Low-power MCUs for USB-connected IoT devices

May 18, 2015 OpenSystems Media

For me (and I’m sure many others) the terms “IoT” and “wireless” are synonymous – so I first reacted with surprise when Alf Petter Syvertsen (Product Manager of 32-bit Microcontroller Products) introduced Silicon Labs’ latest offering to the IoT space. Alf’s confidence that “Wired connectivity is not going away, there are still many legacy applications that need USB, despite the proliferation of wireless technology in so many areas these days” quickly quashed my initially skeptical perception of its value in today’s wireless world.

The reality is that IoT applications across smart energy monitoring, access, and environmental control, even the latest fad – wearable biometric devices – all still scream for USB connectivity, in fact more than three billion USB-enabled devices still ship each year. That’s where the Happy Gecko comes in, the latest addition to Silicon Labs‘ EFM32® 32-bit MCU portfolio and promising the smallest USB power drain in the industry – translating to protracted battery life and opening doors for new energy harvesting applications.

Prior to the Happy Gecko, IoT developers found including USB interfaces in mobile devices can double the application current consumption. Based on the ARM Cortex-M0+ core and utilizing cutting-edge 5 stage power minimization modes, the Happy Gecko’s raison d’être is to spend as little time as possible in true active mode. It achieves this via a six channel Peripheral Reflex System (PRS), which in layman’s terms enables peripherals to communicate autonomously between one another, without requiring CPU involvement. The PRS filters very specific events, only waking the CPU when it is absolutely required. Combined with an incredible 2 microsecond wakeup time from standby mode (industry standard is typically 5-14 µA), an industry leading current consumption of 0.9 µA in deep sleep and 130 µA/MHz at 24 MHz in active mode are achieved with ease.

In keeping with current trends, where developers continue to demand reduction in bill of material (BOM) costs and, in correlation, component count – the Happy Gecko’s family provides true single-die integration. Alternatives to derive USB functionality invariably require a plethora of external components and crystals, the Happy Gecko removing this need with a crystal-less architecture and on-chip regulation. All contained within a tiny 9 mm2 package, with a full, self-contained USB stack.

Another embedded industry trend is of course ease and expediting speed of development. Silicon Labs’ acclaimed Simplicity Studio development platform achieves just that and fully supports the new Happy Gecko platform – in fact supporting immediate migration of existing EFM32 MCU code to the new platform.

A key component of the Simplicity Studio, the Simplicity Energy Profiler permits real time monitoring of energy efficiency via profiling and live debugging of code – of course not purely for error identification, where one is looking to achieve the very minimum power consumption interrogating code to determine it is the most power efficient is just as important. An equally useful tool, the Simplicity Battery Estimator gauges anticipated battery life based on various configurations – also with the ability to consider external peripherals within the overall device.

Paying homage to the trend of development platforms, here ironically costing less than most USB devices themselves – the Happy Gecko starter kit is available now priced at $29 (USD MSRP).

Rory Dear, European Editor/Technical Contributor
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