I've been asked to check a design in which a micro-controller driving an AD7715 was replaced.
The old one was powered in 5V, so the AD7715 was too.
The new MCU is 3.3V powered, thus are the IO lines, but the AD7715 is still 5V powered..
The MCLK is fed by the MCU and it apparently works fine.
However the datasheet states that the threshold voltage for MCLK input is 3.5 V when DVDD=5V (unlike others which are 2.5V)
But it works!!!
So the question is: how stable this operating mode can be?
What is the behavior of the VIOH threshold with temperature or other environmental parameters?
In short, is it safe to leave it as is, or is it preferable to add a level shifter?