APW7120
Application Information (Cont.)
Layout Considerations (Cont.)
5. Use an dedicated trace to connect the ROCSET
and the Drain padof the low-side MOSFET, Kevin
connection , for accurate current sensing.
finally combined using ground plane construction or
single point grounding. Figure 2 illustrates the layout,
with bold lines indicating high current paths.
Components along the bold lines should be placed
close together. Below is a checklist for your layout:
6. Keep the switching nodes (UGATE, LGATE and
PHASE) away from sensitive small signal nodes
since these nodesare fast moving signals. Therefore
keep traces to these nodes as short as possible.
1. Begin the layout by placing thepower components
first. Orient the power circuitry to chieve a clean
power flowpath. If possible make all the connections
on one side of the PCB with wide, copper filled
areas.
7. Place thedecoupling ceramic capacitor CHF near
the Drain of the high-side MOSFET as close as
possible. The bulk capacitors CIN are also placed
near the Drain.
2. Connect the ground of feedback divider directly
to the GND pin of the IC using a dedicated ground
trace.
8. Place the Source of the high-side MOSFET and
theDrainof thelow-sideMOSFETasclosepossible.
Minimizing the impedance with wide layout plane
between the two padsreduces the voltage bounce
of the node.
3. The VCC decoupling capacitor should be right
next to the VCC and GND pins. Capacitor CBOOT
should be connected as close to the BOOT and
PHASE pins as possible.
9. Use a wide power ground plane, with low
impedance, to connects the CHF, CIN, COUT
,
Schottky diode and the Source of the low-side
MOSFETtoprovidealowimpedancepathbetween
the components for large and high frequency
switching currents.
4. Minimize the length and increase the width of
the trace between UGATE/LGATE and the gates
of the MOSFETs to reduce the impedance driving
the MOSFETs.
V
IN
CHF
C
IN
5
VCC
+
1
BOOT
4
LGATE
APW7120
U
2
8
COUT
Q1
UGATE
Q2
1
+
PHASE
L1
VOUT
Figure 2 Recommended Layout Diagram
Copyright ã ANPEC Electronics Corp.
Rev. A.4 - Jan., 2006
16
www.anpec.com.tw
ANPEC [ ANPEC ELECTRONICS COROPRATION ]
