6 Conclusions

After conducting these tests, the final step is to analyze the results. The comparison between the simulations and measurements showed that the results are nearly identical. In general, the simulations predicted that the system would behave worse than what was seen during measurements. Therefore, if the simulations show that the system performs within the acceptable range, then the real system will function as well. The system simulations and measurements showed that a fully functional system using Power over Data Line is possible.

As a reference, the system performance for all topologies was compared to the performance without using PoDL. This was also done for the eight node system. The results of these tests were compared to the corresponding system running PoDL. The result of this comparison showed that the system behavior of the systems using PoDL are very similar to the systems not using PoDL. The systems using PoDL are more susceptible to alien noise, but only by a small margin. This shows that much of the inherent noise of a system stems from the topology and interfaces to the network, both of which affect the system regardless.

While all topologies and component selections that were tested stayed within the required noise margin, clear advantages and disadvantages of each power coupling filter type were discovered. For the filter based on uncoupled single inductors, the resulting system has the lowest noise margin from the filters that were tested. This value degrades even further the lower the value of the inductance, the higher the distance, and the larger the node count become. Filters based on coupled inductors offer a good balance between costs, layout size and noise margin. Coupled inductors have a larger noise margin than separate inductors, but the best performance can be achieved using a filter based on DMCs. Systems using a filter based on DMCs will have the largest noise margin and will therefore be more robust against external noise effects. However, when a large current is required the size and cost of the DMC will greatly increase.

The simulations and tests confirm that DMCs are the most suitable components tested if a large noise margin is required. The tests show that the noise behavior of the system is very close to the behavior without the use of PoDL. However, the simulations and tests showed that some care must be taken in regards to the selection of components. For the power supply filter on each device, at least 80 µH of inductance in total are recommended. For single inductors, this means at least 40 µH on each of the positive and negative wires of the network. The PSE should also support the total power requirements of the system, potentially requiring inductors that have a higher rated current than the powered devices on the network.

Since the possible combinations of power supply voltages, regulators, coupling topology, nominal inductor value and variance, system topology and component vendors is nearly infinite, it is impossible to clearly say which combinations and setups will work. It is vital that simulations are used to assure the functionality of the desired system. This application note shows that with the right model, an entire system can be simulated such that the resulting measurements of a real system are the same as the simulations.

Furthermore, the systems shown here can be viewed as a performance floor. The examples shown here are still functional, so if a new system adheres to the electrical characteristics of its components and the simulations show similar performance to the results presented here, then this new system will also be functional.

An important conclusion to draw from this example is that system simulation is invaluable. It is imperative that the total current and voltage of each component is not exceeded and that the total system noise margin is not wholly consumed by the inherent system noise. The required margin for external noise depends largely on the expected external noise and environmental factors, if the system is expected to be subject to much alien noise then the simulations and topology of the system need to show a larger noise margin for the system to still work in that environment. Early simulation helps detect flaws in the design or topology of a desired system and allows to implement changes early in the design phase.