FST3253 Mux Switch: Using 3.3V Serial Inputs with 5V Supply—Is It Safe?

The discussion addresses the compatibility of using 3.3V serial input signals with an FST3253 analog multiplexer switch powered at 5V. The FST3253 datasheet specifies a supply voltage (VCC) range of 4.0V to 5.5V and input/output voltage (VIN/VOUT) range of 0V to 5.5V. It is confirmed that serial inputs operating at 3.3V are acceptable as long as they remain within the ground to supply voltage range of the switch. The serial inputs share a common ground with the 5V supply powering the FST3253. A potential issue arises if the 3.3V inputs are active while the 5V supply to the switch is off, which could cause damage or malfunction. In this case, the 3.3V inputs remain permanently on, so care must be taken to ensure the 5V supply is also active when inputs are present.
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