ADP172ACBZ-2.1-R7 datasheet(14/17 Pages) AD

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Data Sheet

ADP172

APPLICATIONS INFORMATION

analog.com

Rev. F | 14 of 17

typical θJA values of the 4-ball WLCSP package for various PCB

copper sizes.

Table 6. Typical θJA Values

Copper Size (mm2)

θJA (°C/W)

260

159

100

157

300

153

500

151

1 Device soldered to minimum size pin traces.

The junction temperature of the ADP172 can be calculated from the

following equation:

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 (3)

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 (4)

As shown in Equation 4, 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 30

to Figure 35 show junction temperature calculations for different

ambient temperatures, load currents, VIN to VOUT differentials, and

areas of PCB copper.

Figure 30. 500 mm2 of PCB Copper, TA = 25°C

Figure 31. 100 mm2 of PCB Copper, TA = 25°C

Figure 32. 0 mm2 of PCB Copper, TA = 25°C

Figure 33. 500 mm2 of PCB Copper, TA = 50°C

Figure 34. 100 mm2 of PCB Copper, TA = 50°C

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