I have essentially duplicated Figure 15 of the LM2840 Datasheet. I'm using the LM2841X. I did a careful layout heeding the guidelines. Above a certain input voltage, the output does not regulate when started using the Enable pin unless it is loaded. As I increase the input voltage, the output fails to regulate on startup even when loaded. I tried a soft-start circuit (100K ohms and 0.1uF) but it didn't seem to make any difference. Any suggestions?