[ADALM2000] maximum input voltage

[ADALM2000]

What is the maximum input voltage that can cause damage?
I want to know about analog input and digital input.



Add [ADALM2000]
[edited by: eokayama at 9:56 AM (GMT 0) on 16 Oct 2019]
Parents Reply Children
  • +1
    •  Analog Employees 
    on Aug 5, 2020 8:12 AM 8 months ago in reply to jaxankey

    Hi,

    The input voltage range of the ADALM2000 depends on the specificationd of AD9963 which is the converter that provides  the ADC channels (also the DAC channels).

    In the datasheet of AD9963 the full scale input range of the ADC is 1.56Vpp differential with an absolute maximum rating from -0.3V to 2.1V.

    The ADALM2000  gain range settings for the analog input voltage divider are:

    • High gain mode: for signals from -2.5 V to +2.5V with a total gain of 0.2756
    • Low gain mode: for signals from -25 V to 25 V with a total gain of 0.026

    If someone applies 25V while in the 2.5V range this means that at the ADC input pin the voltage will be 6.89V which exceeds the absolute maximum rating specified in datasheet and may cause damage.

    Given that the absolute maximum rating is 2.1V this means that in high gain mode one can apply up to 7.61Vpp differential  (-3.8V to +3.8V) and 80.7Vpp differential (-40.35 V to +40.35 V).

    You can find more information in the reference manual for ADALM2000:

    https://wiki.analog.com/university/tools/m2k/users/reference_manual#reference_manual_understanding_the_internals

    Regards,

    Andreea

  • 0
    •  Analog Employees 
    on Aug 5, 2020 11:31 AM 8 months ago in reply to andreeapop

    There is built in protection of the ADC pins provided by Schottky diodes. These  will clamp voltages above maximum ratings specified  in case of accidental connections, but you should always apply signals in the  range of the gain setting.

    Reconsidering what I said earlier about damaging the board when applying 25V in high gain mode, there may not be immediate damages because the voltage will be clamped. However, you should not rely only on this protection and use the suitable settings.

    Regards, 

    Andreea

  • 0
    •  Analog Employees 
    on Aug 5, 2020 1:19 PM 8 months ago in reply to jaxankey

    As was pointed out already there is an active clamp at the ADC inputs that protect that IC from over voltage on it's inputs. The actual worst case for over voltage on the inputs is driving the inputs of the range select analog CMOS switches beyond their supply voltage. The input current is limited by the 820K voltage divider resistor so things are in general fairly well protected. I would include part of the schematic but EZ is not allowing me to insert an image for some reason.

    Anyway there is a frequency compensation capacitor (c72) across the 820K resistor that will probably breakdown and fail first.

    Just my observations looking at the schematic. But as the manufacturer we can only insure proper operation when used within the provided input range specifications.

    Doug

  • Thanks everyone! I figured there was some protection or it would be hard to sell to undergrads. I'll tell them to start with the low-gain mode and only switch if they know it's safe to do so. Probably it won't pop, but if it does I'll let you know.