OK to put in 5V TTL into a LVTTL devices

[rnelsoneeJHU]

Hi all,

I'm using an NI 9402 (spec PDF here) in a cRIO which says it has LVTTL input (low voltage TTL, seems like 'high' is 3.3V) but maximum input voltage is 5.5V. Would it hurt to use a 'standard' TTL - customer says they have TTL on a BNC, which I think means 0.8V is low, and 5V is high. Maybe my issue is the 9402 says 0.8V is the maximum 'low'.

If not, I'd imagine I can just use a voltage divider or a COTS part?

Thanks! I'm more of a digital weenie - I just don't want to break this nice card 🙂

- Rick

[crossrulz · Accepted solution]

The spec actually says a maximum input voltage of 5.25V.

This is somewhat common with bidirectional DIO anymore that the input can accept TTL levels, but the output will be LVTTL levels.  Since the thresholds are the same, there is no issue, assuming little to no current draw.

[rnelsoneeJHU]

Thank you! Yeah, I was figuring LVTTL was an output spec vs an input and output spec. I will move foward with the design then.