New PMICs Leverage Maximum Power Point Tracking for Energy Harvesting
Recently, energy harvesting technology has become more and more prevalent. What are the basics of it and what new PMICs are making waves?
In the budding field of IoT, design for maximum battery life is amongst the top priority for engineers. One popular way to achieve this is to leverage on-device energy harvesting via solar or RF energy sources. While improvements in the harvesting devices' efficiencies usually get the most coverage, these systems are equally important to these systems: the power management ICs (PMICs) that get employed.
An example energy harvesting system. Image from Mouser
This past month has seen activity in the energy harvesting PMIC market, with new both from e-peas and from Nowi. This article discusses some attributes of PMICs for energy harvesting applications and discusses the field developments.
PMICs for Energy Harvesting
Energy harvesting systems impose some unique requirements on the underlying power management circuitry, creating a demand for specialized PMICs explicitly designed for the application.
One aspect of energy harvesting that is unique is that they are typically working very low voltages. A single-cell photovoltaic (PV), for example, has a standard output of 0.8 V. In contrast, a Li-ion battery tends to have a cell voltage of 4.2 V. As such, an essential metric for energy harvesting.
Another unique attribute is the PMIC's ability to cleanly and efficiently boost low voltages and how low they can start from, known as cold start.
A design challenge for energy harvesting PMICs is the highly non-linear output of sources like solar cells. Image from Digi-Key
The second intricacy of energy harvesting is the fact that they deal with inconsistent energy sources. Whereas many standard PMICs are designed to work with constant sources, like a battery, an energy harvester's output will fluctuate significantly throughout the day. For this reason, a metric of energy harvesting PMICs is Maximum Power Point Tracking (MPPT).
MPPT is a technique where the PMIC dynamically adapts itself based on its present inputs to ensure maximal average power output to the storage device over time. Its efficacy is typically measured based on how quickly the MPPT algorithm responds to input changes. A good PMIC could adjust within seconds, with some capable of adapting in a fraction of a second.
The Newest PMIC from e-peas
Now that some background has been established for energy harvesting devices, one company shaking up the realm with its PMICs is e-peas. Recently, e-peas has released three new PMICs, the AEM10900, AEM10300, and AEM30300.
These PMICs have some impressive operational characteristics; notably, all three claim to draw no quiescent current from the battery, ensuring the precious stored energy isn't wasted on the PMIC. Whether they have a true "zero" quiescent current or have such a small draw that it's considered negligible is yet to be seen, but regardless this is an impressive feat.
A typical application diagram for the AEM10900. Image from e-peas
The AEM10900, which is more focused on solar harvesting, works with a cold start voltage of 250 mV, an impressively low number. The AEM10300 and AEM30300, which both seem to focus on RF harvesting, offer extremely low-power DC/DC converters with the capability to boost voltages in a range of 100 mV to 4.5 V.
All three devices feature MPPT functionality and can draw input power in the single-digit microwatts given the configuration.
Though e-peas has been fairly active with its energy harvesting PMICs, another company trying to make waves with its tech is Nowi.
Nowi Teams Up with Remote Solution
The companies say that this collaboration is an effort in sustainability, where Remote Solution desires to bring energy harvesting to its devices to minimize battery-related landfills. To this end, the company has chosen to work with Nowi for its NH2 PMICs.
According to Nowi, the NH2 provides Remote Solutions with a small BOM and footprint, only requiring a single external capacitor to function and having a footprint of 12 mm2. Moreso, Nowi brags about its NH2's MPPT capabilities, which is said to have a 1s response time to changes in its environment.
Both Nowi and e-peas seem to clearly know their target audience and applications, as their products check all the right boxes and focus on all the right metrics. As the progression towards battery-free and sustainable energy IoT applications keeps growing, the number of new PMICs and energy harvesting as a whole is sure to keep advancing.
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