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AMC3330: Designing an Isolated ADC Circuit for ±50V Input by Swapping Terminals

cho byungkwan
Prodigy 30 points

Part Number: AMC3330
Other Parts Discussed in Thread: AMC0230D, AMC1311, , AMC1350, ISO224, AMC0211D

I am designing an isolated ADC circuit and would like to verify my front-end configuration.

My application requires measuring a range of -50V to +50V. Instead of using a standard negative voltage rail, I am planning to implement this by swapping the input wires, as shown in the attached image. Specifically, I will connect +50V to the INN pin and GND to the INP pin (this will be a low-speed, alternating crossover circuit).

I would like to know if the attached schematic is a valid approach for achieving a ±50V input range. Could you please provide guidance or a reference design for this use case?

Additionally, I have a few specific questions:

  1. Connection of INN and HGND: Is it mandatory to connect INN to HGND? Could you please explain the technical reason behind this requirement?

  2. Floating Inputs: What potential issues or risks (such as Common-Mode Voltage violations) might occur if I leave them unconnected?

  3. Device Compatibility: Can I apply this same design topology to the AMC3330, AMC0230D, and AMC1311, assuming I adjust the resistor values accordingly?

Thank you in advance for your help!

image.png

 

  • +1
    TI__Guru 60102 points

    Hi!

    1. No, connection to INN to HGND is not always necessary, but recommended to ensure that the inputs remain within the input common-mode voltage range to prevent inaccurate measurements or damage. This is accomplished with your split tap input connection however, so this is OK.

    2. Split tape input connection as designed should prevent any issues. 

    3. This should be fine with exception of AMC1311 since it has 0-2Vin and can only accept unipolar input. Please also consider AMC1350 and ISO224. 

    If testing for EMC, ferrite beads on the inputs may be necessary. www.ti.com/.../sbaa515a.pdf

  • 0 in reply to Alexander Smith
    Prodigy 30 points

    Thank you for the clear explanation and the helpful application note.

    Follow-up to your point about the split-tap connection: If I design the circuit with the mid-tap tied to HGND, does the system strictly require bipolar +/- inputs?

    Also, if I were to measure DC instead of AC signals under the exact same configuration, which ICs would you recommend? (Note: I am specifically looking for devices that support non-integrated DC-DC converter rather than a single power supply, similar to the AMC0230D).

    Thanks again for your guidance!

  • 0 in reply to cho byungkwan
    TI__Guru 60102 points

    Hi Cho, 

    Bipolar and differential inputs are required. Likely this is related to your other question. 

    Instead of DC vs AC, I would consider unipolar (0 to +V) or bipolar (+/-V). Unipolar could use a device such as AMC0211D. Give the input node swap problem statement as described in your other thread, you would need a device with bipolar input such as AMC0230D. This device cannot accept split-tap connection however.