor that does not match the TMP451-Q1, Equation 4 can be used to calculate the temperature error.

Note:

For the equation to be used correctly, actual temperature (°C) must be converted to Kelvin (K).

Equation 4. GUID-F0663989-B58B-4358-9967-650B5B519049-low.gif

where

  • TERR = error in the TMP451-Q1 device because η ≠ 1.008
  • η = ideality factor of remote temperature sensor
  • T(°C) = actual temperature
  • Degree delta is the same for °C and K.

For η = 1.004 and T(°C) = 100°C:

Equation 5. GUID-83D841AE-1F09-47AA-A056-869712E502C9-low.gif

If a discrete transistor is used as the remote temperature sensor with the TMP451-Q1, the best accuracy can be achieved by selecting the transistor according to the following criteria:

  1. Base-emitter voltage > 0.25 V at 7.5 μA, at the highest sensed temperature.
  2. Base-emitter voltage < 0.95 V at 120 μA, at the lowest sensed temperature.
  3. Base resistance < 100 Ω.
  4. Tight control of VBE characteristics indicated by small variations in hFE (that is, 50 to 150).

Based on this criteria, two recommended small-signal transistors are the 2N3904 (NPN) or 2N3906 (PNP).