MIC28304 Datasheet, PDF (30/39 Pages) Micrel Semiconductor – 70V 3A Power Module

Micrel, Inc.
Table 3. Recommended Component Values for 600kHz Switching Frequency
VOUT
VIN
R1
R11
R3
(Rinj)
(Top Feedback (Bottom Feedback
Resistor)
Resistor)
R19
0.9V 5V to 70V 16.5kΩ
10kΩ
80.6kΩ
DNP
1.2V 5V to 70V 16.5kΩ
10kΩ
20kΩ
DNP
1.8V 5V to 70V 16.5kΩ
10kΩ
8.06kΩ
DNP
2.5V 5V to 70V 16.5kΩ
10kΩ
4.75kΩ
DNP
3.3V 5V to 70V 16.5kΩ
10kΩ
3.24kΩ
DNP
5V 7V to 70V 16.5kΩ
10kΩ
1.9kΩ
DNP
C10
(Cinj)
0.1µF
0.1µF
0.1µF
0.1µF
0.1µF
0.1µF
12V 18V to 70V 23.2kΩ
10kΩ
715Ω
DNP
0.1µF
C12
(Cff)
2.2nF
2.2nF
2.2nF
2.2nF
2.2nF
2.2nF
2.2nF
MIC28304
COUT
47µF/6.3V
or 2 x 22µF
47µF/6.3V
or 2 x 22µF
47µF/6.3V
or 2 x 22µF
47µF/6.3V
or 2 x 22µF
47µF/6.3V
or 2 x 22µF
47µF/6.3V
or 2 x 22µF
47µF/16V
or 2 x 22µF
Thermal Measurements and Safe Operating Area
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 MIC28304 is shown
in the Typical Characteristics − 275kHz Switching
Frequency section. These thermal measurements were
taken on MIC28304 evaluation board. Since the
MIC28304 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 MIC28304.
Emission Characteristics of MIC28304
The MIC28304 integrates switching components in a
single package, so the MIC28304 has reduced emission
compared to standard buck regulator with external
MOSFETS and inductors. The radiated EMI scans for
MIC28304 are shown in the Typical Characteristics
section. The limit on the graph is per EN55022 Class B
standard.
March 25, 2014
30
Revision 1.1