MIC45212 Datasheet, PDF (21/31 Pages) Micrel Semiconductor – 26V/14A DC-to-DC Power Module

Micrel, Inc.
Thermal Measurements and Safe Operating Area
(SOA)
Measuring the IC’s case temperature is recommended to
ensure it is within its operating limits. Although this might
seem like a very elementary task, it is easy to get
erroneous results. The most common mistake is to use
the standard thermal couple that comes with a thermal
meter. This thermal couple wire gauge is large, typically
22 gauge, and behaves like a heatsink, resulting in a
lower case measurement.
Two methods of temperature measurement are using a
smaller thermal couple wire or an infrared thermometer. If
a thermal couple wire is used, it must be constructed of
36-gauge wire or higher (smaller wire size) to minimize
the wire heat-sinking effect. In addition, the thermal
couple tip must be covered in either thermal grease or
thermal glue to make sure that the thermal couple
junction is making good contact with the case of the IC.
Omega brand thermal couple (5SC-TT-K-36-36) is
adequate for most applications.
Wherever possible, an infrared thermometer is
recommended. The measurement spot size of most
infrared thermometers is too large for an accurate
reading on a small form factor ICs. However, an IR
thermometer from Optris has a 1mm spot size, which
makes it a good choice for measuring the hottest point on
the case. An optional stand makes it easy to hold the
beam on the IC for long periods of time.
The safe operating area (SOA) of the MIC45212 is shown
in Figure 11, Figure 12, Figure 13, Figure 14, and Figure
15. These thermal measurements were taken on
MIC45212 evaluation board. Since the MIC45212 is an
entire system comprised of switching regulator controller,
MOSFETs and inductor, the part needs to be considered
as a system. The SOA curves will give guidance to
reasonable use of the MIC45212.
SOA curves should only be used as a point of reference.
SOA data was acquired using the MIC45212 evaluation
board. Thermal performance depends on the PCB layout,
board size, copper thickness, number of thermal vias,
and actual airflow.
April 28, 2014
21
MIC45212
Revision-1.0