TB5T1

Hi Anton,

The problem with having separate ground connections for each system is that there is an unspecified potential difference between the grounds.  This means that the line's common mode voltage (which is regulated by the transmitter with respect to its own local ground) may violate the receiver's specification (since these specifications are with respect to the receiver's gound).  The TB5T1 is capable of handling a wide input range (-1.1 V to 7.1 V), so if you know for certain that the maximum ground potential between the different nodes will not result in this specification being violated then the configuration you proposed should work.

One common method to ensure the differential signals' common mode voltage is within spec is to AC-couple the differential line and provide a different common mode bias point at the receiver.  If your application requires operation down to DC, though, AC coupling is not an option unless some sort of encoding or modulation scheme is introduced.

For operation down to DC, one method of solving this problem is to use isolators.  This allows you to forward a ground reference voltage to a remote receiver without having to connect the two grounds.  This allows for the transmitter and receiver to share a gound node without introducing a ground loop.

Here is an application note that discusses this issue in more detail:

http://www.ti.com/lit/an/slyt298/slyt298.pdf

See Figure 8 on page 14 for an example implementation.

Best regards,
Max Robertson
Analog Applications Engineer
Texas Instruments
m-robertson@ti.com