ISL6314CRZ-T Datasheet, PDF (30/32 Pages) Intersil Corporation – Single-Phase Buck PWM Controller with Integrated MOSFET Drivers for Intel VR11 and AMD Applications

ISL6314
The power components should be placed first, which include
the MOSFETs, input and output capacitors, and the inductor.
Keep the gate drive traces short, resulting in low trace
impedances.
When placing the MOSFETs try to keep the source of the
upper FETs and the drain of the lower FETs as close as
thermally possible. Input Bulk capacitors should be placed
close to the drain of the upper FETs and the source of the lower
FETs. Locate the output inductor and output capacitors
between the MOSFETs and the load. The high-frequency input
and output decoupling capacitors (ceramic) should be placed
as close as practicable to the decoupling target, making use of
the shortest connection paths to any internal planes, such as
vias to GND next to, or on the capacitor solder pad.
The critical small components include the bypass capacitors
for VCC and PVCC, and many of the components
surrounding the controller including the feedback network
and current sense components. Locate the VCC and PVCC
bypass capacitors as close to the ISL6314 as possible. It is
especially important to locate the components associated
with the feedback circuit close to their respective controller
pins, since they belong to a high-impedance circuit loop,
sensitive to EMI pick-up.
A multi-layer printed circuit board is recommended. Figure 24
shows the connections of the critical components for the
converter. Note that capacitors C_xxIN and C_xxOUT could each
represent numerous physical capacitors. Dedicate one solid
layer, usually the one underneath the component side of the
board, for a ground plane and make all critical component
ground connections with vias to this layer.
Dedicate another solid layer as a power plane and break this
plane into smaller islands of common voltage levels. Keep the
metal runs from the PHASE terminal to output inductor short.
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 node. Use the remaining printed
circuit layers for small signal wiring.
Routing UGATE, LGATE, and PHASE Traces
Great attention should be paid to routing the UGATE, LGATE,
and PHASE traces since they drive the power train MOSFETs
using short, high current pulses. It is important to size them as
large and as short as possible to reduce their overall
impedance and inductance. They should be sized to carry at
least one ampere of current (0.02” to 0.05”). Going between
layers with vias should also be avoided, but if so, use two vias
for interconnection when possible.
Extra care should be given to the LGATE traces in particular
since keeping their impedance and inductance low helps to
significantly reduce the possibility of shoot-through. It is also
important to route each channels UGATE and PHASE traces
in as close proximity as possible to reduce their inductances.
Current Sense Component Placement and Trace
Routing
One of the most critical aspects of the ISL6314 regulator
layout is the placement of the inductor DCR current sense
components and traces. The R-C current sense components
must be placed as close to their respective ISEN+ and
ISEN- pins on the ISL6314 as possible.
The sense traces that connect the R-C sense components to
each side of the output inductors should be routed on the
bottom of the board, away from the noisy switching
components located on the top of the board. These traces
should be routed side by side, and they should be very thin
traces. It’s important to route these traces as far away from
any other noisy traces or planes as possible. These traces
should pick up as little noise as possible.
Thermal Management
For maximum thermal performance in high current, high
switching frequency applications, connecting the thermal
GND pad of the ISL6314 to the ground plane with multiple
vias is recommended. This heat spreading allows the part to
achieve its full thermal potential. It is also recommended
that the controller be placed in a direct path of airflow if
possible to help thermally manage the part.
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FN6455.2
October 8, 2009