This week’s EYE ON NPI (video) is enjoying the beautiful weather with you, whether sitting in the sun or lounging in the shade – all’s good because we’ve got Nexperia’s NEH2000BY Energy Harvesting Power Management IC with embedded solar MPPT capability!
This tiny, low-cost chip is a one-stop solution for extending the life of your product by making it powered by small solar cells.
This chip is perfect for wearables or miniature sensor nodes, maybe with a LoRa radio, WiFi or Bluetooth Low Energy where space and pricing is important. For example, an asset tracker, traffic monitor, activity watch, or agricultural sensor network: stuff that is outside anyways so it’ll be designed for outdoor use and have lots of sun exposure.
We’ve covered other MPPT tracking solar harvesting chips, and the NEH2000BY has some advantages in size, cost and simplicity. Either use it to increase the time between charges, or use it to have your product be fully encased with no need for charging at all, thanks to the power of the SUN.
The Nexperia NEH2000BY energy harvester is designed specifically for use with solar cells because cells collapse under high current draw – which is what batteries want when they are charging up so that they can be ready to go ASAP! When drawing current from a solar cell, at the very beginning the voltage is very high, then it slowly drops down as more is drawn until the input voltage collapses completely. So you have to be very careful when drawing current – too little and you lose out on efficiency, too much and your power goes away completely.
There’s a ‘sweet spot’ right in the middle, where you can get the most power output, which is called the Max Power Point. And this point varies with how much sunlight you get – so it isn’t something you can pre-program in with a comparator or anything. Instead, the energy harvester has to wiggle the power draw forward and back to find the maximum point. For large-scale solar installations, you’d have a microcontroller do the math for you, and adjust throughout the day – it isn’t hard to do MPPT, it just takes measurement and computation. But in small and low-current situations, you can’t spend all your power budget on a microcontroller to manage your battery charger.
First up, almost no extra components are needed: just a stabilization capacitor plus a capacitor for the switched-cap boosting doubler. Note that there’s no inductor because it seems to use a switched-cap boosting method for approximately 2x voltage output – so you will need to spec a panel that, when the MPPT voltage is approximately doubled, you’ll have about 0.3V above the battery voltage. There’s some math in the datasheet to work this out but basically in the end, use a panel with an open-circuit voltage – Voc – that is about 0.7 times the battery voltage. So, e.g. if you’re using a Lipoly, with a VBat of 4.2V, use a 3V solar panel – which is very common and inexpensive. For NiMH cells, add up the total series voltage before multiplying by 0.7 for the Voc desired. To keep your battery from overcharging, either use a separate battery charger chip that will do the constant-current to voltage-limited charging, or use a low cost over-voltage protection (OVP) chip as recommended in the datasheet.
If you’d like to integrate the Nexperia NEH2000BY Energy Harvesting Power Management IC into your next solar-powered product, thank your lucky stars because DigiKey has the NEH2000BY in stock right now at a great price for immediate shipment. With the long summer days ahead, you can order today and be max-power-point’ing before the sun sets tomorrow.