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TXB0104: TXB0104 input behavior

Part Number: TXB0104
Other Parts Discussed in Thread: SN74LVC2T45, SN74LVC1G17

To whom it may concern

We are using TXB0104D as level shifter between 5V domain and 3.3V domain

During initialization of the software we use PC5 (connected to TXB014 pin 13) as a board type detection signal (old board has a pull-down, new board has a pull-up).

The PC5 port from a MCU is during initialization set as output low for 10ms and then shifted to input and the SW will check the level after 30ms to distinguish between old boards and new boards.

But we have seen a strange behavior of the level shifter (U102) where it leaks approx. 400uA for some time after the falling edge of the signal (see attached oscilloscope screen shoot) preventing R145 to pull PC5 to 5V.

We have several boards and the timing seems to be component dependent ( timing from falling edge to rising edge vary from board to board, 20ms to more than 100ms)

If the trace between R145 and pin 13 is removed, PC5 is immediately pulled to 5V when the port is shifted from output to input.

The issue is seen both +3V3 is present and when +3V3 is not present

Can anyone comment what the root cause for the issue might be?
Or is this a normal behavior of TXB0104?

Regards

Henrik Leegaard