LTM4680 datasheet(71/132 Pages) AD

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LTM4681

Rev. 0

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APPLICATIONS INFORMATION

If the 60°C ambient temperature is subtracted from the

125°C junction temperature, then the difference of 65°C

divided by 12.8W yields a thermal resistance, θJA, of

5°C/W—in good agreement with the value derived from

thermal simulation shown in the Pin Configuration sec-

tion. Table 10, Table 11 and Table 12 provide equivalent

thermal resistances for 0.9V, 1.5V, and 3.3V outputs with

and without airflow. The derived thermal resistances in

Table 10 through Table 12 for the various conditions can

be multiplied by the calculated power loss as a function

of ambient temperature to derive temperature rise above

ambient, thus maximum junction temperature. Room

temperature power loss can be derived from the efficiency

curves in the Typical Performance Characteristics sec-

tion and adjusted with the above ambient temperature

multiplicative factors.

Table 10 through Table 12: Output Current Derating

Table 10. 0.9V Output

DERATING CURVE

VIN (V)

POWER LOSS CURVE

AIRFLOW (LFM)

HEAT SINK

θJA (°C/W)

Figure 38 to Figure 40

5, 8, 12

Figure 35 to Figure 37

None

Figure 38 to Figure 40

5, 8, 12

Figure 35 to Figure 37

200

None

Figure 38 to Figure 40

5, 8, 12

Figure 35 to Figure 37

400

None

Table 11. 1.5V Output

DERATING CURVE

VIN (V)

POWER LOSS CURVE

AIRFLOW (LFM)

HEAT SINK

θJA (°C/W)

Figure 41 to Figure 43

5, 8, 12

Figure 35 to Figure 37

None

Figure 41 to Figure 43

5, 8, 12

Figure 35 to Figure 37

200

None

Figure 41 to Figure 43

5, 8, 12

Figure 35 to Figure 37

400

None

Table 12. 3.3V Output

DERATING CURVE

VIN (V)

POWER LOSS CURVE

AIRFLOW (LFM)

HEAT SINK

θJA (°C/W)

Figure 44 to Figure 46

5, 8, 12

Figure 35 to Figure 37

None

Figure 44 to Figure 46

5, 8, 12

Figure 35 to Figure 37

200

None

Figure 44 to Figure 46

5, 8, 12

Figure 35 to Figure 37

400

None

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