I just finished using the K26 in a previous design and am planning for the KL26 in a lower power version. The documentation in the KL26, however, is not as clear about how the VREGIN power is utilized internally to the chip as is the K26. I assume they are the same, but figured it would be better to ask just in case. Specifically, the K26 user's manual shows and states that the USB VREG is the power source for the USB transceivers (See figures 50-2, 50-3, 52-1). In other words, if you don't put 5V on VREGIN, you won't be able to communicate over USB. Further, the USB transceivers are only powered when a voltage is on VREGIN (i.e. if I power the rest of the chip with a supply from an external source such as a battery, the USB transceivers do not consume any power from the battery, only from the USB power that is connected to VREGIN).
The KL26 datasheet does not make this as clear. I can't find any pictures in the KL26 that were similar to those found in the K26, and nowhere does it explicitly state that the VREGIN powers the USB transceivers. The only figure that is close is Figure 36-2 in the KL26 datasheet which has an "Other Modules" block that is not very informative.
I did find another question on the forums that suggested someone had neglected to wire up the VREGIN power and couldn't get it to communicate, but the thread was never officially resolved.
Can anyone confirm that the USB Transceivers in the KL26 are solely powered by the internal USB VREG output?