LSF0102: Logic Low level not zero

The LSF is a passive switch with a certain resistance. If you are using small pull-up resistors, the current through and the voltage drop over the switch becomes larger. (And the output voltage of the device that is actually driving the line becomes larger, too.)

Try to use larger pull-up resistors, if this is possible with the desired signal frequency. Alternatively, use a different translator; see [FAQ] Are there voltage level translation / level shifter device recommendations for the industry standard interfaces like GPIO, SPI, UART, I2C, MDIO, RGMII, I2S etc?

Hi George,

Clemens is correct. This is explained in detail in this video: https://training.ti.com/down-translation-lsf-family?context=1134826-1139264-1134793

These voltages imply that some other device sinks current. Is there anything else connected to these signal lines?

I do not know why that table mentions four-channel devices for UART. You could use the TXS0102 (which is like the LSF0102, but with edge accelerators, which allows it to use much larger pull-up resistors) or the TXB0102 (which has very weak output drivers and does not work well with pull-up/-downs).

I would have recommend a direction-controlled translator (with proper output buffers) for this, but there is no 5 V device that allows two channels in opposite directions. So for the 3.3 V to 5 V translation, I suggest a buffer with TTL-compatible input (e.g., SN74AHCT1G125), and for the 5 V to 3.3 V translation, a buffer running at 3.3 V with overvoltage-tolerant input (e.g., SN74AHC1G125).