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AMC1305L25: Output signal fixed at 1.25V

Sebastian Neira
Prodigy 10 points
Part Number: AMC1305L25

Hello everyone,

We are testing the AMC1305L25 ADC and both output signals are fixed at 1.25V regardless the voltage variations that we apply in the input. We are using a 10 MHz clock signal that we checked is correctly connected to the respective pins. We have also checked that power supply at both sides is correct. 

Has anyone faced a similar problem with this ADC?

Hope you can help us, 

Regards!

  • 0
    TI__Mastermind 31655 points

    Hello Sebastian,

    Can you provide a schematic showing the connections to your AMC1305 device? The output common mode of the device is supposed to be around 1.25V, but you should see it switching at the CLKIN frequency to generate the bitstream with highs and lows proportional to your differential input. Can you also please post a scope capture of the output?

    (Note, I edited my previous response because I mistakenly thought you were using the CMOS version. Please ignore that response if you have gotten the email notification)

    Regards,

    Scott

  • 0 in reply to Scott Cummins
    Prodigy 10 points

    Hello Scott,

    Thanks for your reply. Here you can see the clock signal inputs and the output fixed at the common mode value. Also we attach the schematic of our implementation. We are trying to measure a voltage following the application example in the datasheet, VADC-  and HB- inputs are connected in the outer file, so the input should be corrected referenced to the analog ground.

    Regards,

  • 0 in reply to Sebastian Neira
    TI__Mastermind 31655 points

    Hi Sebastian,


    Thank you for the additional information. I will be reviewing this and I will get back to you next week.


    Regards,

  • 0
    Prodigy 10 points

    Hello!

    We have changed the IC and the behavior improved, but still is not working properly. Apparently, now it's reading a full-scale input, which shouldn't be the case as we are applying a 0V input (which lies between range). Have anyone faced similar issues with this ADC? 

    Attached are the pictures of the output we are obtaining, corresponding to 1 pulse every 128 bits.

    Regards,

  • 0 in reply to Sebastian Neira
    TI__Mastermind 31655 points

    Hi Sebastian,

    The output does appear to show that the input is clipping. To fully eliminate any source of the behavior outside of the AMC1305, can you connect AINN directly to AGND and short the inputs AINN and AINP? This will guarantee a 0V input and we can determine if the AMC1305 is functioning properly. You should see a bitstream output with roughly 50% ones.

    Regards,

  • 0 in reply to Scott Cummins
    Prodigy 110 points

    Hello Scott, 

    we just tried shorting the pins as you suggested. We still get the clipping pulse every 128 clock cycles - no 50% bitstream.

    Kind regards, 

    Zoe and Sebastian