Convert 5V TTL Digital in to 3.3 volt for use with NI-6583 Flex RIO Module

[herrlin]

I am looking for some ideas on how to reliably convert a 5VTTL input signal only, operating at 2.5MHz, to 3.3v logic so that I may safely analyze it with a NI-6583 Module and NI PXIe7961R Flex RIO.  Any suggestions?

[Benjamin38]

Hi Herrlin, 

If you are looking to simply convert a 5VTTL signal down to a 3.3V logic level so that it can be used as an input for the FlexRIO 6583, you will need an external/conditioning device to do so.  You can find multiple versions of a Logic Level Converter such as this one seen here: http://www.sparkfun.com/products/8745 .  This one in particular is for converting 3.3V to 5V TLL and vise versa.  I have attached a schematic of the device below as well.    

[herrlin]

Ben

Thanks for the feedback.  My only concern with using a simple voltage divider is the that if my high logic level is at the low end of the spec for 5V will not be in spec for 3.3V after the divider.  Any thoughts?

Thanks

[Benjamin38]

Herlin, 

There are a number of ICs that could accomplish this conversion from vendors such as Texas Instruments, Analog Devices, etc.  The voltage divider circuit and schematic I provided in the last reply is one option.  If this voltage divider won't work for you application, I would look into a discussion forum that I came across here.  There are multiple users that have addressed the quandary that you are dealing with in the forum I linked and have multiple suggestions on ICs that they have used to make the appropriate conversions.  Hopefully this should give you some recommendations and a solid starting point for choosing the device that would best fit your application.