LM3478 Boost Converter

[Signal Simon]

I've made a couple of successful LM3478-based boost converters for obtaining 5V and 12V rails in a portable device powered by 3 AA Cells.
The 12V is enabled/shutdown by the micro as required, which saves about 7mA - "You could fly to the moon on that" as Dave would say.
Component selection primarily based on Webench, but substituting easily hand-worked component variants, eg 0805 passives and SO-8 IC and FET.

Next project is a pocket power supply that will deliver 24V at 300mA or 50V at 150mA (switchable) from 4 AA Cells.
The ideal scenario is that I only want to switch in a parallel resistor to the feedback network to select output voltage.

However, the suggested compensation network values have ranges which do not overlap.

One solution I have found (in theory!!), is to run the converter at 100kHz in the 50V mode and at 120kHz in the 24V mode, by switching in an extra 47K on the FA pin, which then means I can just switch in an extra 2K2 on the Comp pin, as the suggested values for Ccomp 1 and Ccomp2 then remain the same.

Do I need to go to the trouble of an extra 2 mosfets and resistors, or can I just run at 100kHz and go with the larger compensation components for lower crossover frequency, as that's what the app note seems to imply?

I've mashed my head with the old National Semiconductor Application Note AN-1286 and right half plane zeros!

Simon.