Interfacing a LM1881 5V with a dsPIC 3.3V

Discussion in 'General Electronics Chat' started by tom66, Jul 11, 2010.

  1. tom66

    Thread Starter Senior Member

    May 9, 2009
    2,613
    213
    I need a unidirectional way to connect a LM1881 sync separator operating at 5V to a dsPIC operating at 3.3V, so I need to translate the 5V signal down to 3.3V.

    I could use a voltage divider but I was thinking, could I just take advantage of the internal diodes that the dsPIC has to clamp the 5V to 3.3V through current limiting resistors? I am trying to build this on a small stripboard so size is a driving factor.

    I don't want to blow up my dsPIC because they are £4 each and I only have two of them.
     
  2. tom66

    Thread Starter Senior Member

    May 9, 2009
    2,613
    213
    I figured out that the dsPIC has 5V tolerant IOs so I am going to be using all of those for my project. These will also be used to communicate between modules. The 5V IOs can accept up to 5.6V input... which is good for me.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Make certain to use resistors as connecting links. 170 Ohms would give you a 10mA current flow through the ESD diodes, which is about their maximum rating. I suggest that you use 510 Ohms or greater. 1k would give you 1.7mA current, and 1k resistors are as common as fleas.
     
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