We managed to get a few more details about Intel’s one-chip Haswell platform that people internally also call Haswell ULT. ULT means that the part operates on ultra-low voltage and is quite self-explanatory. The main difference between one-chip and two-chip Haswell mobile CPUs is that the one chip part has the Lynx point LP PCH chipset inside of the CPU package. One can view this chip as a SoC (System on chip) and it will come in BGA package. 

Intel also referred to this chip as part of its Y-processor line of products, with a 11.5W maximum TDP and scenario design power of 7.5W. This is quite exceptional considering that this is the TDP of the complete SoC. In contrast, the Ivy Bridge Y-processor line had a 13W TDP (7W SDP), and that was only the CPU.

The point of having a BGA package and making a SoC is to lower the production cost, lower TDP and footprint. Haswell ULT is the chip meant for Ultrabooks and tablets where footprint, TDP and lower cost play a key role. This is probably why Intel plans to further drop the Haswell Ultrabooks pricing, as mentioned here.

Intel promises eight to ten hours of endurance with Haswell ULT based tablets and the lowest TDP we saw in Intel’s future plans was 15W, but maybe Intel can go even lower in the future. The plan is to see some of these Haswell ULT devices in Q4 2013 and onwards, while Ultrabook U-series parts will show up one quarter earlier.