Downs has been a bright spot on an otherwise struggling Angels team this season, going 2-3 with a 1.84 ERA in 43 games. The left-hander's streak of 29 consecutive scoreless appearances was snapped last week.
In exchange, the Angels obtained relief pitcher Cory Rasmus.
Downs, who has spent time with the Chicago Cubs, Montreal Expos, Toronto Blue Jays and the Angels in his 539-game career, sports overall marks of 36-35 with 26 saves and a 3.47 ERA.
Rasmus, 25-year-old right-hander, is a former first-round Braves draft pick. He has made three relief appearances for Atlanta this year while posting a 1.72 ERA in 37 games with Class AAA Gwinnett this season.
The hurler is the younger brother of Toronto Blue Jays center fielder Colby Rasmus.