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TXB0106: Adding series resistance to the TXB0106RGYR

Martin Trainer
Prodigy 90 points

Part Number: TXB0106
Other Parts Discussed in Thread: TXU0204, TXU0101

Hello,

We have an application where we are running RS232 and RS485 signals through the TXB0106RGYR to level shift between 2.5V and 3.3V. It is unidirectional, but the bidirectional TXB0106RGYR has been picked to combine 5 signals into a single package.

For our design, we need to place series resistors between the MCU and the level shifter to limit the power injected into the MCU in fault scenarios. the resistor values need to be at least 1K, but it would be better to be 10K. Below is the application layout.

I would like to understand what the maximim limit is for the series resistances to ensure that voltage input high threshold is respected. What drive current is typical on an input? 

image.png

  • 0
    Guru 325980 points

    As shown in section 7.3.2 of the datasheet, input signals must have a drive strength of at least 2 mA. So the resistor must be much smaller than 625 Ω.

    Unidirectional level shifters like the TXU0204/TXU0101 would be a better idea.