The underlying thermal limitation for the DLPC34xx controller is that the maximum operating junction temperature (T_J) not be exceeded (this is defined in the Recommended Operating Conditions section).

Some factors that influence T_J are as follows:

• operating ambient temperature
• airflow
• PCB design (including the component layout density and the amount of copper used)
• power dissipation of the DLPC34xx controller
• power dissipation of surrounding components

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 (T_A) is provided primarily as a design target and is based on maximum DLPC34xx controller power dissipation and R_θJA at 0 m/s of forced airflow, where R_θJA is the thermal resistance of the package as measured using a JEDEC defined standard 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 (T_C). This specification is based on the measured φ_JT 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.