ADP1720TRMZ5-EP-R7 datasheet(10/12 Pages) AD

10 / 12 page

ADP1720-EP

Data Sheet

Rev. A | Page 10 of 12

APPLICATIONS INFORMATION

THERMAL CONSIDERATIONS

To guarantee reliable operation, the junction temperature of

the ADP1720-EP must not exceed 125°C. To ensure that 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 tempera-

ture, 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 on the PCB. Table 5 shows typical θJA values of the

8-lead MSOP package for various PCB copper sizes.

Table 5. Typical θJA Values for ADP1720-EP

Copper Size (mm2)

JA (°C/W)

246

216

100

186

300

178

500

169

The junction temperature of the ADP1720-EP 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 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 that the junction temperature does not rise

above 125°C. Figure 19 to Figure 24 show junction temperature

calculations for different ambient temperatures, load currents,

VIN to VOUT differentials, and areas of PCB copper for the

ADP1720-EP.

140

VIN – VOUT (V)

120

100

1mA

5mA

10mA

20mA

30mA

40mA

50mA

(LOAD CURRENT)

MAX TJ (DO NOT OPERATE ABOVE THIS POINT)

Figure 19. 500 mm2 of PCB Copper, TA = 25°C

140

VIN – VOUT (V)

120

100

1mA

5mA

10mA

20mA

30mA

40mA

50mA

(LOAD CURRENT)

MAX TJ (DO NOT OPERATE ABOVE THIS POINT)

Figure 20. 300 mm2 of PCB Copper, TA = 25°C

140

VIN – VOUT (V)

120

100

1mA

5mA

10mA

20mA

30mA

40mA

50mA

(LOAD CURRENT)

MAX TJ (DO NOT OPERATE ABOVE THIS POINT)

Figure 21. 100 mm2 of PCB Copper, TA = 25°C

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