TXB0106: Ground Shifting Issue

Arijeet Saha

Part Number: TXB0106
Other Parts Discussed in Thread: SN74AXC2T245

Hi Sir,
We are using TXB0106 as a Level Translator between 1.8V to 3.3V domain. When we are transmitting any signal(UART) in 1.8V to 3.3V direction, We are facing a ground shifting issue on the UART_RXD line(at 3.3V side) on connecting my sensor board(3.3V domain) to my controller board(1.8V domain). Are we missing in designing?
Please help with this.

over 4 years ago

0 Emrys Maier over 4 years ago

TI__Guru* 97046 points

Hello Arijeet, and welcome to the forums!

It's most likely that you have a pull-up resistor in your design, and the TXB logic family doesn't work well with pull-up resistors. This could be a weak pull-up inside one of the devices it is connected to. This of course is just a guess since you haven't shown my anything yet.

Can you share a schematic of your design and scope shot of the issue (preferably input and output together)?

0 Clemens Ladisch over 4 years ago

Guru 316690 points

What is that ground-shifting issue? You have not told us anything about it.

Do the boards conform to the restrictions in sections 8.3.4 and 8.3.6 of the datasheet? How long is the connection between the boards?

0 Arijeet Saha over 4 years ago in reply to Emrys Maier

Prodigy 160 points

Hi Emrys,

Thank you for the response.
Please find the schematics sections and scope shots.

Schematics-

Scope image-

0 Emrys Maier over 4 years ago in reply to Arijeet Saha

TI__Guru* 97046 points

Each output on the TXB0106 has a series 4kohm resistor. The most likely answer is that your SNSR_3V3 input has an internal pull-up resistor of value 6.3 kohm. The TXB family of translators is not compatible with pull-up or pull-down resistors.

If this can be internally disabled, then that would be the best solution. Otherwise you may have to go with a different translation solution.

0 Arijeet Saha over 4 years ago in reply to Emrys Maier

Prodigy 160 points

We are using this LT for the UART interface, and UART has internal PUs. Those can't be disabled. Is there is anything else we can do?

Thanks for the response

0 Emrys Maier over 4 years ago in reply to Arijeet Saha

TI__Guru* 97046 points

No, unfortunately TXB is not compatible with pull-up resistors due to its design.

For UART translation, I would instead recommend using a unidirectional voltage translator like the SN74AXC2T245. That type of device will be able to overdrive the internal pull-up resistors without any problems.

0 Arijeet Saha over 4 years ago in reply to Emrys Maier

Prodigy 160 points

Ok; thanks for the suggestion.

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TXB0106: Ground Shifting Issue