SN74AXC4T774: Applying 3.3V control okay?

Go Bravos

Part Number: SN74AXC4T774

We have this as a logic translator from 1.8V to 2.5V. We have a 10k pull up from the OE to the 1.8V (on the VCCA line) as per the data sheet. We are using 3.3V logic to drive the OE. It appears that this is not an issue but wanted to confirm that applying a +3.3V control or OE on this part when VCCA is +1.8V and VCCB is +2.5v.

over 4 years ago

0 Emrys Maier over 4 years ago

TI__Guru* 97046 points

Hello,

Yes, I can confirm that you are correct. This falls within the recommended operating conditions for the device:

0 Go Bravos over 4 years ago in reply to Emrys Maier

TI__Expert 6090 points

The main concern is that VCCA will be at 1.8V but OE will be at +3.3V so wanted to make sure that since there was no Max OE voltage when VCCA is at 1.8V. I wanted to make sure the part then did not try to bias or power through the OE pin if that voltage or logic is higher than VCCA.

0 Emrys Maier over 4 years ago in reply to Go Bravos

TI__Guru* 97046 points

Yes, I understand. This is a valid concern and something you should check through the datasheet before doing it.

This is probably the most frequently asked question on the Logic forum -- we have an FAQ that covers in more details here:

[FAQ] Can the input voltage (Vi) to my logic device be higher than the supply voltage (Vcc)?

0 Clemens Ladisch over 4 years ago

Guru 316510 points

Please note that a current will flow through the 10 kΩ resistor into the 1.8 V supply. If the supply cannot sink that current, its voltage is likely to rise above 1.8 V.