# Logic level shifting from 5v to 2.8v and vice versa

I need to use a logic level shifter in my circuit which translates 2.8V logic level into 5V and the other way round. I found this document. The device itself is presented on the page 10. It is very simple and consists of one mosfet and 2 pull-up resistors. However there is one catch. To use this device I need to have both 5V and 2.8V power supplies in my circuit. I only have a stable 5V line.

What would be the easiest way to solve this issue? I thought I could connect 3 diodes in series, which would drop the voltage about 3*0.65V = 1.95V, so I would have 3.05V left, which is a bit too high, but I guess it would work. But maybe there are easier ways to shift logic levels?

Try using 2.8V MCP702 lineer voltage regulator or you can select different 2.8V 3 pin voltage regulators from digikey.com. By the way select a regulator according to your current needs.

• With only 2uA Iq and 2.8V available as standard, this approach is probably your best solution. Commented Dec 17, 2014 at 19:47

You would use your 5V as input to an adjustable voltage regulator like the LM317: https://www.fairchildsemi.com/datasheets/LM/LM317.pdf

• Oh, I forgot too add that it is supposed to be a low power device. I probably can't afford an additional voltage regulator. Commented Dec 17, 2014 at 18:07
• Then you would use a switching regulator instead of a linear regulator, as they're more efficient. Dropping voltage across three diodes certainly isn't efficient. Commented Dec 17, 2014 at 18:45

Use a simple voltage divider network, select appropriate value of the resistors to get 2.8V from 5V and then add a simple voltage buffer circuit at the output of the voltage divider network to properly match the impedance of the network connected at the output terminal.

OR

An even better solution is to use a zener diode having reverse voltage of 2.8V. Just like this one: http://uk.farnell.com/micro-commercial-components/1n5224b-tp/zener-diode-500mw-2-8v-do-35/dp/1924531