AD8130: Overvoltage

Document created by analog-archivist Employee on Feb 23, 2016
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It could happen the system is switched off while the input video signal is
still present.
This means the input amplifiers AD8130 see a voltage at there input pins while
the supply voltage is switched off.
The video signal is DC coupled with an amplitude of about 2.5V. In serial to
the inputs of the AD8130 are resistors with a current value of 1K. But these
resistor values must be reduced by the customer. So he needs the information
what is the maximum value of the current that could flow in/out of the inputs
of the AD8130.

Unfortunately this is not specified in the Datasheet. On page 21 of the
datasheet right column it is mentioned: "For this and other reasons, it is not
recommended to reverse the input and feedback stages of the AD8129/AD8130, even
though some apparently normal functionality might be observed under some
conditions."

 

The maximum current into any of the AD8130 inputs with power off is 5 mA.  This
current flows in the ESD protection diodes, and the max value is based on metal
migration issues.

The AD8130 applications engineer has written a document that deals with
providing common-mode protection to the AD8130 inputs with Schottky diodes when
signals are applied and power is not.



When the device is powered, the input to any pin must be less than 0.3V over
the respective supply -- this is indicated in the Abs Max section of the
datasheet.  When the device is unpowered, the same is essentially true.  If
sufficiently large series resistors are used to keep the current under 5 mA
when the ESD diodes kick in, it's okay. 

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