Maxim-IC Applications Note # AN4456:  Understand Thermal Derating Aspects of PWM ICs to Ensure the Best System Performance

Abstract:

Modern DC-DC converters use PWM controllers with integrated MOSFETs to achieve the highest power density for DC-DC modules. Since the power MOSFETs are inside the PWM chip, they can significantly affect the thermal performance of the device.
For optimal device performance, it is thus critical to establish the thermal-derating aspects of PWM ICs under realistic operating conditions.

This article describes how to construct and calibrate a thermal-derating box for evaluating the thermal performance of PWM controllers.
More: www.maxim-ic.com/AN4456