ADP222ACPZ-1228-R7 datasheet(21/24 Pages) AD

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Data Sheet

ADP222/ADP223/ADP224/ADP225

Rev. B | Page 21 of 24

The junction temperature of the ADP222/ADP223/ADP224/

ADP225 can be calculated by

TJ = TA + (PD × θJA)

(2)

where:

TA is the ambient temperature.

PD is the power dissipation in the die, given by

PD = [(VIN − VOUT) × ILOAD] + (VIN × IGND)

where:

ILOAD is the load current.

IGND is the ground current.

VIN and VOUT are input and output voltages, respectively.

Power dissipation due to ground current is quite small and can

be ignored. Therefore, the junction temperature equation

simplifies to the following:

TJ = TA + {[(VIN − VOUT) × ILOAD] × θJA}

As shown in the simplified equation, for a given ambient

temperature, input- to-output voltage differential, and continuous

load current, there exists a minimum copper size requirement

for the PCB to ensure that the junction temperature does not rise

above 125°C. Figure 72 to Figure 75 show junction temperature

calculations for different ambient temperatures, power dissipation,

and areas of PCB copper.

140

120

100

TOTAL POWER DISSIPATION (W)

0.2

0.4

0.6

0.8

1.0

1.2

6400mm2

1000mm2

500mm2

100mm2

25mm2

JEDEC

TJ MAX

Figure 72. 8-Lead LFCSP, TA = 25°C

140

120

100

TOTAL POWER DISSIPATION (W)

0.2

0.4

0.6

0.8

1.0

1.2

6400mm2

1000mm2

500mm2

100mm2

25mm2

JEDEC

TJ MAX

Figure 73. 8-Lead LFCSP, TA = 50°C

140

120

100

TOTAL POWER DISSIPATION (W)

0.2

0.4

0.6

0.8

1.0

1.2

6400mm2

1000mm2

500mm2

100mm2

25mm2

JEDEC

TJ MAX

Figure 74. 8-Lead LFCSP, TA = 85°C

140

120

100

TOTAL POWER DISSIPATION (W)

TB = 25°C

TB = 50°C

TB = 85°C

TJ MAX

Figure 75. 8-Lead LFCSP, TA = 85°C

In the case where the board temperature is known, use the

thermal characterization parameter, ΨJB, to estimate the

junction temperature rise (see Figure 75). Maximum junction

temperature (TJ) is calculated from the board temperature (TB)

and power dissipation (PD) using the following formula:

TJ = TB + (PD × ΨJB)

(3)

The typical value of ΨJB is 18.2°C/W for the 8-lead LFCSP package.

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