On my board comes a UART line with a voltage of 3.3V. To safely communicate with the controller on 5V, I use a level offset based on BSS138 transistors. My goal is reliable ESD protection of the UART line from the 3.3V side.
For this, I want to connect RX_L and TX_L to ground using TVS diodes of low capacitance. The problem arose in the choice between unidirectional and bidirectional diodes. Doubts arose because I learned that the ESD voltage can be of different polarity, in some case a bipolar TVS could miss a pulse of reverse polarity and cause damage to the device. Tell me, is that so? What type is used for UART lines?