S. Abe, M. Hirokawa (Japan), T. Zaitsu (USA), and T. Ninomiya (Japan)
: Disturbed power system, bus converter, POL, stability, input impedance, output impedance
: The bus architecture, consisting of bus converter and POLs (Point Of Load), has become very popular since POL can respond to some demands of multi power supply voltage, low driving voltage and series sequence/tracking of LSI with more flexibility than isolated DC-DC solution. However, the customer suffers the system unstability issue caused by impedance overlap between the bus converter and POL. Bus converter has three types i)Un-regulated, ii)Semi-regulated, iii)Full-regulated, and each type has different output char acteristic. This makes matter more complex to understand and difficult to resolve the instability phenomena. This pa per investigates the comparison of the stability of three types of bus converter and POL using steady state average model. As a result, it has been found that "un-regulated bus converter+POL" is the most stable, "Full-regulated bus converter+POL" is next due to dumping of the resonant peak of impedance by the loop feedback, "Semi-regulated bus converter+POL" is the most un-stable, therefore a large ca pacitor at the intermediate bus is needed.
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