AUTOMATION  ANALOG DEVICES


user the ability to adjust the VOUT1 voltage (AD74115H AVDD supply voltage) on-demand. This method minimises power dissipation in the


module under low load conditions particularly in current output modes.


When using the PPC functionality, the host controller in the system sends the required voltage code via SPI to the AD74115H, which is then passed to the ADP1034 via a one-wire serial interface (OWSI). The OWSI has CRC implemented to provide robustness against EMC interference that may be present in harsh industrial environments. If we look at the example power dissipation


calculation, we can see that if AVDD = 24V and the load is 250, for a current output of 20mA, there will be a total of 748mW dissipated in the


module. When we use PPC to drop the AVDD voltage to 8.6V (load voltage + headroom), there is ~348mW dissipated in the module. This reveals a power saving of 400mW within the module.


EXAMPLE POWER DISSIPATION CALCULATION In Example 1 and Example 2, the current output use case is selected and is driving a 20mA output. The load is 250 and the ADC is enabled and converting the default measurement 


Example 1 (No PPC):


• AD74115H Output Power = (AVDD = 24V) × 20mA = 480mW


• AD74115H Input Power =


AD74115HQUIESCENT (206mW) + ADC Power (30mW) + 480mW = 716mW


• Module Input Power = 716mW + ADP1034 Power (132mW) = 848mW


• Load Power = 20mA2 × 250 = 100mW • Total Module Power = (Module Input Power – Load Power) = 748mW


In Example 2, we can see that when the PPC


functionality is enabled to reduce AVDD to the required voltage (20mA × 250) + 3.6V headroom = 8.6V then the power dissipated in the module drops to 348mW.


Figure 3: Power dissipation vs. RLOAD at 20mA output


Figure 4: Power dissipation vs. temperature EXAMPLE 2 (PPC ENABLED):


• AD74115H Output Power = (AVDD = 8.6V) × 20mA = 172mW


• AD74115H Input Power =


AD74115HQUIESCENT (136mW) + ADC Power (30mW) + 172mW = 338mW


Figure 2: Measurement data 20mA into 250 load, AVDD = 24V, AVDD = 8.6V (PPC used)


16 May/June 2025 Irish Manufacturing


• Module Input Power = 338mW + ADP1034 Power (100mW) = 448mW


• Load Power = 20mA2 × 250 = 100mW


• Total Module Power = (Module Input Power – Load Power) = 348mW


Figure 2 shows the measured power dissipated


on the AD74115H applications board at 25°C. The measurement shows the power dissipated is marginally lower than the calculated power dissipation. This will vary slightly from device to device.


Figure 3 shows the module (ADP1034 www.irish-manufacturing.com


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