ICL8820 is there an application note for constant current control of led drivers ?  is this i.c. the best choice for a 50 w cc led driver.  

I am considering providing backup power to the Vcc pin of the ILD8150XUMA1. Under normal circumstances, we plan to supply approximately 60V to the Vin pin. However, there are potential fault conditions where the voltage may drop to as low as 1V. In such situations, we want the internal logic of the chip to continue functioning normally. My question is: Will supplying a backup voltage of around 6.8V to the Vcc pin in the absence of Vin cause any issues or complications?

I understand VCC provides the output voltage from internal regulator but still can this be use to provide 6.8V externally.