ZHCSGG8F July 2011 – March 2018 LM25118
PRODUCTION DATA.
The highest power dissipating components are the two power MOSFETs, the recirculating diode, and the output diode. The easiest way to determine the power dissipated in the MOSFETs is to measure the total conversion losses (PIN - POUT), then subtract the power losses in the Schottky diodes, output inductor and any snubber resistors. An approximation for the recirculating Schottky diode loss is:
The boost diode loss is:
If a snubber is used, the power loss can be estimated with an oscilloscope by observation of the resistor voltage drop at both turnon and turnoff transitions. The LM25118 package has an exposed thermal pad to aid power dissipation. Selecting diodes with exposed pads will aid the power dissipation of the diodes as well. When selecting the MOSFETs, pay careful attention to RDS(ON) at high temperature. Also, selecting MOSFETs with low gate charge will result in lower switching losses.
See Application Notes AN-1520 A Guide to Board Layout for Best Thermal Resistance for Exposed Packages (SNVA183) and AN-2020 Thermal Design By Insight, Not Hindsight (SNVA419) for thermal management techniques for use with surface mount components.