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SM72485 unstable at different supply voltages

Just starting to play with this ic.

It is configured to output 5v (rfb1 = 10k, rfb2 = 10k).  It also has a 630uH inductor on the switch.

There is a 1 ohm that feeds inductor current to a 470uF cap on the output side.  The feedback divider as stated is pre this one ohm so that the ic sees ripple as needed.

IC will deliver 5v and traces on the output line look stable and clean between 6v and 20v DC supply.

But above 20v I start to see saw shaped dips on the output voltage that appear to last 100-120ms.

The output load current is from 3mA to 60mA.

Can anyone give advice?  This is supposed to output 5v from 7v to 75V!  So far it's looking bad.

Many thanks.