The underlying thermal limitation for the DLPC34xx controller is that the maximum operating junction temperature (TJ) not be exceeded (this is defined in Recommended Operating Conditions).
Some factors that influence TJ are as follows:
The controller package is designed to primarily extract heat through the power and ground planes of the PCB. Thus, copper content and airflow over the PCB are important factors.
The recommends maximum operating ambient temperature (TA) is provided primarily as a design target and is based on maximum DLPC34xx controller power dissipation and RθJA at 0 m/s of forced airflow, where RθJA is the thermal resistance of the package as measured using a glater test PCB with two, 1-oz power planes. This JEDEC test PCB is not necessarily representative of the DLPC34xx controller PCB, so the reported thermal resistance may not be accurate in the actual product application. Although the actual thermal resistance may be different, it is the best information available during the design phase to estimate thermal performance. TI highly recommended that thermal performance be measured and validated after the PCB is designed and the application is built.
To evaluate the thermal performance, measure the top center case temperature under the worse case product scenario (maximum power dissipation, maximum voltage, maximum ambient temperature), and validate the controller does not exceed the maximum recommended case temperature (TC). This specification is based on the measured φJT for the DLPC34xx controller package and provides a relatively accurate correlation to junction temperature.
Take care when measuring this case temperature to prevent accidental cooling of the package surface. TI recommends a small (approximately 40 gauge) thermocouple. Place the bead and thermocouple wire so that they contact the top of the package. Cover the bead and thermocouple wire with a minimal amount of thermally conductive epoxy. Route the wires closely along the package and the board surface to avoid cooling the bead through the wires.