ADS4245: Live Signals on the Input When Not Powered

Hi,

The person who is supporting this is out of office at the moment, but it is possible over time for the part to be damaged, yes.  The abs max section of the datasheet lists the max voltage on the clock and analog inputs as supply + 0.3V.   This is the limit under which the ESD diodes do not turn on.   Above that the ESD diodes may turn on and in the worst case may try to pull enough current through these inputs to try to power up the whole device.    If the signal source for these inputs is inherently current limited then this may not be a problem short term.  But if the signal source is able to supply lots of current then this could very much be a problem.   In the lab during evaluations we may have the analog inputs present without the power supply on, but through coax from a 50 ohm source the current is inherently limited and does not present an issue short term.   I say short term because in that bench environment we are not interested in whether we shortened the expected lifetime reliability of the device by doing so.  Long term, violating the abs max specs *may* affect lifetime reliability if the violation exists for 1) a long time, 2) often and repetitively, or 3) is a large violation of the specs rather than a 'little' bit out of spec. 

I notice in the datasheet that the CMOS control signals are simply limited to 3.9V regardless of supply, so these signals could very well be present in the absence of supply.   But clock and analog inputs do run the risk of affecting reliability of the device if the abs max specs are violated.

Regards,

Richard P.

Richard,

Thanks for your quick response!

I will let you know if the customer has any further questions.

Richard Elmquist