Electronic Design

DC-DC Converter Makes Single-Cell Microcontroller

Silicon Labs has met the challenge of cutting power consumption to a single cell with its C8051F9xx, which fits into a 4- by 4-mm package (Fig. 1). Ranging from 0.9 to 3.6 V, its operating voltage is ideal for one- or twocell solutions.

This 25 MIPS, 8051-compatible microcontroller has a 5-V tolerant I/O with a built-in 24.5-MHz (2% accuracy) clock. It also boasts a second, low-power 20-MHz clock and a 32-bit SmaRTClock timer in addition to multiple 16-bit timers with pulse-width modulation (PWM) support.

The key is a dc-dc converter and low-dropout (LDO) voltage regulator that was designed specifically for the chip, allowing it to operate with efficiency between 75% and 90%. It supplies a constant 1.7 V to the core, and it can even deliver up to 65 mW to the chip and external devices. In sleep mode, the chip draws less than 50 nA.

Typical off-chip dc-dc converters cannot match this performance and efficiency across the range of voltages and current requirements. They usually provide more flexibility in output voltages as well as other features. However, they aren’t as relevant to a single-chip solution such as the C8051F9xx. For example, higher current would be overkill. Likewise, the C8051F9xx is an extremely tiny single-chip solution.

Silicon Labs’ tests show the C8051F9xx running twice as long as the competition in two-cell trials. Likewise, the chip can work with a range of battery technologies, from nickel metal hydride (NiMH) to zinc air in addition to traditional alkaline and lithium-ion (Li-ion) batteries.

The chip’s low-voltage operation provides other power advantages. For instance, a single AA has more power than a pair of AAA batteries, but it takes up about the same space. Similarly, migrating from a single AAA to a single AA increases battery life by 2.2 times. A power simulation application enables designers to estimate requirements early in a design (Fig. 2).

Silicon Labs didn’t skimp on the peripherals and memory. The chips have 64 kbytes of flash and 4352 bytes of RAM. A pair of comparators can handle up to 15 capacitive touch inputs and a 10-bit, 15-channel, burst-mode, 300-ksample/s analog-to-digital converter (ADC) with an internal voltage reference, allowing extremely fast wakeup/ record times from sleep mode. Digital peripherals include a UART, an SMBus interface, and a pair of master/slave serial peripheral interface (SPI) ports.

Pricing starts at $1.99. A $99 development board and low-cost ToolStick daughter cards that start at $18 are available (see “Silicon Labs Does It Again With New ToolStick” at www.electronicdesign.com, ED Online 14025).

SILICON LABSwww.silabs.com

See associated figure

Put Some Sunshine In Your Gas Tank

Sandia National Laboratories is building a prototype that will use concentrated solar power to chemically “reenergize” carbon dioxide into carbon monoxide, which then could be used to make hydrogen or serve as a building block for synthesizing liquid combustible fuel like methanol or even gasoline and diesel. Known as the Counter Rotating Ring Reactor Recuperator (CR5), the device should be complete by early next year. Tests breaking water down into hydrogen and oxygen are already under way, and researchers expect commercialization in 15 to 20 years. See associated figure

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