FE150H datasheet(7/8 Pages) MACOM

7 / 8 page

Tyco Electronics Corp.

Technical Note

August 1997

High-Power Board-Mounted Power Modules

Thermal Mangement for

Detailed Thermal Model (continued)

Conduction Through a Cold Plate

In some instances, heat can be removed from the top

surface of the module by conduction through a solid

object. One-dimensional conduction heat transfer can

be expressed as:

θ = L/kA

where:

θ = thermal resistance

L = heat travel distance hot to cold (m)

k = material conductivity (W/m • °C)

A = material cross-section area (m2)

For example, an FE150A operating at IO = 30 A and

TA = 40 °C in natural convection is mounted to a copper

base plate that conducts heat to a cooling surface held

at 40 °C (TCs). The base plate cross-section is

0.000806 m2, its length is 0.127 m and k = 380W/m • °C.

From the efﬁciency curves, PD = 33 W. Determine the

case temperature (TC).

The thermal resistance of the base plate is:

θBP = L/kA

θBP = 0.127/(380 • 0.000806)

θBP = 0.4 °C/W

So the overall module resistance is:

θtotal = θother || θBP

θtotal = 1/(1/θother + 1/θBP)

θtotal = 1/(1/8.6 + 1/0.4)

θtotal = 0.4 °C/W

And TC is:

TC = TCs + PD(

θtotal)

TC = 40 + 33(0.4)

TC = 53.2 °C

In this example, thermal resistance from the top sur-

face is low enough that other resistances are negligible

when computing overall resistance.

Operation in Narrow Spaces

Figure 4 shows the typical mounting conﬁguration with

the module oriented vertically in a rectangular pas-

sage. When clearance between the facing board and

the top surface of the module is reduced, airﬂow

between these two surfaces drops, thereby lowering

the heat transfer. This increases the value of

θT. Flow

interference begins when the clearance approaches

the boundary layer thickness on the top surface of the

module. When operating the module in tight spacing,

make a calculation of the boundary layer thickness and

use a higher value of

θT, if necessary, when calculating

θtotal. For assistance, contact a Tyco Application Engi-

neer.

Horizontal Orientation

In some applications, the module is operated in natural

convection and oriented horizontally as shown in

Figure 14. In this situation, use

θtotal = 4.8 °C/W for

overall module thermal resistance.

8-700(C)

Figure 14. Horizontal Orientation

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