Intel 31244 PCI-X manual Power Distribution and Decoupling

Intel® 31244 PCI-X to Serial ATA Controller

Routing Guidelines

4.4Power Distribution and Decoupling

Have ample decoupling to ground, for the power planes, to minimize the effects of the switching currents. Three types of decoupling are: the bulk, the high-frequency ceramic, and the inter-plane capacitors.

•Bulk capacitance consist of electrolytic or tantalum capacitors. These capacitors supply large reservoirs of charge, but they are useful only at lower frequencies due to lead inductance effects. The bulk capacitors may be located anywhere on the board.

•For fast switching currents, high-frequency low-inductance capacitors are most effective. Place these capacitors as close to the device being decoupled as possible. This minimizes the parasitic resistance and inductance associated with board traces and vias.

•Use an inter-plane capacitor between power and ground planes to reduce the effective plane impedance at high frequencies. The general guideline for placing capacitors is to place high-frequency ceramic capacitors as close as possible to the module.

4.4.1Decoupling

Inadequate high-frequency decoupling results in intermittent and unreliable behavior. A general guideline recommends that you use the largest easily available capacitor in the lowest inductance package.

4.4.1.1Intel® 31244 PCI-X to Serial ATA Controller Decoupling

It is recommended that to decouple the VCC 2.5 V, use at least twelve 0.1 µF capacitors in as close proximity to the GD31244 VCC pins as possible. When feasible, locate these capacitors on the back of the board, close to the GD31244 VCC ball.

28 Design Guide