MIC7401 datasheet(33/68 Pages) MICREL

33 / 68 page

Micrel, Inc.

MIC7401

March 16, 2015

Revision 1.0

Once the total power dissipation is calculated, the IC

junction temperature can be estimated using Equation 7:

TJ(MAX)

≈ T

A + PD_TOTAL × θJA

Eq. 7

Where:

TJ(MAX) = The maximum junction temperature

TA = The ambient temperature

JA = The junction-to-ambient thermal resistance of the

package (30°C/W)

Figure 16 shows the measured junction temperature

versus power dissipation of the MIC7401 evaluation

board. The actual junction temperature of the IC depends

upon many factors. The significant factors influencing the

die temperature rise are copper thickness in the PCB, the

surface area available for convection heat transfer, air

flow and power dissipation from other components,

including inductors, SOCs and processor ICs. It is good

engineering practice to measure all power components

temperature during the final design review using a

thermal couple or IR thermometer, see the “Thermal

Measurements” sub-section for details.

Figure 16. Power Dissipation

Power Derating

The MIC7401 package has a 2W power dissipation limit.

To keep the IC junction temperature below a 125

⁰C

design limit, the output power has to be limited above an

ambient temperature of 65

°C. Figure 17 shows the power

dissipation derating curve.

Figure 17. Power Derating Curve

The maximum power dissipation of the package can be

calculated by Equation 8:













−

≈

J(MAX)

MAX)

(

Eq. 8

Where:

TJ(MAX) = Maximum junction temperature (125°C)

TA = Ambient temperature

= Junction-to-ambient thermal resistance of the

package (30°C/W).

Overtemperature Fault

An overtemperature fault is triggered when the IC

junction temperature reaches 160°C. When this occurs,

both the over temperature fault flag is set to 1, the global

power good output is pulled low and all the outputs are

turned off. During the fault condition the I²C interface

remains active and all registers values are maintained.

When the die temperature decreases by 20°C the

overtemperature fault bit can be cleared. To clear the

fault, either recycle power or write a logic “0” to the over

temperature fault register. Once the fault bit is cleared,

the outputs power up to their default values and are

sequenced according to the time slot settings.

MIC7401 Datasheet(PDF) 33 Page - Micrel Semiconductor

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