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TXS0108E: Are the inputs 5V tolerant ?

Part Number: TXS0108E
Other Parts Discussed in Thread: TXU0104, SN74LVC541A, SN74LXC8T245

We are currently using the TXS0108E to translate from 3V3 to 1V8 from B inputs to A outputs (VCCB=3V3, VCCa=1V8), unidirectional operation.

We are looking at a temporary design change in which one of the B inputs will be driven to 5V (VCCB still 3V3).

I note in the electrical specifications that during normal operation, the B input is only allowed to drive to VCCI, or VCCB, ie 3V3, even though the absolute maximum allowed voltage at B is 5.5V.

What is the consequence of applying a 5V signal to the B input when VCCB is 3V3? Is this allowed even though the datasheet specifies not to do it ?

Thanks.

  • The TXS is a passive switch. "Input" and "output" probably means the edge accelerators.

    Anyway, all A/B pins are both inputs and outputs; the wider input voltage matters only when the outputs are disabled. The VCC+0.5V specification implies that there is a clamping diode from the pin to VCC.

    For unidirectional signals, a simpler solution would be a unidirectional level translator (2× TXU0104) or simply a buffer with overvoltage-tolerant inputs like the SN74LVC541A.

  • Thanks Clemens

    That has predominately answered my question. I specified inputs and outputs since for our application we are indeed only translating in one direction (unidirectional). I was looking at whether rework was possible for the TXS0108E before updating the design to use a more suitable device such as the devices you mention. Your answer has answer has confirmed my suspicions. It is non ideal for the input clamp diode to conduct since "latchup" is always possible, so not really an option. I was also considering the SN74LXC8T245 device, but unidirectionally by tying the DIR pin appropriately.

    Thanks again for your prompt response.