TXB0104: TXB0104 application question

Dane Zhang

Part Number: TXB0104
Other Parts Discussed in Thread: SN74AXC4T245

Hi team,

The Level Shift chip is used as a switch function. It is enabled by controlling EN to cut off or connect to UART communication.
(1) VL is powered by a separate LDO1, the level is 1.8V, and the signal on the VL side is 1.8V UART signals of two different ICs;
(2) VCC is powered by another separate LDO2, the level is 1.8V or 3.3V, and the signal on the VCC side is a 1.8V UART or a 3.3V UART;
(3) Because the UART signals of two different ICs need to be controlled, the IO power corresponding to the UART is not used as a reference level, but a separate LDO1 and LDO2 are used to provide a reference to ensure that the level is standard 1.8V or 3.3V.
(4) EN uses a separate 1.8V level enable, which may come from 5V or other voltage divisions. EN remains low for a long time. When UART communication is to be used, 1.8V enable level is provided.

over 3 years ago

0 Clemens Ladisch over 3 years ago

Guru 243220 points

The OE input is overvoltage tolerant; you do not need a voltage divider.

When EN is low, the eight inputs should not float to prevent shoot-through currents.

A direction-controlled translator like the SN74AXC4T245 would be cheaper and more robust.

0 Rami Mooti1 over 3 years ago

TI__Mastermind 23393 points

Dane,

You didn't present a question so I'm going to treat this as a review of your layout. If you had a specific question in mind, please don't hesitate to ask.

As Clemens mentioned, the OE input is overvoltage tolerant up to 5.5V so you won't need to use a voltage divider to bring down the voltage and your inputs shouldn't be left floating.
At your voltages, using a direction-controller translator as the SN74AXC4T245 may be a better fit, as you can also set the direction rather than having unutilized auto-directionality as the TXB offers. Here's an FAQ to help identify the best part for your need : [FAQ] Are there voltage level translation / level shifter device recommendations for the industry standard interfaces like GPIO, SPI, UART, I2C, MDIO, RGMII, I2S etc?

Thanks,
Rami

0 Dane Zhang over 3 years ago in reply to Rami Mooti1

TI__Expert 3420 points

Hi Mooti1,

could you help me to understand this:

When EN is low, the eight inputs should not float to prevent shoot-through currents

which may lead to the shoot-through current?

0 Clemens Ladisch over 3 years ago in reply to Dane Zhang

Guru 243220 points

When the output drivers are disabled, the voltages at the I/Os pins are floating. See [FAQ] How does a slow or floating input affect a CMOS device?

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TXB0104: TXB0104 application question