I have a project where I want to interface with a keyboard matrix / scanner (this is a PCB from a consumer electronics device). There’s already an implementation that uses some analog muxes for this, but I’d like to change this to an MT8809 8×8 crosspoint switch: https://www.microsemi.com/product-directory/analog-cross-point-switches/4916-mt8809
That is, the MT8809 will be used to connect/disconnect the rows and columns of the matrix scanner to simulate keypresses.
The MT8809 runs at 4.5-12v, so I’d connect it to a 5v rail, but the device I’m interfacing to runs at about 3v. Are there any concerns here? Do I need to clip the voltage?
You can connect 3V signals to inputs of 5V devices and it should work. But you can't input more than 3V into a 3V powered device even if the said device can run on more than 3V. As a general rule (except if otherwise explicitly mentioned in the datasheet) input voltages should never exceed the supply voltage of the device.
In the case you have a 5V signal which should be used as input into a 3V powered ic, use a resistor and a 3V zener diode to limit the voltage, or two resistors to create a voltage divider.
Answered by Fredled on November 16, 2020
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