Thermal Performance of the LM3404/04HV in SO-8 and PSOP-8 Packages

The first part of this application note will explore the performance of the LM3404HV in a high current, high input voltage, high duty cycle application typical of many LED drivers, using lab-tested thermal performance results and simulations. The industry standard SO-8 package and the pin-for-pin compatible PSOP-8 package with an exposed thermal pad (also called a die-attach paddle, or DAP) will be compared to help the user estimate the die temperature under various conditions, and determine which package is best for their application.

The second part of this application note uses the power dissipation calculated in the first section to estimate the LM3404HV’s die temperature under two typical configurations of the LEDs relative to the LED driver. The first case is for the LM3404HV mounted on a separate PCB that is connected to the LEDs by a wiring harness. This case assumes an ambient temperature influenced by the heating of the LEDs, but no direct heating of the PCB by the LEDs themselves. The second case assumes the LM3404HV is mounted to the same MCPCB as the LEDs themselves. In this configuration the temperature of the MCPCB has a much stronger influence over the LM3404HV die temperature than the ambient temperature, and the tests assume a fixed MCPCB temperature instead of a fixed ambient temperature.