MIC5166 datasheet(14/25 Pages) MICREL

14 / 25 page

Micrel, Inc.

MIC5166

June 2012

M9999-060612-A

First, calculate the power dissipation of the regulator

from these numbers and the device parameters from this

datasheet.

PD = (VIN – VTT) × IOUT + (VBIAS × IGND)

Eq. 1

where the ground current is approximated by using

numbers from the “Electrical Characteristics” or “Typical

Characteristics.”

For example, given an expected maximum ambient

temperature (TA) of 70°C with VIN = 1.2V, VBIAS = 3.3V,

VTT = 0.9V, and IOUT = 3A, first calculate the expected PD

using Equation 1:

PD = (1.2V – 0.9V) × 3A + 3.3V × 0.0016A

= 0.90528W

Eq. 2

Next, determine the junction temperature for the

expected power dissipation above using the thermal

resistance (θJA) of the 10-pin 3mm × 3mm MLF

® (YML)

adhering to the following criteria for the PCB design

(1oz.

copper

and

100mm

copper

area

for

the MIC5166):

TJ = (θJA × PD) + TA = (60.7°C/W × 0.90528W) + 70°C

= 124.95

°C

Eq. 3

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 70

°C:

PD(MAX) = (TJ(MAX) – TA)/θJA = (125°C – 70°C)/(60.7°C/W)

= 0.9061W

Eq. 4

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 thermocouple that comes

with the thermal voltage meter. This thermocouple 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 thermocouple or an infrared

thermometer. If a thermocouple is used, it must be

constructed of 36 gauge wire or higher to minimize the

wire heatsinking effect. In addition, the thermocouple tip

must be covered in either thermal grease or thermal glue

to make sure that the thermocouple junction is making

good contact to the case of the IC. This thermocouple

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

applications.

To avoid this messy thermocouple 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 3mm x 3mm MLF

® package.

MIC5166 Datasheet(PDF) 14 Page - Micrel Semiconductor

MIC5166 Datasheet(HTML) 14 Page - Micrel Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Datasheet Download

Link URL