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I am currently working on a project that involves using the TXB0104PWR level shifter for signal conversion. In the diagram provided, the OE pin of the level shifter is connected to a resistor going to ground. The value of the resistor is unspecified in the diagram. I am confused about how to pull the OE pin high to enable the outputs of the level shifter.

My understanding is that pulling the OE pin low would enable the tri-state mode, placing the outputs in a high-impedance state. However, I need to actively drive signals onto the bus, so I want to pull the OE pin high to enable the outputs.

How can I achieve this? Should I connect the OE pin to ground as shown in the diagram, or is there a different method to pull the OE pin high? If so, what value resistor should I use and how should it be connected, also shown is a connection from OE to the controller, what might this be?

I appreciate any clarification or guidance on properly pulling the OE pin high on the TXB0104PWR level shifter. Thank you in advance for your help!

TXB0104 typical application

Ashton Scott
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  • You commented this will be used for USB UART to ATMega. For an UART, why would you need a level shifter to begin with? Use same voltage on both chips and you don't need level shifting. What levels you are using then, or are they variable? AVR can run on 3.3V for 3.3V USB IO, and some USB chips support 5V IO. There are also AVRs and other MCUs with built-in USB so one chip can do the job of two chips plus level converter. – Justme Jun 12 '23 at 13:04

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In the original diagram, the OE does have a pull-down resistor, but it is also controlled by a logic signal from the 1.8V device.

If you don't need the disable feature then connect it to logic high voltage directly. Simple as that.

But a word of warning, if you don't use the chip exactly as specified in the data sheet, your next question will be why your level shifter does not work properly and the answer is you are using the chip incorrectly or it's the wrong chip for the job. You might want to open a new question where you post your intended circuit and ask if the chip is used correctly.

Justme
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The datasheet says:

To ensure the high-impedance state during power up or power down, OE must be tied to GND through a pulldown resistor.

If you do not care about the state of the outputs during power up or power down, then you can connect OE directly to VCCA.

The example shows the OE signal connected to a microcontroller. The software on the microcontroller would set the signal high whenever it decides to activate the connection to the 3.3 system.

(Please note that the auto-bidirectional architecture of the TXB makes it unsuitable for many applications; you should use it only if your signals actually are bidirectional, without a direction-control signal.)

CL.
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  • I'm planning to use the TXB0104PWR level shifter chip for a USB to UART application with an ATMEGA328P. Is this chip suitable for this 'application'? Note I'm way out of my depth here (only a beginner in this kind of design) so again any help is much appreciated. – Ashton Scott Jun 12 '23 at 06:15
  • UART signals are unidirectional. Consider something like the TXU0202. – CL. Jun 12 '23 at 07:39