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TXB0108: Level Translator functionality

Part Number: TXB0108
Other Parts Discussed in Thread: TXU0304, TXU0104, TXU0204


I'm using a TXB0108  level translator for the Logic conversion from 1.8V to 3.3V. The SoC is referred to 1.8V Logic and External GPIO Header referred to 3.3V Logic.

I'm configuring the 2 I/Os of TXB0108 as INPUT to the SoC and having internal pull down of 100KΩ. So my driving source is the corresponding pins at the GPIO Header.

Case1: While probing at both sides of TXB0108, without any driving source from the corresponding pins of the GPIO Header during the boot up of the board itself, Sometimes I'm observing the 3.3V at the Header and 1.8V at the SoC.

So What could be the reason for the sometimes HIGH Level Logic without any driving source during the boot up of the board itself even I had enabled the Internal Pull down of 100KΩ at the SoC?

Case2: Adding to that, I had a given a square wave of 3.3V logic to the configured Input pins and I'm observed the exact level translation to 1.8V.

Whenever I'm having a defined HIGH / LOW state ,I'm getting the proper response and if the input driven with HIGH output also HIGH and if the source got disconnected (Floating),still the LT gives a HIGH signal even Internal pull down enabled at the SoC.