DLPS117B July 2018 – October 2020 DLPC6421
The underlying thermal limitation for the DLPC6421 device is that the maximum operating junction temperature (TJ) not be exceeded (this is defined in the Section 6.3). This temperature is dependent on operating ambient temperature, airflow, PCB design (including the component layout density and the amount of copper used), power dissipation of the DLPC6421 device and power dissipation of surrounding components. The DLPC6421 package is designed primarily to extract heat through the power and ground planes of the PCB, thus copper content and airflow over the PCB are important factors.
The recommended maximum operating ambient temperature (TA) is provided primarily as a design target and is based on maximum DLPC6421 power dissipation and RθJA at 1 m/s of forced airflow, where RθJA is the thermal resistance of the package as measured using a JEDEC defined standard test PCB. This JEDEC test PCB is not necessarily representative of the DLPC6421 PCB, and thus 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. However, after the PCB is designed and the product is built, TI highly recommends that thermal performance be measured and validated.
To do this, the top center case temperature should be measured under the worse case product scenario (max power dissipation, max voltage, max ambient temp) and validated not to exceed the maximum recommended case temperature (TC). This specification is based on the measured φJT for the DLPC6421 package and provides a relatively accurate correlation to junction temperature. Note that care must be taken when measuring this case temperature to prevent accidental cooling of the package surface. TI recommends a small (approx 40 gauge) thermocouple. The bead and the thermocouple wire should contact the top of the package and be covered with a minimal amount of thermally conductive epoxy. The wires should be routed closely along the package and the board surface to avoid cooling the bead through the wires.