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Noise on LT8652S and LT8364 outputs

Hello,

I am using a LT8652S and a LT8364 to generate +15V, +5V and -15V from 18V.

Overall its working, but I am measuring some noise (not switching noise) on the +-15V outputs, which I cant really identify. Also the +5V output starts oscillating at >0.5A at 300kHz.

I have attached the schematic, the layout is mostly as in the application notes. In LTspice aswell as LTpowerCAD it simulates just fine, without the noise.

I took the meaurements with 1.5A at +15V, 1A at -15V and 1A at +5V using the tip & barrel method on the output caps. The switching frequency is about 1.8 MHz,

Can anybody help me with that?

PDF

+15V at 1.5A 50uS measurement:

+15V at 1.5A 1uS measurement:

-15V at 1A 50uS measurement:

-15V at 1A 1uS measurement:

+5V at 1A 50uS measurement:

+5V at 1A 1uS measurement: