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TPS7A47: Oscillation on the specific load

Part Number: TPS7A47
Other Parts Discussed in Thread: LM5164

I'm testing a PSU that is a 42V to 19V buck converter (LM5164) and an LDO (TPS7A4700) to get a clean 18V.

Everything is fine until the LDO sees a load of ~0.4A. With this load I see a strong 10MHz oscillation on the output rail (approximately 10mV pp). The oscillation gets stronger if the load increases. What may be the cause of such behaviour?

I didn't include the tantalum input cap because the LDO is very close to the buck output. The output of the buck converter is filtered with a PI filter (0.1uF -> ferrite bead-> 1uF).