MIC45208 datasheet(21/31 Pages) MICREL

21 / 31 page

Micrel, Inc.

MIC45208

May 29, 2014

Revision 1.2

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)

adequate for most applications.

Wherever

possible,

infrared

thermometer

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 MIC45208 is shown

in Figure 11, Figure 12, Figure 13, Figure 14, and Figure

15.

These

thermal

measurements

were

taken

MIC45208 evaluation board. Since the MIC45208 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 MIC45208.

SOA curves should only be used as a point of reference.

SOA data was acquired using the MIC45208 evaluation

board. Thermal performance depends on the PCB layout,

board size, copper thickness, number of thermal vias,

and actual airflow.

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