FE150H datasheet(4/8 Pages) MACOM

4 / 8 page

Tyco Electronics Corp.

Technical Note

August 1997

High-Power Board-Mounted Power Modules

Thermal Mangement for

Basic Thermal Model

Another approach for analyzing thermal performance is

to model the overall thermal resistance of the module.

Total thermal resistance (

θ) is deﬁned as the maximum

case temperature rise (

∆TC, max) divided by the PD of

the module:

where:

θ = total thermal resistance

∆TC, max = maximum case temperature rise

PD = power dissipated as heat

This can be represented by the simpliﬁed model shown

in Figure 9. In this model, PD,

∆TC, max, and θ are

analogous to current ﬂow, voltage drop, and electrical

resistance, respectively, in Ohm’s law.

8-695(C)

Figure 9. Basic Thermal-Resistance Model

For FE-, FC-, and FW-Series 50 W to 200 W BMPMs,

the thermal-resistance value vs. air velocity has been

determined experimentally and is plotted in Figures 10

and 11 for a unit without a heat sink and with six of the

heat sinks mentioned in the previous section. Note that

the highest values on the curves represent natural

convection. In a system with free-ﬂowing air and other

heat sources, there may be additional airﬂow.

8-696(C)

Figure 10. Heat-Sink Resistance Curves; Fins

Oriented Along Width

8-697(C)

Figure 11. Heat-Sink Resistance Curves; Fins

Oriented Along Length

Use an airﬂow measurement just upstream from the

module when determining

θ from these curves (see

Figure 4).

The following examples illustrate how the curves can

be used to determine thermal performance under

various airﬂow and heat-sink conﬁgurations.

Example A. Airﬂow Required to Maintain TC

An FC150A operates at IO = 20 A and TA = 50 °C with

no heat sink. Determine the airﬂow required to maintain

TC, max = 95 °C.

≈ 22.5 W for the FC150A; therefore, the necessary

thermal resistance (

θ) is:

From Figure 10, the required airﬂow is 2.2 m/s (440 ft./min.)

∆TC, max

---------------------

BMPM

= BMPM

THERMAL

RESISTANCE

5.0

4.0

3.0

2.0

1.0

0.0

NAT

CONV

0.5

(100)

1.0

(200)

1.5

(300)

2.0

(400)

2.5

(500)

AIR VELOCITY MEASURED IN m/s (ft./min.)

NO HEAT SINK

0.5 in. HEAT SINK

1 in. HEAT SINK

0.25 in. HEAT SINK

5.0

4.0

3.0

2.0

1.0

0.0

NAT

CONV

0.5

(100)

1.0

(200)

1.5

(300)

2.0

(400)

2.5

(500)

AIR VELOCITY MEASURED IN m/s (ft./min.)

NO HEAT SINK

0.5 in. HEAT SINK

1 in. HEAT SINK

0.25 in. HEAT SINK

TC, max

–

()

-----------------------------------------

–

()

22.5

------------------------

2 °C/W

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