Can I pull down a 5 volt logic with this buffer?

Thread Starter

thatsmessedup

Joined Feb 15, 2018
59
Hello! I would like to find out if this is the correct way to accomplish my goal. I have a 3.3v microcontroller and I am attempting to use it to pull down a 5 volt logic for a power supply enable\inhibit pin (it is usually pulled up internally inside the power supply, thus its default state is enabled). I figured I could use a buffer\driver with an open-drain output to accomplish the pull down but I am not sure if this will be a problem or is the best solution. Does anyone have advice? Thank you very much.line.jpg
 

ScottWang

Joined Aug 23, 2012
7,295
The output of 07 is an open-drain and as you have mentioned that the enable\inhibit pin has an internal pull high, and the input/out has some kind of isolation, so it should be ok.
 

DickCappels

Joined Aug 21, 2008
9,297
Check the datasheet for the buffer and if there is any doubt about the isolation from the open drain output to the power supply, you can go with the NPN transistor solution. Just remember the base resistor, which would not be need with a very low threshold voltage MOSFET.
 

Thread Starter

thatsmessedup

Joined Feb 15, 2018
59
Check the datasheet for the buffer and if there is any doubt about the isolation from the open drain output to the power supply, you can go with the NPN transistor solution. Just remember the base resistor, which would not be need with a very low threshold voltage MOSFET.
Thank you.
The datasheet mentions these features:

• Wide operating voltage range. – Operates from 1.65 V to 5.5 V.
• Allows down voltage translation.
• Inputs and outputs accept voltages to 5.5 V.
• Ioff feature allows voltages on the inputs and outputs, when VCC is 0 V.

and I was not sure what down voltage translation meant so I was a bit hesitant.

Also it states "The inputs are 5.5 V tolerant allowing it to translate up/down to VCC." and my VCC is only 3.3v so I didn't know if that was a problem.
 
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