Ultra-safe supply monitoring

AN3193

10/13

DocID17369 Rev 2

6

Ultra-safe supply monitoring

The STM32L1xx includes a sophisticated supply supervisor module with several

programmable options. This module is active during both power-on/down and run-time

phases.

The power-up is a critical phase where the various parts of the internal circuitry must be

sequentially started and critical parameters (such as factory trimming values or options)

retrieved from the non-volatile memory to perform MCU initialization, even before the user's

from the battery insertion or because of a weak power source.

guaranteed operating conditions when the program execution starts.

Once the power-up phase is completed, the user can choose to activate or not the brown-

out reset (BOR) detector for a continuous battery monitoring, and select one of 5 thresholds.

This is an option stored in the non-volatile memory to make this power supervision

completely software independent. It is completed by a 7-level programmable voltage

detector (PVD) that can be enabled by software to generate an early interrupt in case of a

voltage drop.

The consumption of both the BOR and PVD modules is below 3 µA, when continuously

powered, but it can remain significant in the deep sleep modes. If needed, the power

supervision module can be programmed to have the BOR and the PVD disabled during the

deep sleep phase and enabled again automatically on wake-up events. This minimizes the

current consumption when the application is in idle mode (with usually a slightly higher and

very stable supply due to an extremely light load). However, this does not jeopardize the

safety when the execution starts again.

The STM32L1 is one of the few standard MCUs on the market with an operating range

down to 1.65 V and only very few limitations (USB, ADC and DAC cannot be used but all

other features are functional). A dedicated STM32L1xx device with permanently disabled

BOR is available and can be used in applications with a voltage tolerance of 1.8 V

8%.

In this case, a "zero current" Power-on / Power-down reset (POR/PDR) module remains

active and releases the reset after a hard-coded temporization. It is then up to the user to

when the reset vector is fetched.