SLVS822F March   2009  – April 2024 TPS798-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 Dissipation Ratings
    7. 5.7 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagrams
    3. 6.3 Feature Description
      1. 6.3.1 Adjustable Operation
      2. 6.3.2 Output Capacitance and Transient Response
      3. 6.3.3 Calculating Junction Temperature
      4. 6.3.4 Protection Features
    4. 6.4 Device Functional Modes
      1. 6.4.1 Low-Voltage Tracking
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
      1. 7.3.1 Thermal Considerations
      2. 7.3.2 Thermal Layout Considerations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Receiving Notification of Documentation Updates
    2. 8.2 Support Resources
    3. 8.3 Trademarks
    4. 8.4 Electrostatic Discharge Caution
    5. 8.5 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

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

7.3.2 Thermal Layout Considerations

The amount of heat that an LDO linear regulator generates is directly proportional to the amount of power the device dissipates during operation. All integrated circuits have a maximum allowable junction temperature (TJ max) above which normal operation is not assured. The operating environment must be designed so that the operating junction temperature (TJ) does not exceed the maximum junction temperature (TJ max). The two primary environmental variables that can be used to improve thermal performance are air flow and external heat sinks. The purpose of this section is to help determine the proper operating environment for a linear regulator that operates at a specific power level.

In general, the maximum expected power (PD max) consumed by a linear regulator is computed as shown in Equation 6:

Equation 6. PDmax = (VIN(avg) – VOUT(avg)) × IOUT(avg) + VI(avg) × IQ

where:

  • VIN(avg) is the average input voltage
  • VOUT(avg) is the average output voltage
  • IOUT(avg) is the average output current
  • IQ is the quiescent current

For most TI LDO regulators, the quiescent current is insignificant compared to the average output current; therefore, the term VIN(avg) × IQ can be ignored. The operating junction temperature is computed by adding the ambient temperature (TA) and the increase in temperature as a result of the regulator power dissipation. The temperature rise is computed by multiplying the maximum expected power dissipation by the sum of the thermal resistances between the junction and the case (RθJC), the case to heat sink (RθCS), and the heat sink to ambient (RθSA). Thermal resistances are measurements of how effectively an object dissipates heat. Typically, the larger the device, the more surface area available for power dissipation and the lower the device thermal resistance. Figure 7-4 shows the relationship between power dissipation and temperature.

GUID-70B692EB-70B2-4DB4-B4AE-E93AFBECAC6C-low.gifFigure 7-4 Power Dissipation vs Temperature