TXS0108E: Only one direction works in TXS0108E

Cheng Shen

Part Number: TXS0108E

Dear sir and madam.
In my design, I use TXS0108E to transfer the 1.8V Data Bus to 3.3 DataBus.
A side of TXS0108 is connected to 1.8V FPGA GPIO. And B side of TXS0108 is connected to 3.3V MRAM Data Bus.
The FPGA is XC7VX690T-2FFG1927. The MRAM is MR4A08BCYS35.
We meet the following problem.
Now we can write data from FPGA to the MRAM, but we can not read the data in MRAM.
By using a oscilloscope，We found out that the A side changes will result in the changes of B side. However,When the B side changes from 0 to 1, the A side always stay in zero.
We do not use the pull up resistor.

over 3 years ago

0 Emrys Maier over 3 years ago

TI__Guru* 96591 points

Hi Cheng, and welcome to the forums!

Can you please post a scope shot showing the input and output for the channel that's affected?

0 Clemens Ladisch over 3 years ago

Guru 244220 points

Please note that the TXS has internal pull-up resistors; an I/O can be low only when an external device actively drives the line low.

TXS switches have a resistance of about 300 Ω; by comparing the voltages at the A/B pins, you can determine in which direction the current flows, i.e., which device drives low.

Can you confirm that the FPGA pins are configured as inputs?

0 Cheng Shen over 3 years ago in reply to Emrys Maier

Prodigy 20 points

thank you very much！
we found that there are some bugs in our fpga program. The circuit works very well.

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TXS0108E: Only one direction works in TXS0108E