ISL8112 Intersil Corporation, ISL8112 Datasheet - Page 26

• Manufacturer Part Number: ISL8112
• Description: Main Power Supply Controllers
• Manufacturer: Intersil Corporation

• Ensure that the VSEN_ connection to COUT_ is short and
• Route high-speed switching nodes (BOOT_, UG_, PH_,
• Make all pin-strap control input connections (MODE,
Layout Procedure
Place the power components first with ground terminals
adjacent (Q2/Q4 source, CIN_, COUT_). If possible, make
all these connections on the top layer with wide, copper-filled
areas.
Mount the controller IC adjacent to the synchronous rectifier
MOSFETs close to the hottest spot, preferably on the back
side in order to keep UG_, GND, and the LG_ gate drive
lines short and wide. The LG_ gate trace must be short and
wide, measuring 50 mils to 100 mils wide if the MOSFET is
1” from the controller device.
Group the gate-drive components (BOOT_ capacitor, VIN
bypass capacitor) together near the controller device.
Make the DC/DC controller ground connections as follows:
1. Near the device, create a small analog ground plane.
2. Connect the small analog ground plane to GND and use
3. Create another small ground island for PGND and use
4. Connect the GND and PGND planes together at the
direct. However, in some cases it may be desirable to
deliberately introduce some trace length between the
VSEN_ connector node and the output filter capacitor (see
the Stability Considerations section).
and LG_) away from sensitive analog areas (VREF1,
ILIM_, and FB_). Use PGND1 and PGND2 as an EMI
shield to keep radiated switching noise away from the IC's
feedback divider and analog bypass capacitors.
ILIM_, etc.) to GND or VCC of the device.
the plane for the ground connection for the VREF1 and
VCC bypass capacitors, FB dividers and ILIM resistors (if
any).
the plane for the VIN bypass capacitor, placed very close
to the device.
metal tab under device.
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ISL8112
On the board's top side (power planes), make a star ground
to minimize crosstalk between the two sides. The top-side
star ground is a star connection of the input capacitors and
synchronous rectifiers. Keep the resistance low between the
star ground and the source of the synchronous rectifiers for
accurate current limit. Connect the top-side star ground
(used for MOSFET, input, and output capacitors) to the small
island with a single short, wide connection (preferably just a
via). Create PGND islands on the layer just below the
top-side layer (refer to the ISL8112 EV kit for an example) to
act as an EMI shield if multiple layers are available (highly
recommended). Connect each of these individually to the
star ground via, which connects the top side to the PGND
plane. Add one more solid ground plane under the device to
act as an additional shield, and also connect the solid
ground plane to the star ground via.
Connect the output power planes (VCORE and system
ground planes) directly to the output filter capacitor positive
and negative terminals with multiple vias.
November 21, 2006
FN6396.0