ISL65426EVAL1Z Intersil, ISL65426EVAL1Z Datasheet - Page 21

• Manufacturer Part Number: ISL65426EVAL1Z
• Description: ISL65426 EVAL BOARD 1 - RoHS COMPLIANT - QFN
• Manufacturer: Intersil

ISL65426
Plane Allocation
PCB designers typically have a set number of planes
available for a converter design. Dedicate one solid layer,
usually an internal layer underneath the component side of
the board, for a ground plane and make all critical
component ground connections with vias to this layer.
One additional solid layer is dedicated as a power plane and
broken into smaller islands of common voltage. The power
plane should support the input power and output power
nodes. Use copper filled polygons on the top and bottom
circuit layers for the phase nodes. Use the remaining printed
circuit board layers for small signal wiring and additional
power or ground islands as required.
Signal Routing
If the output stage component placement guidelines are
followed, stray inductance in the switch current path is
minimized along with good routing techniques. Great
attention should be paid to routing the PHASE plane since
high current pulses are driven through them. Stray
inductance in this high-current path induce large noise
voltages that couple into sensitive circuitry. By keeping the
PHASE plane small, the magnitude of the potential spikes is
minimized. It is important to size traces from the LX pins to
the PHASE plane as large and short as possible to reduce
their overall impedance and inductance.
Sensitive signals should be routed on different layers or
some distance away from the PHASE plane on the same
layer. Crosstalk due to switching noise is reduced into these
lines by isolating the routing path away from the PHASE
plane. Layout the PHASE planes on one layer, usually the
top or bottom layer, and route the voltage feedback traces on
another layer remaining.
Thermal Management
For maximum thermal performance in high current, high
switching frequency applications, connecting the thermal
PGND pad of the ISL65426 to the ground plane with multiple
vias is recommended. This heat spreading allows the IC to
achieve its full thermal potential. If possible, place the
controller in a direct path of any available airflow to improve
thermal performance.
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FN6340.1
November 14, 2006