VRM Clock

Hello friends.
Have card ASUS ROG MATRIX GeForce GTX980 4G , always use the software from ASUS for overclocking GPU Tweak II. There is an option that I never touched and don't know what she gives , called VRM Clock.

So , if anyone knows , what is the frequency of this VRM, and what is it , please tell me , I tried to Google ,but to no avail , this particular setting can not be found.