LTM8049 datasheet(13/20 Pages) LINER

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LTM4661

4661f

For more information www.linear.com/LTM4661

curves. The junctions are maintained at 110°C maximum

while lowering output current or power with increasing

ambient temperature. The decreased output current will

decrease the internal module loss as ambient temperature

isincreased.Themonitoredjunctiontemperatureof110°C

minus the ambient operating temperature specifies how

much module temperature rise can be allowed. As an ex-

ample, in Figure 13 the load current is derated to ~0.35A

at ~80°C with no air or heat sink and the power loss for

the 3.3V to 15V at 0.35A output is about 1.4W. The 1.4W

loss is calculated with the ~1.0W room temperature loss

from the 3.3V to 15V power loss curve at 0.35A, and the

1.4 multiplying factor. If the 80°C ambient temperature

is subtracted from the 110°C junction temperature, then

the difference of 30°C divided by 1.4W equals a 21.4°C/W

θJA thermal resistance. Table 3 specifies a 21°C/W value

which is very close. Table 3 to Table 6 provide equivalent

thermal resistances for 5V, 8V, 12V and 15V outputs with

and without airflow and heat sinking. The derived thermal

resistances in Tables 3 to 6 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 section

and adjusted with the above ambient temperature mul-

tiplicative factors. The printed circuit board is a 1.6mm

thick four layer board with two ounce copper for the two

outer layers and one ounce copper all four layers. The

PCB dimensions are 65mm × 65mm.

APPLICATIONS INFORMATION

Figure 4. 5V Output Power Loss

Figure 5. 8V Output Power Loss

Figure 6. 12V Output Power Loss

Figure 7. 15V Output Power Loss

Figure 8. 3.3V to 5V Derating

Curve, No Heat Sink

Figure 9. 3.3V to 8V Derating

Curve, No Heat Sink

LOAD CURRENT (A)

0.2

1.8

1.4

0.6

1.6

1.2

2.8

2.4

2.6

2.2

0.8

0.4

1.8

0.6

1.4

4661 F04

0.8

1.6

0.4

1.2

0.2

3.3V INPUT

LOAD CURRENT (A)

0.2

1.8

1.4

0.6

1.6

1.2

0.8

0.4

1.8

0.6

1.4

4661 F05

0.8

1.6

0.4

1.2

0.2

3.3V INPUT

5V INPUT

AMBIENT TEMPERATURE (°C)

2.5

1.5

0.5

100

4661 F08

110

0LFM

200LFM

400LFM

LOAD CURRENT (A)

0.2

1.8

1.4

0.6

1.6

1.2

0.8

0.4

0.5

0.9

0.3

0.7

4661 F06

0.4

0.8

0.2

0.6

0.1

3.3V INPUT

5V INPUT

AMBIENT TEMPERATURE (°C)

1.2

0.8

0.2

0.4

0.6

100

4661 F09

110

0LFM

200LFM

400LFM

LOAD CURRENT (A)

0.2

1.8

1.4

0.6

1.6

1.2

0.8

0.4

0.5

0.9

0.3

0.7

4661 F07

0.4

0.8

0.2

0.6

0.1

3.3V INPUT

5V INPUT

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