ADP2140 datasheet(28/32 Pages) AD

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ADP2140

Data Sheet

Rev. B | Page 28 of 32

THERMAL CONSIDERATIONS

In most applications, the ADP2140 does not dissipate much

heat due to its high efficiency. However, in applications with

high ambient temperature and high supply voltage-to-output

voltage differential, the heat dissipated in the package is large

enough that it can cause the junction temperature of the die to

exceed the maximum junction temperature of 125°C.

When the junction temperature exceeds 150°C, the converter

enters thermal shutdown. It recovers only after the junction

temperature has decreased below 130°C to prevent any permanent

damage. Therefore, thermal analysis for the chosen application

is very important to guarantee reliable performance over all

conditions. The junction temperature of the die is the sum of

the ambient temperature of the environment and the tempera-

ture rise of the package due to the power dissipation, as shown

in Equation 2.

To guarantee reliable operation, the junction temperature of the

ADP2140 must not exceed 125°C. To ensure the junction temper-

ature stays below this maximum value, the user needs to be aware

of the parameters that contribute to junction temperature changes.

These parameters include ambient temperature, power dissipa-

tion in the power device, and thermal resistances between the

junction and ambient air (θJA). The θJA number is dependent on

the package assembly compounds that are used and the amount of

copper used to solder the package GND pins to the PCB. Table 10

shows typical θJA values of the 10-lead, 3 mm × 3 mm LFCSP for

various PCB copper sizes.

Table 10. Typical θJA Values

Copper Size (mm2)

θJA (°C/W)

42.5

40.0

100

38.8

300

37.2

500

36.2

1 The device is soldered to minimum size pin traces.

The junction temperature of the ADP2140 can be calculated

from the following equation:

TJ = TA + (PD × θJA)

(2)

where:

TA is the ambient temperature.

PD is the total power dissipation in the die, given by

PD = PLDO + PBUCK

where:

PLDO = [(VIN − VOUT) × ILOAD] + (VIN × IAGND)

(3)

PBUCK = PSW + PTRAN + PSW_COND

(4)

where:

ILOAD is the LDO load current.

IAGND is the analog ground current.

VIN and VOUT are the LDO input and output voltages,

respectively.

PSW, PTRAN, and PSW_COND are defined in the Efficiency section.

For a given ambient temperature and total power dissipation,

there exists a minimum copper size requirement for the PCB to

ensure the junction temperature does not rise above 125°C. The

following figures show junction temperature calculations for

different ambient temperatures, total power dissipation, and

areas of PCB copper.

145

135

125

115

105

0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00

TOTAL POWER DISSIPATION (W)

500mm2

50mm2

0mm2

TJ MAX

Figure 91. Junction Temperature vs. Power Dissipation, TA = 25°C

140

130

120

110

100

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

2.25

2.50

TOTAL POWER DISSIPATION (W)

500mm2

50mm2

0mm2

TJ MAX

Figure 92. Junction Temperature vs. Power Dissipation, TA = 50°C

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