Intel
®
EP80579 Integrated Processor Product Line—System Power Delivery Guide
Intel
®
EP80579 Integrated Processor Product Line
Platform Design Guide May 2010
76 Order Number: 320068-005US
6.6.3.5 General Layout Recommendations
All of the components in the high current paths dissipate some power (i.e., they get
warm when current runs through them). To minimize temperature rise and facilitate
thermal spreading, use of large copper fill areas connecting the high current
components is imperative. For example, the MOSFET manufacturers recommend that
each MOSFET be mounted on one square inch of two-ounce copper. While this may not
be possible in all environments, this recommendation serves to illustrate the
importance of thermal considerations in the switching regulator layout.
• Bulk capacitors for V
CC
need at least three vias per pad and it is recommended not
to share vias. Clusters of bulk and bypass capacitors may be clustered along the
high current paths between the sense resistor and the processor. Clusters may
have copper fill areas between capacitors. This provides additional opportunities for
as many vias as possible.
• Some controllers sense the load on Vcc by monitoring the voltage drop across the
sense resistor with a Kelvin connection. The two feedback traces do not handle a
high current, but must be of equal lengths to get an accurate load measurement.
Connect the feedback signal traces as close as possible to both ends of the sense
resistor. While the feedback traces do not handle high current, they are high
impedance and susceptible to interference from electrical and magnetic noise.
Avoid routing these traces near the power inductor and through vias.
• The sense resistor is to be placed as close to the inductor as possible, followed by
the first two bulk capacitors.
• The lead frame in the power MOSFETs is used to dissipate heat. To do this, each of
the power MOSFETs requires one square inch of copper.
• Avoid ground loops because they pick up noise. Use star or single point grounding.
The source of the lower synchronous bottom MOSFET is an ideal point where the
input and output ground planes may be connected.
• Keep the inductor-switching node small by placing the output inductor, switching
top MOSFET, and synchronous bottom MOSFET(s) close together on the same
copper fill.
• The MOSFET enable/gate traces to the driver must be as short (<1 in.), straight,
and wide as possible (20–25 mils). Ideally, the driver has to be placed right next to
the MOSFETs. Circuits using multiple top or bottom MOSFETs need to have
serpentine gate traces, so all the traces going to the top MOSFET gate(s) and
especially the bottom MOSFET gate(s) are the same length.
Figure 45. High Current Path With Bottom MOSFET(s) Turned ON
Voltage
Regulator
Control Circuitry
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