Kjwinden :
650 bronze rated to be safe.
500W would be enough for an unoverclocked system, provided that most of the 500W can be supplied on the 12V rail.
OP, it'll be helpful if you told us what particular model your power supply is, and the amount of amps on the 12V rail before we can give you an accurate assessment. There aren't alot of 520W PSU's on the market, so it sounds like its from Seasonic or Antec to me.
Also, I wouldn't really recommend putting an A10 with a 7970, just seems out of place (Since trinity is mostly bought for its internal GPU).