LTC2977 datasheet(78/138 Pages) AD

78 / 138 page

LTM4664A

Rev. 0

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thermal resistances in Table 10 and Table 11 are 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 multiplicative factors.

Thermal performance expectations at up to 60A output (at

up to 1.2VOUT) can be suitably approximated by studying

this section's figures at analogous nearby output power

conditions. For example: 1.2VOUT at 60A is 72W output.

For thermal purposes, this operating point can be approx-

imated by 1.5VOUT at 48A output (observe: also 72W out-

put). The 1.5VOUT curves shown in this section can thus

be utilized to infer thermal performance at currents higher

than 25A, per channel (for output voltages up to 1.2VOUT).

TABLE 10 AND TABLE 11: OUTPUT CURRENT DERATING (BASED ON DEMO BOARD)

Table 10. 1.0V Output

DERATING CURVE

VIN (V)

POWER LOSS CURVE

AIRFLOW (LFM)

HEAT SINK

θJA (°C/W)

Figure 41, 42

48, 54

Figure 39, 40

None

5.3

Figure 41, 42

48, 54

Figure 39, 40

200

None

4.5

Figure 41, 42

48, 54

Figure 39, 40

400

None

4.0

Table 11. 1.5V Output

DERATING CURVE

VIN (V)

POWER LOSS CURVE

AIRFLOW (LFM)

HEAT SINK

θJA (°C/W)

Figure 43, 44

48, 54

Figure 39, 40

None

5.3

Figure 43, 44

48, 54

Figure 39, 40

200

None

4.5

Figure 43, 44

48, 54

Figure 39, 40

400

None

4.0

DUAL 25A/30A PSM APPLICATIONS INFORMATION

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