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TXB0108 Logic Translator Problem: Low output

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thobson

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Hi,

I'm trying to use a TXB0108 (www.ti.com/lit/ds/symlink/txb0108.pdf) bidirectional logic translator to convert 5V to 3.3V and vice versa. When I send a 5Vpp time-varying digital input (like a square wave) to the 5V side, I don't get the same signal at 3.3Vpp on the output side. What I get is a signal that toggles with the input, but is only ~25mVpp centered around ~1.5V. However, the chip has no problem converting DC voltages up/down. Only when the signal toggles do I get this odd behaviour.

The settings are: Vcca=3.3V, Vccb = 5V, OE = 3.3V.

I've read that a load on the output of this chip can cause problems, but there isn't much of a load on the output, and I get the same behaviour using a completely disconnected/unloaded output.

Could this be a sign that the part is damaged, or might there be some other problem?

Thanks!
 

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