ADFS5758 datasheet(73/75 Pages) AD

73 / 75 page

Data Sheet

ADFS5758

Rev. 0 | Page 73 of 75

APPLICATIONS INFORMATION

Using the example module shown in Figure 94, the module

power dissipation (excluding the power dissipated in the load)

can be calculated using the methodology shown in the Power

Calculation Methodology (RLOAD = 1 kΩ) section. Assuming a

maximum IOUT value of 20 mA and RLOAD value of 1 kΩ, the

total module power is calculated as approximately 226 mW.

Note that power associated with the external digital isolation is

not included in the calculations because this power is dependent

on the choice of component used.

Replacing the 1 kΩ load with a short circuit, the power dissipation

calculation is shown in the Power Calculation Methodology

(RLOAD = 0 Ω) section, which shows that the total module power

becomes approximately 206 mW in a short-circuit load condition.

Power Calculation Methodology (RLOAD = 1 kΩ)

Table 55. Quiescent Current Power Calculation

Voltage (V)

Current (mA)

Power (mW)

AVDD1 = 24

AIDD1 = 0.05

1.2

AVDD2 = 5

AIDD2 = 2.9

14.5

AVSS = −15

AISS = 0.23

3.45

VLOGIC = 3.3

ILOGIC = 0.01

0.033

Using the voltage and current values in Table 55, the total

quiescent current power is 19.18 mW.

Next, perform the following calculation:

(VDPC+) × (20 mA + IDPC+) = 22.5 V × 20.5 mA = 461.25 mW

Assume the dc-to-dc converter is at 90% efficiency. Therefore,

VDPC+ power = 512.5 mW. The total input power at the

ADFS5758 side of the ADP1031 PMU is therefore 512.5 mW +

19.18 mW = 531.68 mW. Subtracting the 400 mW load power

from this value gives the power associated only with the

ADFS5758, which is 131.68 mW.

Assuming an 85% efficiency ADP1031, the total input power

becomes 625.5 mW.

Total Module Power = Input Power − Load Power

Therefore,

625.5 mW − 400 mW = 225.5 mW

Power Calculation Methodology (RLOAD = 0 Ω)

Using the voltage and current values in Table 55, the total

quiescent current power is 19.18 mW.

Next,

(VDPC+) × (20 mA + IDPC+) = 4.95 V × 20.5 mA = 101.5 mW

Assume the dc-to-dc converter at 65% efficiency. Therefore,

VDPC+ power = 156.2 mW. The total input power at the

ADFS5758 side of the ADP1031 is therefore 156.2 mW + 19.18

mW = 175.38 mW. Subtracting the 0 mW load power from this

value gives the power associated only with the ADFS5758,

which is 175.38 mW.

Assuming an 85% efficiency ADP1031, the total input power

becomes 206.33 mW.

Total Module Power = Input Power − Load Power

Therefore,

206.33 mW − 0 mW = 206.33 mW

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