Proneness to low/high power supplies

[dmohns]

How does the device behave if a user (or potentially malicious actor) supplies extremely low or extremely high voltages?

[knakwaboah]

Need to look at the register settings but based on the datasheet for the Atmel M90E26(Section 2.3.2),the chip has a voltage sag detection property that can detect low voltage. Voltage sag is detected when voltage is continuously below the voltage
sag threshold for one cycle which starts from any zero-crossing point. The voltage sag threshold is set in the M90E26 register. If not enabled, the voltage sag will be disable during power on.
When the supply to the meter is below the defined threshold, the m90e26 will set the SagWarn bit and this will cause the IRQ that connects the main microcontroller (STMxx) and M90E26 to be high. This can tell the microntroller that something has happened in the meter and needs to be checked. It can also be used to call other functions like turning the relay off and cutting supply to the customer.

The IRQ pin outputs high level when there is any metering / measurement parameter error, active/ reactive energy direction change, voltage sag, metering line change in anti-tampering mode, etc.

The SMPS has a switching IC (UC3843) that can handle the undervoltage and overvoltage but I will need to check the datasheet to see the performance
uc2845a.pdf