using two LTC3780 in parallel

I'd like to use two of these in parallel. Has anyone done this? It seems as simple as supplying a 200-400KHz clock to PLLIN pin. The data sheet doesn't specify how clean that clock input should be. How does one generate a 200-400 KHz clock anyway? A crystal oscillator and a divider sounds like the simplest solution. Any experience with the part and/or suggestions are welcome.