Enpirion has two DC-DC converters for DDR2/DDR3 VTT memory module applications.

The 8A EV1380 and the 4A EV1340 switch-mode converters achieve up to 94% efficiency and integrate the inductor, power switches, gate drive, controller, and loop compensation, in a QFN package: (8A) 8 mm x 11 mm x 3mm and (4A) 10 mm x 5.5 mm x 3 mm.  

Two EV1380 (8A) parts can be paralleled to support VTT applications up to 16A

For more information, see http://www.enpirion.com