How is Atmos Tackling Power Management?
Proper power management is critical in all types of aircraft, from experimental to commercial. For the General Aviation (GA) world the main focus is to build for 12 to 28 volts DC. Even with that general voltage range (based on standard battery and alternator/generator output voltages) there are still concerns with that voltage range swinging from, lets say, 9 to 32 volts DC. Lets also add that GA aircrafts are starting to experience deteriorating electrical systems, due to their age creating electrically noisy environments as well. Then, with GA airplanes we also have to consider the limited available space in that we have to fit electrical equipment where we can. This means heat dissipation for avionics equipment is not always optimal. After we’ve considered all those critical aspects of our power supply design, we want to make it re-usable across the Atmos family of products.
There are a whole range of options that could have gotten us to our end result. We ended up deciding on the MPM3530GRF (MPM3530) from Monolithic Power Systems (MPS). MPS describes the MPM3530 as “...an easy-to-use, fully integrated, 55V input, 3A, step-down, DC/DC power module.” The MPM3530GRF is rated for input voltages from 4.5 volts to 55 volts DC. By using this option, we are exceeding our range of 9 to 32 volts DC by at least 40% on the high and low end.
The first thing that drew our attention in that datasheet was the following two statements: “The MPM3530 integrates a monolithic DC/DC converter, power inductor, input capacitors, and the necessary resistors and capacitors “ and “ …provides over-current protection (OCP)...accurate and reliable overvoltage protection (OVP) and auto-recovery thermal protection.” This helps reduce our overall BOM cost, board space, and design time. It also gives us room to include more external components to help ensure external noise does not interfere with our internal power supply.
With Draco (engine monitor) being the first offering in the Atmos family, we knew we would have to anticipate the enclosure experiencing high ambient temperatures because of limited and preferred mounting locations. The MPM3530 accounts for this by offering great passive cooling when incorporating MPS’s recommended copper layout guidance. Assuming a worse case scenario power loss of 2.25 watts, we would see a junction temperature rise of approximately 38℃. Let's assume another worse case scenario of an ambient temperature inside the enclosure of 60℃. That means our total junction temperature would be approximately 98℃. That puts us about 20% below the maximum suggested operating junction temperature of 125℃.
As Dalton mentioned in the previous blog, we are pursuing reusability across the Atmos family of products. This will help us keep the build cost down on our products for our end users. This will also help us expedite time to market for products on the Atmos road map. We want Draco to be the beginning of something new in the GA market. Our design approach and drive to integrate new technology will bring new options to the market which, in turn, satisfies a demand that our clients have been asking for for years. That is the goal and promise of the Atmos brand and that is what we strive to support: our clients.
-Auto Co-Founder/Hardware Engineer
