MCU halves battery demands

25 February 2008

Integration has led to a microcontroller that enables devices to be powered from a single cell battery

Nuremberg, at Embedded World: By integrating a D/C/DC boost converter into the 8bit architecture of the C8051F9xx family, Silicon Laboratories believes it has produced an MCU that can halve battery requirements for both portable consumer products and medical equipment.

The company is already beta-testing the devices in personal medical devices as well as in remote meter reading. The devices operate in dual or single mode and is targeted at reducing the batteries required in low-power applications and to introduce applications currently restricted because of battery budgets.

By supplying up to 65mW for internal MCU use and to drive other components, the five devices can create a true, single cell battery system, powering user-replaceable batteries in wireless computer mice and other computer peripherals, portable medical devices, such as blood pressure monitors, remote controls and portable audio devices.

The MCUs operate down to 0.9V and up to 3.6V, from a single cell battery and has been optimised for fast wake-up, low power during active mode and an efficient sleep mode, to reduce the power consumption and drain. The proprietary design removes the traditional second cell, the LDO. In this traditional solution the integrated LDO requires a constant current and constant voltage. When the voltage changes, so does the current which means a strong dependence and a high operating current, lowering the efficient of the device.

Silicon Laboratories uses a 0.18um CMOS process instead of the conventional 2.5um or 3.5um because this has a lower leakage. The lower geometry exhibits a lower active mode, hence less leakage. Building on this efficiency, the Austin-based company has organised the device so that it is in sleep mode for most of the time in low-power applications, waking to capture data. The only block in the circuit that is on in any mode, i.e sleep, wake-up modes, is the power management unit. By turning off all the 0.18um transistors, the device can maintain the digital state for a quick wake up and execution of an operation. Active-mode current can be down to 170uA/MHz. Typical sleep mode current is less than 50nA.

The company’s SmaRT Clock oscillator preserves a function for 36 hours to avoid having to wake up, reset and returning to sleep mode, reducing the power consumption.

There is also up to 64kByte flash memory and 4kByte RAM. This provides extra memory for operations such as data logging, if required. RAM is also used to retain a wait state down to 2.9V for the low power sleep mode current and fast wake up of 2usec to 25MHz operation. Settling time is 1.7usec, compared to 17msec for competitive devices, claims the company.





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