ADP1715ARMZ-R7 datasheet(13/20 Pages) AD

13 / 20 page

ADP1715/ADP1716

Rev. 0 | Page 13 of 20

should be aware of the parameters that contribute to junction

temperature changes. These parameters include ambient

temperature, power dissipation in the power device, and thermal

resistances between the junction and ambient air (θJA). The θJA

number is dependent on the package assembly compounds used

and the amount of copper to which the GND pins of the package

are soldered to on the PCB. Table 5 shows typical θJA values of the

8-lead thermally enhanced MSOP package for various PCB

copper sizes.

Table 5.

Copper Size (mm2)

θJA (°C/W)

118

100

300

500

700

1 Device soldered to minimum size pin traces.

The junction temperature of the ADP1715/ADP1716 can be

calculated from the following equation:

TJ = TA + (PD × θJA)

(3)

where:

TA is the ambient temperature.

PD is the power dissipation in the die, given by

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

(4)

where:

ILOAD is the load current.

IGND is 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}

(5)

As shown in Equation 5, 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 the junction temperature does not rise above 125°C. The

following figures show junction temperature calculations for

different ambient temperatures, load currents, VIN to VOUT

differentials, and areas of PCB copper.

140

VIN – VOUT (V)

120

100

1mA

10mA

50mA

100mA

250mA

360mA

500mA

(LOAD CURRENT)

DO NOT OPERATE ABOVE THIS POINT

MAX TJ

Figure 34. 700 mm2 of PCB Copper, TA = 25°C

140

VIN – VOUT (V)

120

100

1mA

10mA

50mA

100mA

250mA

360mA

500mA

(LOAD CURRENT)

DO NOT OPERATE ABOVE THIS POINT

MAX TJ

Figure 35. 300 mm2 of PCB Copper, TA = 25°C

140

VIN – VOUT (V)

120

100

1mA

10mA

50mA

100mA

250mA

360mA

500mA

(LOAD CURRENT)

DO NOT OPERATE ABOVE THIS POINT

MAX TJ

Figure 36. 100 mm2 of PCB Copper, TA = 25°C

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