LTM4627EVPBF datasheet(18/28 Pages) LINER

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LTM4627

4627f

Figure 7. 1.2VOUT Power Loss

Figure 8. 3.3VOUT Power Loss

0.5

1.5

4627 F07

2.0

3.0

2.5

1.0

0 12 3 4 5 6

9 10 11 12 13 14 15

OUTPUT CURRENT (A)

5VIN TO 1.2VOUT POWER LOSS

12VIN TO 1.2VOUT POWER LOSS

4627 F08

0 12 3 4 5 6 7 8 9 10 11 12 13 14 15

OUTPUT CURRENT (A)

5VIN TO 3.3VOUT POWER LOSS

12VIN TO 3.3VOUT POWER LOSS

APPLICATIONS INFORMATION

Figure 10. 5VIN to 1.2VOUT with Heat Sink

4627 F10

0 LFM

200 LFM

400 LFM

90 100 110 120 130

AMBIENT TEMPERATURE (°C)

Figure 9. 5VIN to 1.2VOUT No Heat Sink

4627 F09

0 LFM

200 LFM

400 LFM

90 100 110 120 130

AMBIENT TEMPERATURE (°C)

nal module loss as ambient temperature is increased.

The monitored junction temperature of 120°C minus

the ambient operating temperature speciﬁes how much

module temperature rise can be allowed. As an example in

Figure 11 the load current is derated to ~12A at ~80°C with

no air or heat sink and the power loss for the 12V to 1.2V

at 12A output is about 2.8W. The 2.8W loss is calculated

with the ~2.35W room temperature loss from the 12V to

1.2V power loss curve at 12A, and the 1.2 multiplying

factor at 80°C ambient. If the 80°C ambient temperature

is subtracted from the 120°C junction temperature, then

the difference of 40°C divided by 2.8W equals a 14°C/W

θJA thermal resistance. Table 2 speciﬁes a 13°C/W value

which is very close. Table 2 and Table 3 provide equivalent

thermal resistances for 1.2V and 3.3V outputs with and

without airﬂow and heat sinking. The derived thermal re-

sistances in Tables 2 and 3 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 multipli-

cative 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 for the two inner layers. The

PCB dimensions are 95mm

× 76mm. The BGA heat sinks

are listed in Table 4.

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