High voltage Isolation & ADC sensing

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Joined Mar 23, 2016

I'm creating a closed-loop controller to be used in medium voltage applications which can have bus voltages that exceed 10 kV. As such, isolation is very important.

For sensing voltages, I've become privy to the AMC1336-Q1 (https://www.ti.com/lit/ds/symlink/amc1336-q1.pdf?ts=1614579250739&ref_url=https%3A%2F%2Fwww.ti.com%2Fproduct%2FAMC1336-Q1). It's got a 1.5 GOhm input impedance, a simple 8-pin layout, does not require the use of any amplifier circuits, and has good documentation on the digital filter and bitstream. I haven't been able to find any other device like it.

However, one of its features becomes a drawback for me. I'm really looking for working isolation voltages of at least 10 kV. This device has a built-in isolation layer that is only 8 kV peak, 5.7 kV RMS (1min). That's not high enough. The thing is, I don't even need that isolation barrier -- my DC/DC supply is rated for 20 kV isolation and my digital isolation is rated for 27kV+ isolation.

My big question is: Do you think it would be ok to connect the ground plane across the isolation barrier of this device, or would that ruin its basic functionality?

I've attached two figures to demonstrate what I'm talking about.

There's also the approach of finding another FDA/ADC combo that does not have any isolation barriers but also has a high imput impedance like this device does. It's probably the best approach because I just really don't know if this device will function properly if the isolation is bypassed. If anyone here knows, that would be great. I just hate having to use FDAs when I can avoid it; they always add an extra layer of complexity and problems to these designs.

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