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Original question:

AMC1100: AMC1100 technology

AMC1100: AMC1100 random Offset issue.

Mr. PS
Prodigy 20 points

Part Number: AMC1100
Other Parts Discussed in Thread: AMC0300R, AMC0200R

  • We are using AMC1100 devices to measure two DC bus mid-point voltages in our system. Both measurement channels use the same circuit configuration (attached schematic).

    When the DC bus is balanced, both mid-point voltages should have the same value. Most of the time, the measurements are correct. However, we occasionally observe a difference between the two measured voltages, even though the actual DC bus voltages are equal and stable

    The offset appears randomly and is not consistently repeatable. We have not identified any specific operating condition that triggers it.

    We would like to understand:

    • Is there any known behavior of the AMC1100 that could cause such a random offset?
    • Could this be related to input bias currents, common-mode noise, transient events, power-supply fluctuations, or PCB layout differences between the two channels?
    • Are there any specific measurements or debug checks you would recommend to help identify the root cause?
    • Are there any known design considerations for DC bus midpoint sensing using AMC1100 that we should review?
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  • 0
    TI__Guru 59662 points

    Hi, 

    Where is the random offset observed and what is it's behavior once present? Does it remain static, oscillate or ramp? 

    In general, the differential to SE conversion OPA should have the same power supplies as the low side supply of the AMC1100. These +/-12V supplies could be creating a return current loop from the 5VA supply. 

    Have you considered a newer device with integrated conversion such as AMC0200R or AMC0300R? 

  • 0 in reply to Alexander Smith
    Prodigy 20 points

    Hi,

    We are observing the DC bus voltage through the microcontroller output, where the displayed value is a moving-average filtered measurement shown on the HMI.

    The issue has been observed during site operation in a grid-connected bidirectional converter. When the event occurs, the measured offset remains relatively stable for several minutes before returning to normal operation.

    Regarding the power supplies, the ±12 V supply and the 5VA supply share the same ground reference. We have not found any indication that the issue is related to the power supply, as isolated supplies are already being used in the design.

    At this stage, we have not considered migrating to a newer device because the problem is intermittent rather than permanent. The system operates normally most of the time, and the offset appears only occasionally.

  • 0 in reply to Alexander Smith
    Prodigy 20 points

    Hi Alexendar,

    We think the noise is coming through the DC bus as common-mode noise. Can we make any changes to the circuit to reduce this common-mode noise, and possibly the differential-mode noise as well?

  • 0 in reply to Mr. PS
    TI__Guru 59662 points

    Hi, 

    Without the layout or pictures of the offset, it's difficult for me to make too many recommendations.

    The common-mode noise rejection of the AMC1100 is quite high, so I doubt this is the issue, but it will be largely layout dependent. If the noise is common-mode noise resulting from layout, then this is a system level issue that should be addressed and understood. Moving the channel that has the issues away from the source of the issue in layout is a practical solution to consider. 

  • 0 in reply to Alexander Smith
    Prodigy 20 points

    Hi,

    We are currently working to capture and analyze the issue. However, since it occurs unpredictably, we have not yet been able to identify the root cause. To address this, we are attempting to replicate the condition through simulation to better understand what might be affecting the circuit. At the same time, we are closely monitoring the system to observe the conditions under which the issue arises