ADP1712AUJZ-2.5-R71 datasheet(13/16 Pages) AD

13 / 16 page

ADP1712/ADP1713/ADP1714

Rev. A | Page 13 of 16

THERMAL CONSIDERATIONS

To guarantee reliable operation, the junction temperature of the

ADP1712/ADP1713/ADP1714 must not exceed 125°C. To

ensure the junction temperature 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 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 pin of the package

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

5lead TSOT package for various PCB copper sizes.

Table 5.

Copper Size (mm2)

θJA

(°C/W)

170

152

100

146

300

134

500

131

1 Device soldered to minimum size pin traces.

The junction temperature of the ADP1712/ADP1713/ADP1714

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 the ground current.

VIN and VOUT are input voltage and output voltage, 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 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 the junction temperature does not rise above 125°C. The

following figures show junction temperature calculations for

different ambient temperatures, load currents, input-to-output

voltage differentials, and areas of PCB copper.

140

0.5

5.0

VIN – VOUT (V)

120

100

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

1mA

10mA

30mA

80mA

100mA

200mA

300mA

(LOAD CURRENT)

MAX TJ (DO NOT OPERATE ABOVE THIS POINT)

Figure 33. 500 mm2 of PCB Copper, TA = 25°C

140

0.5

5.0

VIN – VOUT (V)

120

100

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

1mA

10mA

30mA

80mA

100mA

200mA

300mA

(LOAD CURRENT)

MAX TJ (DO NOT OPERATE ABOVE THIS POINT)

Figure 34. 100 mm2 of PCB Copper, TA = 25°C

140

0.5

5.0

VIN – VOUT (V)

120

100

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

1mA

10mA

30mA

80mA

100mA

200mA

300mA

(LOAD CURRENT)

MAX TJ (DO NOT OPERATE ABOVE THIS POINT)

Figure 35. 0 mm2 of PCB Copper, TA = 25°C

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