I have a circuit in which I interface a radio module running on 3.3V indirectly from a 5V supply.
I use a regulator to provide the 3.3V module VCC and the data is exchanged between both circuits through double-inverters (74HCT04).
This setup does work, but I read that if I used 74AHCT parts in place of 74HCT then the speed of operation will be 2-3x faster.
If I exchanged the 74HCT04 with a 74AHCT04, would the part still work or would there be special clamping diodes (like in the 74HC series) that would prevent the voltage conversion on the data signals to take place?
The data being exchanged between the radio module and the rest of the circuit is continuous and digital at the speed of 38400bps.
Best Answer
The 74HCT04 is plenty fast enough (~25ns) for 38.4k transmission speed (26usec/bit). 8ns vs. 25ns will not be noticable, though as analogsystemsrf points out, it may cause more ringing that may or may not be a problem.
The main difference you may notice is that the AHCT part draws about double the supply current when the inputs are at ~3.3V (~1.5mA per input at ~3.3V vs. ~0.75mA per input at ~3.3V).
Clamps do not come into play when the IC is powered from +5 (and it is not specified for 3.3V power). The HCT has diode clamping to Vcc.