Chris- I think you are in violent agreement with Larry and others with regard to this thread's topic. You are saying that p/s dynamic response is just as important as the impedance. If you look at the output impedance of a VRM it will exhibit some low impedance from DC up to some corner frequency that is a function of the loop dynamics (i.e. loop bandwidth) . Above that corner frequency the impedance will begin to climb. VRM's that have a higher clock frequency usually have a correspondingly higher corner frequency at which the impedance starts to increase. Hence, one can argue that VRM's with higher clock frequencies maintain a low output impedance to higher frequencies than VRMs with lower clock frequencies. It follows as you have pointed out, that a smaller amount of bulk capacitance is required to maintain a low impedance over the low end of the spectrum when the VRM maintains it's impedance at a low value to a higher frequency. As far as "one of these days" a VRM with a 10-100MHz clock rate becoming available, I think "one of these days" has already arrived. (Check out some of the available VRM's aimed at the military market and the multi-phase switchers that have a high "effective" clock rate due to the multi-phase architecture). So, are we in violent agreement or am I misinterpreting your statement? -Ray Chris Cheng wrote: >I think the power supply response is just as important as the impedance. If >you can get your DC/DC to beat faster, the amount of bulk caps needed to >hold the low end of the impedance can be minimized. One of these days, some >very smart people will come out with a 10-100MHz DC/DC. Things will get very >interesting. > > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu