Boost converter in series with buck LED driver
Do you have an alternative approach I haven't thought about?


Find a generic boost converter that can reliably produce 17 volts at 600 mA then, rearrange the feedback loop with your LEDs as part of it: -



The picture above uses a 12.4 ohm resistor and a FB voltage of 250 mV in order to get 20 mA but there's little stopping you using a 1.24 ohm resistor and getting 100 mA.

If you pick a generic booster that has a 0.8 volt reference voltage for feedback and you want 600 mA to flow, the resistor would need to be 1.333 ohms.