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OPA344: What is the cause and what is the solution for this strange conditioner?

Part Number: OPA344
Other Parts Discussed in Thread: LM2576

Hi Ras,

sorry for being late, but I was very busy in my job.

There's a mistake in your PCB: The switcher LM2576 and the rest circuitry should not share the same ground plane! Instead, use for the L2576 a local ground and connect it to the global ground plane at only one place. The datasheet contains a layout example for the LM2576. Make the connection to the global ground plane where I painted the red circle:

With this technique you prevent the noisy switching currents of LM2576 from contaminating the analog ground.