SCPS292 July   2025 TCA9539A-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 I2C Interface Timing Requirements
    7. 5.7 RESET Timing Requirements
    8. 5.8 Switching Characteristics
    9. 5.9 Typical Characteristics
  7. 6 Parameter Measurement Information
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 I/O Port
      2. 7.3.2 RESET Input
      3. 7.3.3 Interrupt ( INT) Output
    4. 7.4 Device Functional Modes
      1. 7.4.1 Power-On Reset
    5. 7.5 Programming
      1. 7.5.1 I2C Interface
    6. 7.6 Register Map
      1. 7.6.1 Device Address
      2. 7.6.2 Control Register And Command Byte
  9. 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 Calculating Junction Temperature and Power Dissipation
        2. 8.2.2.2 Minimizing ICC When I/Os Control LEDs
      3. 8.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Documentation Support
      1. 9.1.1 Related Documentation
    2. 9.2 Receiving Notification of Documentation Updates
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

8.2.2.1 Calculating Junction Temperature and Power Dissipation

When designing with the TCA9539A-Q1, it is important that the Recommended Operating Conditions not be violated. Many of the parameters of this device are rated based on junction temperature, so junction temperature must be calculated in order to verify that safe operation of the device is met. The basic equation for junction temperature is shown in Equation 3.

Equation 3. TCA9539A-Q1

θJA is the standard junction to ambient thermal resistance measurement of the package, as seen in Section 5.4 table. Pd is the total power dissipation of the device, and the approximation is shown in Equation 4.

Equation 4. TCA9539A-Q1

Equation 4 is the approximation of power dissipation in the device. The equation is the static power plus the summation of power dissipated by each port (with a different equation based on if the port is outputting high, or outputting low. If the port is set as an input, then power dissipation is the input leakage of the pin multiplied by the voltage on the pin). Note that this ignores power dissipation in the INT and SDA pins, assuming these transients to be small. They can be included in the power dissipation calculation by using Equation 5 to calculate the power dissipation in INT or SDA while pulling low. This provides the maximum power dissipation.

Equation 5. TCA9539A-Q1

Equation 5 shows the power dissipation for a single port which is set to output low. The power dissipated by the port is the VOL of the port multiplied by the current it is sinking.

Equation 6. TCA9539A-Q1

Equation 6 shows the power dissipation for a single port which is set to output high. The power dissipated by the port is the current sourced by the port multiplied by the voltage drop across the device (difference between VCC and the output voltage).