FAN5240 Datasheet, PDF (16/19 Pages) Fairchild Semiconductor – Multi-Phase PWM Controller for AMD Mobile Athlon TM and Duron TM

FAN5240
PRODUCT SPECIFICATION
Layout Considerations
Switching converters, even during normal operation,
produce short pulses of current which could cause substan-
tial ringing and be a source of EMI if layout constrains are
not observed.
There are two sets of critical components in a DC-DC
converter. The switching power components process large
amounts of energy at high rate and are noise generators.
The low power components responsible for bias and feed-
back functions are sensitive to noise.
A multi-layer printed circuit board is recommended.
Dedicate one solid layer for a ground plane. Dedicate
another solid layer as a power plane and break this plane
into smaller islands of common voltage levels.
Notice all the nodes that are subjected to high dV/dt voltage
swing such as SW, HDRV and LDRV, for example. All sur-
rounding circuitry will tend to couple the signals from these
nodes through stray capacitance. Do not oversize copper
traces connected to these nodes. Do not place traces con-
nected to the feedback components adjacent to these traces.
It is not recommended to use High Density Interconnect
Systems, or micro-vias on these signals. The use of blind or
buried vias should be limited to the low current signals only.
The use of normal thermal vias is left to the discretion of the
designer.
Keep the wiring traces from the IC to the MOSFET gate and
source as short as possible and capable of handling peak cur-
rents of 2A. Minimize the area within the gate-source path to
reduce stray inductance and eliminate parasitic ringing at the
gate.
Locate small critical components like the soft-start capacitor
and current sense resistors as close as possible to the respec-
tive pins of the IC.
The FAN5240 utilizes advanced packaging technology that
will have lead pitch of 0.6mm. High performance analog
semiconductors utilizing narrow lead spacing may require
special considerations in PWB design and manufacturing. It
is critical to maintain proper cleanliness of the area sur-
rounding these devices. It is not recommended to use any
type of rosin or acid core solder, or the use of flux in either
the manufacturing or touch up process as these may contrib-
ute to corrosion or enable electromigration and/or eddy cur-
rents near the sensitive low current signals. When chemicals
such as these are used on or near the PWB, it is suggested
that the entire PWB be cleaned and dried completely before
applying power.
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