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Latch up?

Question asked by javaman on May 9, 2012
Latest reply on May 23, 2012 by FEB

I'm translating a 3.3v GPS TX to an OMAP uP 1.8v Rx line using the ADG3308. When I connect the TX signal to the translator it tries to drive the line high causing a funky serial waveform over a DC level between 2-3 volts, 3.3volts overall. The opposite side of the driver is also high at 1.8V. During power on both lines stay low. I tried adding a 1M pull down resistor to both sides of the translator but it still tries to drive the wrong direction when a signal is applied. I am pulling the enable line to 3.3v. I replaced the ADG3308 thinking it might be bad but it still operated the same way. I can remove the uP and  the ADG3308 still does not drive the serial signal but drives that line to a "high" state. I also have 3 unused ports that are grounded on the low side.

 

Any ideas would be most helpful, I have a board full of these parts and everything else is working.

 

Thanks

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