AD780 +Vin Pin and DNC Pin Problem

Hi All,

End user raised up the below question for un-powered I-V curve tracing with input voltage between both -5V to 5V and -1.5 V to 1.5V. No application or on-board test result available. 

According to the un-powered curve tracing, pin 2 (Vin-power pin) shows slight inconsistencies among all the 4 test samples. Does this level of inconsistency indicate leakage on Vin? And will it affect the functional stability for the output voltage? 

Input: -5V to 5V   Pin 2-Vin                                                                                     Input: -1.5V to 1.5V Pin 2-Vin


In addition, user tested DNC pins and found below. Although I know DNC pins should be left floating on the board, user tested them also for un-powered curve tracing:

Pin 1-DNC -5V to 5V                                                                                Pin -DNC -1.5 V to 1.5V


Does Pin 1 is defined as DNC, will the inconsistency on I-V affect the functionality to any extent? Appreciate if you can help clarify the above questions. Thanks!

  • +1
    •  Analog Employees 
    on Jul 23, 2019 3:09 AM

    Hi SLee124,

    Is there any reason regarding the checking of the Curve Trace? Are you experiencing some problem in using the part? If so, let us know.

    Regarding your curve tracing, the Vin pin of the AD780 is rated to operate at 4V to 36V. It is not recommended to apply negative voltage in this pin as it might damage the device. The same also apply for the DNC pin, this pin is used as a production test pin, so applying any kind of voltage in this pin might damage the device.

    Normally curve tracing is used to have a quick check of the diode at the pin. So if you look at your measurement at Vin pin, the response is just like a diode trace. 

    Could I know at what pin you read these graph? Because the curve trace signature depends where you put the probe for measuring the trace.

    Best Regards,