Logic level conversion

Discussion in 'General Electronics Chat' started by welkin87, Mar 14, 2012.

  1. welkin87

    Thread Starter Member

    Nov 18, 2010
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    I am using a DAQ that outputs TTL level logic (+5V) but the device I am driving can only accept up to 3.6V. I'm looking for some type of chip or device that will convert 10 channels of +5V (TTL) to +3.3V (LVTTL). Any suggestions?

    I would rather not use a simple voltage divider. I need something that can handle a varying load but maintain 3.3V. Also, I tried a TI SN74HC245 logic buffer a co-worker suggested but it didn't work.

    Thanks!
     
  2. crutschow

    Expert

    Mar 14, 2008
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    The HFC40109 4-bit buffer has separate input and output power pins that can be any voltage relative to each other. So it can be used as either a low to high or high to low converter, and requires no resistors.

    It operates at standard CD4000 speeds, however. What is the speed of your signals? If you need more speed the SN741VC425 is an 8-bit device or one of these should work.
     
  3. Ron H

    AAC Fanatic!

    Apr 14, 2005
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  4. RiJoRI

    Well-Known Member

    Aug 15, 2007
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    Obviously, TI has NOT printed this book! Or Marketing has gone crazy! An 800-page "pocket" book? My pockets are NOT deep enough! (But I downloaded a copy, anyway!)

    --Rich
     
  5. welkin87

    Thread Starter Member

    Nov 18, 2010
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  6. crutschow

    Expert

    Mar 14, 2008
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    That would work if you operated the device from 3.3V and added a resistor in series with each input to limit the input current since each input has clamp diodes going to Vcc and will start conducting current when the input is about 0.6V greater than Vcc.

    Alternately the HFC40109 I mentioned is available in a DIP package also.
     
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