32bit microcontrollers aim for system power reduction in the Internet of Things

32bit microcontrollers aim for system power reduction in the Internet of Things

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By eeNews Europe

The Precision32 SiM3L1xx MCUs integrate a 50MHz ARM Cortex-M3 processor core with mixed-signal blocks including an on-chip DC-DC converter. This helps reduce power consumption to 175 µA/MHz in active mode and less than 250 nA in sleep mode with the real-time clock (RTC) enabled at 3.6 V, but it is the ability to reduce the system power that is vital, says Mike Salas, vice president and general manager of the MCU business at Silicon Labs.
"Everyone talks about the headline power consumtion but the key is the focus on the system level power isues and specifically for this family on the use cases that allow us to optimise the system power," he said. The devices are aimed at smart metering, utility monitoring, home automation, wireless security, asset tracking, personal medical devices and other power-sensitive applications.
The integrated DC-DC converter is significantly more efficient than a low drop out (LDO) regulator and can control the power to external peripherals to optimise the current consumption and use the CPU to switch off the peripherals when not in use. Further system power reduction comes from adding additional state machines and DMA engines to handle packet creation and data movement without even waking the CPU core for wireless and sensor applications.
“Low-power design is especially challenging because developers must consider many different application-specific optimizations to meet their desired low-power targets,” said Salas.“The new Precision32 mixed-signal MCU family is unique in the industry because it provides an unprecedented combination of advanced peripherals, innovative architecture and power-aware design tools to give developers the flexibility to optimize their designs for the lowest system-level power.”
The new Precision32 mixed-signal MCUs include power-saving peripheral and architectural innovations that can reduce current consumption below that of many 8-bit MCUs, with active mode power reduction achieved through a number of key innovations. For example, dynamic voltage scaling adjusts the internal device voltage in response to changing conditions. The integrated, high-efficiency dc-dc buck converter reduces active mode power by 40 percent compared to competing 32-bit MCUs. Dedicated peripherals such as a data transfer manager, AES encryption block and run-time encoder accelerate the processing of RF protocol for wireless applications without CPU intervention, greatly reducing system power.
Enhanced direct memory access (DMA) can reduce protocol-related power by 90 percent, and RAM and register state retention enables a fast 4 microsecond wake-up time. The MCU family also features a patented LCD controller with a charge redistribution architecture that reduces the display’s power consumption by nearly 40 percent without compromising performance.
The SiM3L1xx MCUs also achieve significant reduction in sleep-mode power by optimizing on-chip peripherals (charge pump, RTC, sensor interface, sleep mode UART, comparator and LCD controller) for the lowest power consumption. The charge pump generates a power-efficient input voltage for the device circuits in sleep mode, which reduces analog sleep currents by 35 percent and digital sleep currents by 50 percent. SiM3L1xx MCUs support a multi-alarm RTC for clocking and interrupts, a sleep-mode UART for low-power device communication, and an integrated sensor interface that provides sensor stimulus and measurement while the MCU is in sleep mode. The autonomous sensor interface continues to count in sleep mode and can wake the MCU after a count overflow or when the count reaches a programmable threshold.
The SiM3L1xx and supporting development tools were designed with the overall system power budget in mind. To minimize system-level power, the SiM3L1xx MCUs feature patented voltage conversion technology, as well as advanced peripherals that reduce the power consumed by other ICs in the system. Configuring the output voltage to the lowest acceptable setting of the other IC components connected to the MCU minimizes overall power consumption. This technique is especially useful in battery-powered applications such as smart meters where this innovation can extend the battery’s lifetime to 20 years.
The Eclipse-based IDE and AppBuilder software include new, first-of-a kind capabilities for estimating power consumption and providing configuration guidance to achieve the lowest system power. Power Estimator provides a graphical representation of the total supply current and additive currents for enabled peripherals. The raw current values of each peripheral clearly show where power is being consumed, and a pie chart shows the percentage of each peripheral’s power usage relative to the total current. Power Estimator automatically updates the design with configuration changes, allowing designers to optimize each mode for the lowest power. Power Tips provides software configuration guidance that helps developers minimize current consumption. The feature automatically appears within AppBuilder when the cursor hovers over a configurable setting. Having the ability to see power optimization tips while configuring the MCU saves considerable development time.
AppBuilder software also makes the developer’s job easier by streamlining peripheral selection, initialization and pin-out customization for Precision32 MCUs.
Production quantities of Silicon Labs’ SiM3L1xx MCUs are available now in QFN and TQFP packages as small as 5.5 mm x 5.5 mm with 32 to 256 kB flash sizes. Product pricing for the SiM3L1xx MCUs in 10,000-unit quantities begins at $2.55. Comprehensive unified development kits include the SiM3L1XX-B-DK kit (without LCD) and the SiM3L1XXLCD-B-DK LCD kit, each priced at $99.

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