Driving 3.3V parts from 5V controller

[janneman]

Hi,

Not audio, but 'electronics and everything else', here goes.

I am designing a piece of audio equipment that involves a uController, an LCD and an analog level chip. The LCD needs 5V digital signals, the level chip can only work with 3.3V digital commands. The uC can run on either voltage.

I had this plan: run the uC and LCD from 5V, the level chip from 3.3V. Then drive the level chip control lines from the 5V uC via a resistor. The voltage at the level chip would rise above 3.3V, the internal protection diodes would limit that voltage to 3.3V + 0.5V, and the series resistor limits the current into the protection diodes to < 1mA.

Would that work? Or do I need to get some level translators?

Jan Didden

[paulb]

It sounds ok to me. I've done the same except I used external diodes, not relying on the internal ones. You could of course use zener(s) to be safer.

[janneman]

Originally posted by paulb
It sounds ok to me. I've done the same except I used external diodes, not relying on the internal ones. You could of course use zener(s) to be safer.

Hi Paul,

Thanks. Did you have an issue with a logical zero from the uC not being able to pull down the input of the other device because of the series R (I intend to use 1.8k)?

Jan Didden