ISL6310 Datasheet, PDF (25/27 Pages) Intersil Corporation – Two-Phase Buck PWM Controller with High Current Integrated MOSFET Drivers

ISL6310
layout of the critical components, and short, wide circuit
traces minimize the magnitude of voltage spikes.
There are two sets of critical components in a DC/DC
converter using a ISL6310 controller. The power-
components are the most critical because they switch large
amounts of energy. Next are small signal components that
connect to sensitive nodes or supply critical bypassing
current and signal coupling.
It is important to have a symmetrical layout, preferably with
the controller equidistantly located from the two power trains it
controls. Equally important are the gate drive lines (UGATE,
LGATE, PHASE): 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. Extra care should be given to the
LGATE traces in particular since keeping the impedance and
inductance of these traces helps to significantly reduce the
possibility of shoot-through. Equidistant placement of the
controller to the two power trains also helps keeping these
traces equally short (equal impedances, resulting in similar
driving of both sets of MOSFETs).
The power components should be placed first. Locate the input
capacitors close to the power switches. Minimize the length of
the connections between the input capacitors, C_IN, and the
power switches. Locate the output inductors and output
capacitors between the MOSFETs and the load. Locate the
high-frequency decoupling capacitors (ceramic) as close as
practicable to the decoupling target, making use of the shortest
connection paths to any internal planes, such as vias to GND
immediately next, or even onto the capacitor solder pad.
The critical small components include the bypass capacitors
for VCC and PVCC. Locate the bypass capacitors, CBP,
close to the device. 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. It is also
important to place current sense components close to their
respective pins on the ISL6310, including the RISEN
resistors, RS, RCOMP, CCOMP. For proper current sharing
route two separate symmetrical as possible traces from the
corresponding phase node for each RISEN.
A multi-layer printed circuit board is recommended. Figure 27
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 inductor L_OUT 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 nodes. Use the remaining printed circuit layers for
small signal wiring. The wiring traces from the IC to the
MOSFETs’ gates and sources should be sized to carry at least
one ampere of current (0.02” to 0.05”).
25
FN9209.4
August 7, 2008