Lindsay Lohan -- Lil Bro Shopping Spree #2 ... Drops ANOTHER $3,500

It's official ... Lindsay Lohan is a full-blown sugar mama -- at least to her little brother Cody -- because the actress dropped ANOTHER $3,500 this week on the 16-year-old ... and TMZ has the pics.

Lindsay and Cody hit up a Target in LA last weekend -- a day after Lindsay spent nearly $3,000 on Cody at a surf shop in Orange County -- and we're told ... she bought him a flat-screen TV, an iPod, and a digital camera.

The Target trip brings Lindsay's spending total to $6,223 this week alone.

According to sources, Cody is an aspiring pro surfer -- which explains the surf shop spending spree -- and we're told Lindsay wanted to reward him for doing so well.