LM3100 Output Voltage

We use the LM3100 for dc/dc conversion from 24 V to 5 V (see schematic, calculated output voltage: 0.8 V*(1+6.81/(2.61/2)=4.975 V). It works, but the output voltage is not as constant as told in the data sheet. The output voltage is stable (very little switching noise to see) but it changes its dc value depending on the load:

Little load (approx. 250 mA, discontinuous mode): output voltage 5.09 V
approx. 1 A load: output voltage: 4.89 V.

So we get a difference of 200 mV between light and normal load. The feedback voltage at the feedback pin changes in the same way. What's wrong in our design? The layout is done the way described in the data sheet (resistive feedback divider close to the voltage feedback input pin, 4-layer with ground plane, no ground voltage difference at different points in the layout to measure).

Best regards,
Edwin Krasser

Here is the schematic:

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