On Board Power Regulation; Capacitive Decoupling; Figure 2-9. Example Of Via Location - VIA Technologies Apollo Pro133A Design Manual

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Design Guide - VT82C694X Apollo Pro133 with VT82C686A
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2.2.4 On Board Power Regulation

Currently, the voltage range of the Slot-1 processor core voltage (VCC_CORE) is between 2.1V and 3.3V. And the voltage range
of the Socket-370 processor core voltage is between 1.3V to 2.05V. Local regulation of VCC_CORE is recommended. That is, a
local DC-to-DC converter, placed as close to the CPU as possible, converts a higher voltage to a lower voltage using a linear or
switching (preferred) regulator. Bulk decoupling capacitors (greater than 10uF, Electrolytic or Tantalum) are used to prevent
power supply droop. The closer to the load the capacitor is placed, the more inductance is bypassed.

2.2.5 Capacitive Decoupling

This section describes issues related to the capacitive decoupling of a Slot-1 CPU, Socket-370 CPU, Apollo Pro133A chipsets and
DRAM Modules. It is well known that appropriate decoupling capacitors are required to provide a stable power source to the
CPU, the ASIC and all other components on a motherboard. Moreover, details about capacitor type and placement on a
motherboard are also given.
Decoupling capacitors are required to provide a stable power source to a CPU on a motherboard. Usually, low ESR and low ESL
capacitors are preferred for decoupling. High frequency decoupling capacitors (less than 10uF, ceramic) are used to provide
adequate decouplings. For example, 0.1uF, 1uF and 4.7uF capacitors can be treated as high frequency decoupling capacitors. It is
recommended to keep vias for decoupling capacitors (SMD type) as close to the capacitor pads as possible (see Figure 2-9).

Figure 2-9. Example of Via Location

Preliminary Revision 0.5, November 19, 1999 17 Motherboard Design Guidelines