MIC61300 datasheet(14/22 Pages) MICREL

14 / 22 page

Micrel, Inc.

MIC61300

September 2010

M9999-092910-A

To determine the maximum power dissipation allowed

that would not exceed the IC’s maximum junction

temperature (125

°C) when operating at a maximum

ambient temperature of 75

°C by:

PD(MAX) = (TJ(MAX) – TA) / θJA

= (125

°C − 75°C) / (60.7°C/W)

= 0.824W

Eq. 6

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 a very elementary task, it is very

easy to get erroneous 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. This thermal couple

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

applications.

To avoid this messy thermal couple grease or glue, an

infrared thermometer is recommended. Most infrared

thermometers’ spot size are 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 3mm

× 3mm MLF® package. Also,

get the optional stand. The stand makes it easy to hold

the beam on the IC for long periods of time.

Enable

The MIC61300 features an active high enable input (EN)

that allows ON/OFF control of the regulator. The current

through the device reduces to near “zero” when the

device is shutdown, with only microamperes of leakage

current. The EN input may be directly tied to VIN or

driven by a voltage that is higher than VIN as long as the

voltage does not exceed the maximum operating rating

of the EN pin.

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