Before proceeding, please ensure you have the DEMO_AD5758-AO8Z Demo software installed on your PC or Laptop and that the latest version of the firmware has been uploaded to the board. Instructions on how to complete these steps can be found earlier in this guide in the Software Details section.
If either P4 and/or P5 jumpers are inserted, then there will be no isolation between the system domain and the field power domain.
Resistor values between 0 Ω and 1 kΩ can be used. However, lower values provide a more challenging load and demonstrate the DPC mode power savings better.
When DPC mode is turned off, the DPC buck is programmed to output a fixed voltage of 23.3 V. Because the load resistance is low (1 Ω), there is a large voltage drop across the AD5758 output buffer. There is 23.3V X 20mA = 466mW of power dissipated in the output buffer plus an additional 47 mW dissipation in the DPC buck regulator
(466 mW X (1-η)). Which translates to 513 mW of dissipation per channel in the module.
Notice how VDPC+ is now at its minimum value of approximately 4.95 V and the die temperature begins to drop rapidly as DPC power saving take effect.
When DPC mode is turned on, a high efficiency (η = 0.9) buck converter reduces the supply to the buffer to 2.5 V above the required output voltage or 4.95 V - whichever is higher, so there is now a small voltage drop of only 4.95 V across the AD5758 output buffer1. This translates to 4.95V X 20mA = 99mW plus 99 mW X (1 - η) = 10 mW of heat dissipation in the output buffer of the AD5758. This is a power saving of 404 mW per channel.
1 If VIOUT > 2.5 V, then the the DPC buck tracks the output to maintain a fixed 2.5 V headroom.