Advantages over traditional power monitoring

AN1336

3

Advantages over traditional power monitoring

Typical power monitoring (or supervisory) devices offer features such as brown-out detect

below a minimum level. Some may also include chip-enable gating or chip-enable write

protection which will disable access to the memory, thereby protecting the SRAM contents

from errant writes by an MCU that is operating in an undervoltage condition. These are

good features and necessary to avoid catastrophic data loss, but unfortunately do not occur

early enough to allow the MCU to gracefully enter a fail-safe state. Any of the following

scenarios will result in unsatisfactory system shutdown:

Loss of processor state

When the RESET occurs, any information not already stored to the NVRAM will be lost.

This includes the processor state, the program status, and any information still in the

scratch pad RAM, but not in the NVRAM.

RESET occurs during a write cycle

If the MCU is writing to memory when RESET occurs, that data will most likely be

corrupted. This applies to EEPROM and Flash memories as well as NVRAM.

Write protect occurs before RESET

If the NVRAM gates off access to the SRAM prior to processor RESET, the processor may

continue accessing/writing the NVRAM expecting that the data written is secure (when it

has in fact, been lost).

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