SLVSE84D December 2017 – July 2021 TLV767
The JEDEC standard now recommends the use of psi (Ψ) thermal metrics to estimate the junction temperatures of the linear regulator when in-circuit on a typical PCB board application. These metrics are not thermal resistance parameters and instead offer a practical and relative way to estimate junction temperature. These psi metrics are determined to be significantly independent of the copper area available for heat-spreading. The Thermal Information table lists the primary thermal metrics, which are the junction-to-top characterization parameter (ψJT) and junction-to-board characterization parameter (ψJB). These parameters provide two methods for calculating the junction temperature (TJ), as described in the following equations. Use the junction-to-top characterization parameter (ψJT) with the temperature at the center-top of device package (TT) to calculate the junction temperature. Use the junction-to-board characterization parameter (ψJB) with the PCB surface temperature 1 mm from the device package (TB) to calculate the junction temperature.
For detailed information on the thermal metrics and how to use them, see the Semiconductor and IC Package Thermal Metrics application report.