MIC28304 datasheet(30/39 Pages) MICREL

30 / 39 page

Micrel, Inc.

MIC28304

Table 3. Recommended Component Values for 600kHz Switching Frequency

VOUT

VIN

(Rinj)

(Top Feedback

Resistor)

R11

(Bottom Feedback

Resistor)

R19

C10

(Cinj)

C12

(Cff)

COUT

0.9V

5V to 70V

16.5kΩ

10kΩ

80.6kΩ

DNP

0.1µF

2.2nF

47µF/6.3V

or 2 x 22µF

1.2V

5V to 70V

16.5kΩ

10kΩ

20kΩ

DNP

0.1µF

2.2nF

47µF/6.3V

or 2 x 22µF

1.8V

5V to 70V

16.5kΩ

10kΩ

8.06kΩ

DNP

0.1µF

2.2nF

47µF/6.3V

or 2 x 22µF

2.5V

5V to 70V

16.5kΩ

10kΩ

4.75kΩ

DNP

0.1µF

2.2nF

47µF/6.3V

or 2 x 22µF

3.3V

5V to 70V

16.5kΩ

10kΩ

3.24kΩ

DNP

0.1µF

2.2nF

47µF/6.3V

or 2 x 22µF

7V to 70V

16.5kΩ

10kΩ

1.9kΩ

DNP

0.1µF

2.2nF

47µF/6.3V

or 2 x 22µF

12V

18V to 70V

23.2kΩ

10kΩ

715Ω

DNP

0.1µF

2.2nF

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)

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 MIC28304 is shown

in the Typical Characteristics

− 275kHz Switching

Frequency section. These thermal measurements were

taken

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

Revision 1.1

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