Just a message to know if someone has ever tried 3.3v input signals on a 74HC595 chip (or more generaly a 74HCxxx) 5V powered.
On its datasheet, for a 4.5v Vcc the trigger is supposed to be at 3.15V so I was wondering if anyone in this forum has ever tried.
You can 't reliably drive a 74HC series device operating on a 5V Vcc with a 3.3V device without a level-translator of some type. It's common for manufacturers to spec the Vih level as 0.7 x Vcc. For a 5V Vcc this gives you a Vih of 3.5V.
What you need is a ' bi directional translator ' chip , if you search your local specialist supplier you should find some, Texas do a range - most seem to be smd, but are hand solderable with care if you get the Soic types.
Not a well considered suggestion, I think.
- No bidirectional level translation is required
- The usual solution is using 74HCT instead of 74HC devices. They can be driven from 3.3V logic. Alternatively 74HCT buffers can be used as level translators.
Actually I didn't chose the 74HC devices... they are a part of the constraints...
That's why I just want a simple solution to adapt 27x 3.3V > 5V signals