SLVS490K December   2003  – June 2024

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Description (continued)
  6. 5 Pin Configuration and Functions
  7. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 Recommended Operating Conditions
    3. 6.3 Thermal Information
    4. 6.4 Electrical Characteristics
    5. 6.5 Typical Characteristics (TPS2061, TPS2062, TPS2065, and TPS2066)
    6. 6.6 Typical Characteristics (TPS2063 & TPS2067)
  8. 7 Parameter Measurement Information
  9. 8 Detailed Description
    1. 8.1  Functional Block Diagram
    2. 8.2  Power Switch
    3. 8.3  Charge Pump
    4. 8.4  Driver
    5. 8.5  Enable ( ENx or ENx)
    6. 8.6  Current Sense
    7. 8.7  Overcurrent
      1. 8.7.1 Overcurrent Conditions (TPS2063 and TPS2067)
      2. 8.7.2 Overcurrent Conditions (TPS2061, TPS2062, TPS2065, and TPS2066)
    8. 8.8  Overcurrent ( OCx)
    9. 8.9  Thermal Sense
    10. 8.10 Undervoltage Lockout
  10. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1  Power-supply Considerations
      2. 9.1.2  OC Response
      3. 9.1.3  Power Dissipation and Junction Temperature
      4. 9.1.4  Thermal Protection
      5. 9.1.5  Undervoltage Lockout (UVLO)
      6. 9.1.6  Universal Serial Bus (USB) Applications
      7. 9.1.7  Host/Self-Powered and Bus-powered Hubs
      8. 9.1.8  Low-power Bus-powered and High-Power Bus-Powered Functions
      9. 9.1.9  USB Power-distribution Requirements
      10. 9.1.10 Generic Hot-Plug Applications
  11. 10Device and Documentation Support
    1. 10.1 Device Support
    2. 10.2 Documentation Support
    3. 10.3 Receiving Notification of Documentation Updates
    4. 10.4 Support Resources
    5. 10.5 Trademarks
    6. 10.6 Electrostatic Discharge Caution
    7. 10.7 Glossary
  12. 11Revision History
  13. 12Mechanical, Packaging, and Orderable Information

9.1.3 Power Dissipation and Junction Temperature

The low on-resistance on the N-channel MOSFET allows the small surface-mount packages to pass large currents. The thermal resistances of these packages are high compared to those of power packages; it is good design practice to check power dissipation and junction temperature. Begin by determining the rDS(on) of the N-channel MOSFET relative to the input voltage and operating temperature. As an initial estimate, use the highest operating ambient temperature of interest and read rDS(on) from Figure 6-25. Using this value, the power dissipation per switch can be calculated by:

  • PD = rDS(on)× I2

Multiply this number by the number of switches being used. This step renders the total power dissipation from the N-channel MOSFETs.

The thermal resistance, RθJA = 1 / (DERATING FACTOR), where DERATING FACTOR is obtained from the Dissipation Ratings Table. Thermal resistance is a strong function of the printed circuit board construction , and the copper trace area connecting the integrated circuit.

Finally, calculate the junction temperature:

  • TJ = PD x RθJA + TA

Where:

  • TA= Ambient temperature °C
  • RθJA = Thermal resistance
  • PD = Total power dissipation based on number of switches being used.

Compare the calculated junction temperature with the initial estimate. If they do not agree within a few degrees, repeat the calculation, using the calculated value as the new estimate. Two or three iterations are generally sufficient to get a reasonable answer.