+5 volt logic to 3.3 devices?

Discussion in 'General Electronics Chat' started by ssutton, Mar 20, 2013.

  1. ssutton

    Thread Starter New Member

    Sep 12, 2011
    I have a circuit that is using a PIC18f452 micro operating at 5 volts. I need to be able to communicate with a MAX31855 via SPI. My micro (because of other devices needs) operates on 5 volts but the MAX31855 at 3.3. What is the workaround for talking to devices operating at lower voltages? Will the MAX31855 blow up it I connect the comm pins directly to 5 volt logic and power it from 3.3?

    Thanks for your thoughts,

  2. WBahn


    Mar 31, 2012
    Look at the data sheet for the part you want to use and see if it's inputs are 5V tolerant.
  3. majd-ghadab


    Dec 25, 2012
    Hello ssutton
    you can use zener diode a value of 3.3v
    in picture uses 3.6 but you try to use a value of 3.3 and don't forgot to put resistor
    connections :
    MICRO out >>>> resistor and zener to ground >>>> MAX31855 input pin
    and if the max ic pin is output and micro pin is only input you don't have to worry
    cause 3.3V as i know is enough to be 1 logic
    and if its not you should use a transistor to boost the voltage form max ic output to micro input
    so there are many connections and its depending on the pins type
    warning :
    you must calculate zener resistor value by your self and it might be a good idea if you simulate it on a program like multisim or protues ....
    you don't have to use microcontroller in simulation and either max ic just any type of ic's that have the same type of pins
    another way is to use ic that converts 3.3v to 5 or 5 to 3.3
    Last edited: Mar 21, 2013