Optimizing power consumption— whether for consumer, industrial or medical applications—has typically been addressed by reducing active processing time and increasing how long processors can reside in sleep mode.
With the rise of ultralow-power applications, however, this approach no longer suffices. Trends such as single-cell operation, charging/discharging closer to battery thresholds, and the need to control motors and/or high brightness LEDs (all while reducing device form factor and cost) have changed how developers must approach power optimization.
For devices such as electric toothbrushes, personal media players, remote controllers, wireless sensors and a wide range of other portable and handheld devices, power management needs to be implemented at all levels of a system.
By optimizing power consumption through efficient single-cell voltage conversion, using multiple current modes, introducing smart battery management and implementing power saving techniques at the application level, power consumption can be coordinated across an entire system.
Achieving efficient conversion
Many ultralow-power applications are moving to single battery cell architecture to reduce device cost, size and weight, three of the key factors that determine the success of battery-powered portable applications.
Oftentimes, the battery is heavier than all of the other components and PCB combined. In addition, standard AA or AAA batteries are typically the single largest component on the PCB. Reducing the power supply to a single cell is attractive because it simplifies battery holder mechanics, and results in significantly smaller and lighter overall product construction.
Designing to a single-cell power supply, however, introduces a variety of new challenges for designers. While the voltage from a single battery cell usually ranges from 1.2V to 1.5V when fully charged, cells can drop below 1V while still possessing a substantial amount of usable energy.
Even MCUs with a 1.8V power supply require at least two cells in series to operate and some applications, such as driving high-intensity LEDs with high forward voltages, require as many as four cells.
To drive motors, LEDs and even the processor itself from a single-cell, a regulator is required to boost the available voltage to appropriate levels. Boost regulators, however, can cost on par with an MCU and require as much space on the PCB as well. Additionally, some regulators need to be controlled by an MCU, further complicating design.
The seamless operation of a self-managed integrated boost regulator within an MCU not only avoids most of the cost and space issues related to an external regulator, it can enable the MCU to provide greater draining efficiency than is possible using an external DC/DC converter.
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| Figure 1: Integrating a boost regulator enables the ATtiny43U to operate from a single cell with voltages as low as 0.7V, efficiently driving loads up to 10mA and allowing discharging to continue closer to the end of a cell's reserves compared to other types of implementations. |
For example, the integrated regulator of the ATtiny43U (Figure 1 above) is able to boost voltages as low as 0.7V, allowing discharging to continue closer to the end of a cell's reserves than is supported by other types of implementations.
An integrated regulator can also offer superior idle current -1 μA (typical) for the ATtiny43U - and automatically start as soon as there is sufficient voltage available (1.2V indicating a full battery is available or charging is near completion).
In addition, the regulator supports any battery technology, giving designers complete freedom in selecting the optimal battery for a particular application. Battery voltage can range between 0.7V and 1.8V, enabling developers to use 1.6V alkaline or silver oxide, 1.5V Li-ion, 1.4V zinc-air, and 1.2V NiMH and NiCd, among others.
