TXS0108E: Issue with UART communication through level translator

Taylor Sullivan-Peters

Part Number: TXS0108E
Other Parts Discussed in Thread: 2N7001T, TXU0202

Tool/software:

Hi there,

I'm struggling to get a UART port to an FTDI cable TTL-232R-3V3 up and running on a carrier board for an Ezurio SOM and I wonder if the issue isn't my level translator -- need to go up from 1.8V to 3.3V.

We borrowed the level translator part from the carrier board the manufacturer uses, but the manufacturer also has an RS232 driver after the level translator. We're trying to go straight from the level translator into an FTDI cable with no luck.

Is it possible this bi-directional part isn't appropriate for my implementation and I ought to explore unidirectional alternates like the 2N7001T?

9 months ago

0 Clemens Ladisch 9 months ago

Guru 318700 points

In theory, this should work. Please show the schematic.

But a UART has only two signals. Why aren't you using the TXU0202?

0 Taylor Sullivan-Peters 9 months ago in reply to Clemens Ladisch

Prodigy 60 points

I have multiple UARTs are I am trying to translate, one of which I wanted to put provisions for flow control in, which is why I'm using such a large level translator.

For what it's worth, I put a uni-directional buffer after the level translator on the TX output line and got it working, so something about the level translator was making my FTDI cable unhappy.

0 Clemens Ladisch 9 months ago in reply to Taylor Sullivan-Peters

Guru 318700 points

This schematic does not show what is connected to the I/Os. If the buffer helps, then I suspect that there is some load that is too high for the device on the other end.

0 Taylor Sullivan-Peters 9 months ago in reply to Clemens Ladisch

Prodigy 60 points

To be clear, the UART I'm having issues with is the one that goes to J11 in the schematic. That goes off-board to a TTL-232R-3V3 like I mentioned above. I believe you are right that somehow the level translator does not have the drive strength to handle whatever is in the front end of that cable. For the time being I've built up a dongle that converts the output of this translator to RS232 and in a future revision I will likely design this part out.

0 Clemens Ladisch 9 months ago in reply to Taylor Sullivan-Peters

Guru 318700 points

The TXS is a passive switch and does not have any drive strength. The device connected to U34L must drive everything.

+1 Jack Guan 9 months ago in reply to Clemens Ladisch

TI__Mastermind 44691 points

Hey Taylor,

Since your have 8 signals requiring translation from 1.8V<-> 3.3V (4 from A-> B, and 4 from B->A), then a direction controlled translator works here. For instance, the AXC8T245 can be used here with DIR1 controlling first bank of 4 signals in one direction, and DIR2 controlling the second bank of 4 signals.

Regards,

Jack

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TXS0108E: Issue with UART communication through level translator