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I have a design where the enable pin of this part is connected to ground (always enabled) and Vcc = 3.3V. The output is pulled up with a 5.6k resistor to 5V.
I see 3.3V on the output pin, even with the pullup.
Possible explanations:
The 3.3 V power supply is sinking current through a body diode in the part
If there's no body diode involved, the part's output can't sink current and the output is at logic 1.
Questions:
Am I on the right track with the current-sink ideas?
We're seeing a lot of noise on the 3.3V at the ouput, enough to dip into the logic '0' range for 3.3V logic. Is this arrangement especially susceptible to noise?
Thanks,
Jeff
Hi Jeff
The pullup resistor supplies about 1ma of pullup current while the part is driving the output to 3.3 V with 24ma of available current. The only time the output could go to 5V is if the part is disabled or off.
Although not Ideal here is an option. Use 2 - LVC16T245 devices that can translate from 3.3V to 5V. http://focus.ti.com/lit/ds/symlink/sn74lvc16t245.pdf thes come in many bit widths but not 32.