AD5758 datasheet(70/72 Pages) AD

70 / 72 page

AD5758

Data Sheet

Rev. 0 | Page 70 of 72

APPLICATIONS INFORMATION

EXAMPLE MODULE POWER CALCULATION

Using the example module shown in Figure 93, 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 51. 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 51, 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 AD5758

side of the isolated dc-to-dc power module 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

AD5758, which is 131.68 mW.

Assuming an 85% efficiency isolated, dc-to-dc power module,

the total input power becomes 625.5 mW (see Figure 93).

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 51, the total

quiescent current power is 19.18 mW.

Next,

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

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

power = 156.2 mW. The total input power at the AD5758 side of

the isolated dc-to-dc power module 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

AD5758, which is 175.38 mW.

Assuming an 85% efficiency isolated, dc-to-dc power module,

the total input power becomes 206.33 mW (see Figure 93).

Total Module Power

= Input Power − Load Power

Therefore,

206.33 mW − 0 mW = 206.33 mW

AVSS

AVDD1

AVDD2

VDPC+

LDO

DC-TO-DC

CIRCUITRY

OUTPUT

CIRCUITRY

+5V

–15V

+24V

+3.3V

VIOUT

R LOAD

AD5758

ADuCM3029

ISOLATED

DC-TO-DC

POWER

MODULE

(85% EFFICIENCY)

+5V

–15V

+24V

+24V RAIL

(1) TOTAL INPUT POWER

(2) LOAD POWER

(3) TOTAL MODULE POWER

Figure 93. Example Module Containing AD5758

AD5758 Datasheet(PDF) 70 Page - Analog Devices

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