MIC2039 View Datasheet(PDF) - Micrel

Part Name

Description

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MIC2039

High-Accuracy, High-Side, Adjustable Current Limit Power Switch

Micrel 

Micrel, Inc.

Thermal Design

To help reduce the thermal resistance, the ePad

(underneath the IC) should be soldered to the PCB

ground. The placement of thermal vias either underneath

or near the ePad is highly recommended. Thermal

design requires the following application-specific

parameters:

• Maximum ambient temperature (TA)

• Output current (IOUT)

• Input voltage (VIN)

• Current limit (ILIMIT)

When the MIC2039 is in constant current limit mode, it

may exceed the overtemperature threshold. If this

occurs, the overtemperature condition will shut down the

MIC2039 switch and the fault status flag will go active

(assert low). After the switch cools down, it automatically

turns on again. The user can maximize the MIC2039

power dissipation by either lowering the thermal

resistance on the exposed pad (only the DFN package

has an exposed pad) on the printed circuit board, or by

limiting the maximum allowable ambient temperature.

Thermal Measurements

It is always wise to measure the IC’s case temperature

to make sure that it is within its operating limits. Although

this might seem like an elementary task, it is very easy

to get false results. The most common mistake is to use

the standard thermal couple that comes with the thermal

voltage meter. This thermal couple wire gauge is large,

typically 22 gauge, and behaves like a heatsink,

resulting in a lower case measurement.

There are two suggested methods for measuring the IC

case temperature: a thermal couple or an infrared

thermometer. If a thermal couple is used, it must be

constructed of 36 gauge wire or higher to minimize the

wire heatsinking 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 to the case of the IC. Thermal couple

5SC-TT-K-36-36 from Omega is adequate for most

applications.

To avoid using messy thermal couple grease or glue, an

infrared thermometer is recommended. Most infrared

thermometers’ spot size is too large for an accurate

reading on small form factor ICs. However, an IR

thermometer from Optris has a 1mm spot size, which

makes it ideal for the 2mm × 2mm thin DFN package.

Also, get the optional stand. The stand makes it easy to

hold the beam on the IC for long periods of time.

June 7, 2013

15

MIC2039

Revision 1.1

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