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ADG4612 isolation mode negative condition failed after two power up

Question asked by jpl on Jul 5, 2015
Latest reply on Aug 10, 2015 by Stephen_Nugent

Hello,

 

I use a ADG4612 with 0V on GND pin and Vss pin, and +8V on Vdd pin for the on condition. All INx are connected to +8V also at the same time on power up.

 

Initial step : (power supply OFF) Vdd floating ,INx floating. and Dx floating

Second step : (power supply OFF) Vdd floating, INx floating and D4 with negative voltage between 0V and -5,5V. I measure 0V on S4.

Third step : (power supply ON) Vdd +8V,INx +8V. and D4 with negative voltage between 0V and -5,5V. I measure the same voltage on S4.

Fourth step : (power supply OFF) Vdd floating ,INx floating. and D4 still with same negative voltage between 0V and -5,5V. I measure then a negative voltage on S4, a bit less than the one on D4.

 

So as far as I can see, the isolation mode works for the negative condition only if previously the signal was floating or near 0V. This behaviour does not occur with positive signal.

 

Is this normal ? I would expect to see 0V on S4 at step 4.

 

Thank you.

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