I'm designing two MCU boards. These boards will be used for somewhat different purposes, but they should communicate with each other via UART. One of the MCUs has an I/O voltage of 5V, while the other has an I/O voltage of 3.3V. Thus I decided to use the push-pull logic level translator, TXB0104.

TXB0104 has 4-channels. I will use two channels for the UART lines and others for some simple GPIO lines. I'm going to mount the logic level translator on the 5V-compatible MCU board.

The problem is that I must protect all connectors from the ESD event. Of course, the connector for the UART lines should be also protected. The 5V MCU board should have its own protection circuit, and this is the same for the 3.3V MCU. Then is it okay that I put series resistors and TVS diodes to the UART lines in both of the boards? The datasheet of TXB0104 says that the IC can derive capacitive loads of up to 70pF. Can one use the circuit below without disturbing the operation of the TXB0104? series resistors and TVs diodes for ESD protection

The line should have a series resistance of 400 ohms, and the length of the wires is about 30cm. I'm thinking of using NSP4201 for the TVS diodes. The configuration of the diode array is different from the schematic diagram above, but I thought it would not make difference.

Also, I wonder how people protect such logic level translator IC from ESD event.

  • \$\begingroup\$ TI (among others) has a nice line in level translators: ti.com/logic-circuit/voltage-level-translation/overview.html \$\endgroup\$ Oct 16, 2018 at 11:07
  • \$\begingroup\$ @PeterSmith Isn't the TXB0104 one of those? \$\endgroup\$
    – Nownuri
    Oct 16, 2018 at 14:48
  • \$\begingroup\$ Why not use a voltage divider TX 5 -> RX 3.3 and mosfet/transistor TX3.3 -> RX 5? \$\endgroup\$
    – RemyHx
    Dec 2, 2022 at 5:16
  • \$\begingroup\$ Why do you need bi-directional? UART Tx is always an output, Rx is always an input, signal direction in each channel is one way, always Tx-->Rx. \$\endgroup\$ Aug 7, 2023 at 8:25

1 Answer 1


Better to use a couple of ICs. 74HC4050 powered by 3.3V for 5V to 3.3V, 74AC125 powered by 5V for 3.3V to 5V.

TXB010x are not designed for long wire runs, altho 30cm is not that long.

Run the signal and Gnd wire inside a shielded cable, with the shield grounded at one end. Where does the 400 ohm come from?

  • 1
    \$\begingroup\$ Are the 74 ICs bi-directional? The 400 ohms come from the series resistors. \$\endgroup\$
    – Nownuri
    Oct 15, 2018 at 19:20
  • \$\begingroup\$ Is UART use bidirectional lines? \$\endgroup\$
    – user263983
    Dec 4, 2020 at 1:10
  • 1
    \$\begingroup\$ UARTs do not typically use bidirectional lines. MCU1 Tx goes to MCU2 Rx, MCU1 Rx comes from MCU2 Tx. \$\endgroup\$
    – CrossRoads
    Jan 13, 2021 at 17:44

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