MIC26903ZA Datasheet, PDF (21/28 Pages) Micrel Semiconductor – 28V, 9A Hyper Speed Control Synchronous DC/DC Buck Regulator

Micrel, Inc.
Figure 8. Voltage-Divider Configuration
In addition to the external ripple injection added at the FB
pin, internal ripple injection is added at the inverting input
of the comparator inside the MIC26903-ZA, as shown in
Figure 9. The inverting input voltage V_INJ is clamped to
1.2V. As V_OUT increases, the swing of V_INJ is clamped.
The clamped V_INJ reduces the line regulation because it is
reflected as a DC error on the FB terminal. Therefore, the
maximum output voltage of the MIC26903-ZA should be
limited to 5.5V to avoid this problem.
MIC26903-ZA
Thermal Measurements
Measuring the IC’s case temperature is recommended to
ensure that it is within its operating limits. Although this
might seem like an elementary task, it is easy to get false
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.
Figure 9. Internal Ripple Injection
May 29, 2013
21
Revision 1.0