ADP1763ACPZ0.95-R7 datasheet(16/19 Pages) AD

16 / 19 page

Data Sheet

ADP1763

Rev. 0 | Page 15 of 18

Use Equation 5 to calculate the output of the two paralleled

ADP1763 LDOs.

VOUT = 2 × AD × (RADJ × IADJ)

(5)

where:

AD is the gain factor with a typical value of 3.0 between the

VADJ pin and the VOUT pin.

IADJ is the 50.0 μA constant current out of the VADJ pin.

THERMAL CONSIDERATIONS

To guarantee reliable operation, the junction temperature of the

ADP1763 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 temperature, power

dissipation in the power device, and thermal resistance between

the junction and ambient air (θJA). The θJA value is dependent

on the package assembly compounds used and the amount of

copper to which the GND pin and the exposed pad (EPAD) of the

package are soldered on the PCB. Table 7 shows typical θJA values

for the 16-lead LFCSP for various PCB copper sizes. Table 8

shows typical ΨJB values for the 16-lead LFCSP.

Table 7. Typical θJA Values

Copper Size (mm2)

θJA (°C/W), LFCSP

138.1

100

102.9

500

76.9

1000

67.3

6400

Table 8. Typical ΨJB Values

Copper Size (mm2)

ΨJB (°C/W) at 1 W

100

33.3

500

28.9

1000

28.5

To calculate the junction temperature of the ADP1763, use the

following equation:

TJ = TA + (PD × θJA)

(6)

where:

TA is the ambient temperature.

PD is the power dissipation in the die, given by

PD = ((VIN − VOUT) × ILOAD) + (VIN × IGND)

(7)

where:

VIN and VOUT are the input and output voltages, respectively.

ILOAD is the load current.

IGND is the ground current.

As shown in Equation 6, for a given ambient temperature, and

computed power dissipation, a minimum copper size

requirement exists for the PCB to ensure that the junction

temperature does not rise above 125°C.

Figure 35 through Figure 40 show junction temperature calculations

for different ambient temperatures, load currents, VIN to VOUT

differentials, and areas of PCB copper.

VIN – VOUT (V)

100

120

140

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

TJ MAX

500mA

10mA

100mA

Figure 35. 6400 mm2 of PCB Copper, TA = 25°C

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

VIN – VOUT (V)

100

120

140

500mA

10mA

100mA

TJ MAX

Figure 36. 500 mm2 of PCB Copper, TA = 25°C

TJ MAX

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

VIN – VOUT (V)

100

120

140

500mA

10mA

100mA

Figure 37. 25 mm2 of PCB Copper, TA = 25°C

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