TLC5940: After running sometime with LED brightness increasing and decreasing, then TLC5940 died out

Part Number:TLC5940

Hi  This is a simple ardunio project with single chip TLC5940 running only 16 red leds.

I followed the tronixstuff tutorial.  I used the library by PaulStoffregen.

I used 2.2Kohm for IREF pin.

What could go wrong? 

I forgot to add ground line to VPRG, leaving it floating. It can't be the reason for this spoilt chip, isn't it?