Logic level conversion

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welkin87

Joined Nov 18, 2010
32
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!
 

crutschow

Joined Mar 14, 2008
34,285
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.
 

RiJoRI

Joined Aug 15, 2007
536
... This Digital Logic Pocket Data Book[/URL] is a handy file to keep on hand.
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
 

crutschow

Joined Mar 14, 2008
34,285
Thanks for the help. Speed isn't much of an issue. I like the suggestions except for the packaging. I really need through-hole unless there's any suggestions on how to hook a surface mount device to a through-hole prototype board.

Would this thing work?
http://search.digikey.com/us/en/products/SN74AHC541N/296-4610-5-ND/376228
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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