A set of peripherals tailored for low power

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A set of peripherals tailored for low power

Several peripherals require special attention, either because of their intrinsic high

consumption or because they are always powered up.

The STM32L0xx embeds a 12-bit / 1.14 MSps ADC. This very fast but accurate converter

can jeopardize the battery lifetime if left powered-up continuously, with a 300 µA typical

consumption at maximum speed. As the ADC consumption is roughly proportional to the

acquisition frequency, from consumption standpoint the application can choose between

two solutions, either performing the acquisition at low speed to limit maximum current or

doing it at maximum speed to switch in ultra-low power mode quickly.

When the acquisition is performed slowly, the ADC consumption itself can go down to few

tens of µA drastically limiting the maximum current. This can be mandatory when the power

source provides a limited current. The drawback, if the CPU has no other task to perform

during that time, can be the increased time spent in run or sleep mode (or Low Power run or

Low power sleep modes) versus the time spent in ultra-low power mode (stop or standby).

When the acquisition is made at high speed the ADC can go in low power mode thanks to

auto-off mode very quickly and the micro controller can go into ultra-low power mode as

soon as the acquisition is processed.

Seven peripherals have been developed to operate continuously even in Stop mode, where

the system clock is stopped, with the main oscillator and memory powered down.

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A pair of ultra-low power comparators is available to monitor analog voltages with a

current down to 3 µA. These comparators can wake up the MCU as soon as the

external voltage reaches the selected threshold and they can be combined together to

provide a window comparator. One of these comparators has a rail-to-rail input

capability and its output can be redirected to a timer for a general purpose use.

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An RTC peripheral provides a clock/calendar with two alarms, includes a periodic

wake-up unit and several application specific functions (timestamp, tamper detection

…). It can remain enabled in the lowest power mode (standby) where most of the chip

is powered down, and wake up the full MCU circuitry in case of an alarm or tamper

detection for instance. It also contains 80 bytes of backup registers to store contextual

information when exiting from standby mode. This peripheral has been designed using

asynchronous design techniques to minimize its consumption (below 1 µA).

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The glass LCD is one of the most common displays in low power applications, because

of its inherently low current consumption, low price and customization easiness. The

STM32L0xx includes a versatile LCD controller, which can drive displays with up to 8

common lines and 32 segments, with the capability of selecting individually the I/O

ports assigned to the LCD for an optimal use of the chip alternate functions. It also

controls an optional internal step-up converter to maintain the LCD contrast on a wide

included).

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The Low power timer (LPTIM) is a 16-bit timer that benefits from the ultimate

developments in power consumption reduction. Thanks to its diversity of clock sources,

the LPTIM is able to keep running whatever the selected power mode. Given its

capability to run even with no internal clock source, the LPTIM can be used as «Pulse

Counter» which can be useful in some applications. Also the LPTIM capability to wake

up the system from low power modes, makes it suitable to realize «Timeout functions»

with extremely low power consumption. The LPTIM introduces a flexible clock scheme