ADP1720ARMZ-R7 datasheet(12/16 Pages) AD

12 / 16 page

ADP1720

Rev. A | Page 12 of 16

THERMAL CONSIDERATIONS

To guarantee reliable operation, the junction temperature of the

ADP1720 must not exceed 125°C. To ensure the junction tem-

perature 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 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.

Copper Size (mm2)

θJA (°C/W)

118

100

300

500

140

028

VIN – VOUT (V)

1 Device soldered to minimum size pin traces.

The junction temperature of the ADP1720 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 22 to Figure 27 show junction temperature

calculations for different ambient temperatures, load currents,

VIN to VOUT differentials, and areas of PCB copper.

120

100

1mA

5mA

10mA

20mA

30mA

40mA

50mA

(LOAD CURRENT)

MAX TJ (DO NOT OPERATE ABOVE THIS POINT)

Figure 22. 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 23. 100 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 24. 0 mm2 of PCB Copper, TA = 25°C

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