MIC22405 Datasheet, PDF (19/30 Pages) Micrel Semiconductor – 4A Integrated Switch High-Efficiency Synchronous Buck Regulator

Micrel, Inc.
Thermal Measurements
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 heat-sink, resulting in a
lower case measurement.
Two better 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 then (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.
Whenever 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.
Sequencing and Tracking
There are four variations which are easily implemented
using the MIC22405. The two sequencing variations are
Delayed and Windowed. The two tracking variants are
Normal and Ratio Metric. The following diagrams
illustrate methods for connecting two MIC22405’s to
achieve these requirements.
Window Sequencing:
MIC22405
June 2011
Time (4.0ms/div)
19
M9999-061511-A