5v analog switch for 3.3v logic ok?

Electrical Engineering Asked by BobIsNotMyName on November 16, 2020

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:

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?

One Answer

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

Add your own answers!

Ask a Question

Get help from others!

© 2024 All rights reserved. Sites we Love: PCI Database, UKBizDB, Menu Kuliner, Sharing RPP