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I am looking at powering a PoE circuit that drives a 24V motor at 2A. I am considering the LT4275/LT4276 LTPoE++™ Controller. I noticed on the datasheet for the controller LT4275 they recommend an "isolated" DC/DC converter but in the eval board documentation they don't mention "isolated" DC/DC converter.

Is an isolation DC/DC converter just mentioned as best practice? What would happen if you use a non-isolated DC/DC converter?

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You need an isolated converter when the device should be floating instead of referenced to the ground of the PoE injector.

Since the injector may be in a different room or building, and thus may have a different ground than the one the device is placed in, no exposed parts may be connected to the circuit ground reference if you are not using an isolated converter.

This is similar to Grounding a POE-powered device.

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  • \$\begingroup\$ So if the only device I am running is a standalone motor circuit with no other devices, I can get away with a non-isolated dc/dc converter? @simon-richter \$\endgroup\$ – be-ee Jul 12 at 16:43
  • \$\begingroup\$ @be-ee, if the user cannot touch anything that is referenced to that voltage. \$\endgroup\$ – Simon Richter Jul 12 at 20:14
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A motor would not need an isolated converter. If your using any electronics that would need to be referenced to ground, an isolated converter would be needed. If your only using a motor for a load, then the motor will not care what it's negative terminal is referenced to.

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