SC2618 Semtech, SC2618 Datasheet - Page 7

• Manufacturer Part Number: SC2618
• Description: Miniature PWM Controller for Buck Regulator
• Manufacturer: Semtech

Careful attention to layout requirements are necessary
for successful implementation of the SC2618 controller.
High currents switching at up to 500kHz are present in
the application and their effect on ground plane voltage
differentials must be understood and minimized.
1). The high power parts of the circuit should be laid out
first. A ground plane should be used, the number and
position of ground plane interruptions should be such as
to not unnecessarily compromise ground plane integrity.
Isolated or semi-isolated areas of the ground plane may
be deliberately introduced to constrain ground currents
to particular areas, for example the input capacitor and
bottom FET ground.
2). The loop formed by the Input Capacitor(s) (Cin), the
Top FET (Q1) and the Bottom FET (Q2) must be kept as
small as possible. This loop contains all the high current,
fast transition switching. Connections should be as wide
and as short as possible to minimize loop inductance.
Minimizing this loop area will a) reduce EMI, b) lower
ground injection currents, resulting in electrically “cleaner”
POWER MANAGEMENT
Layout Guidelines
 2004 Semtech Corp.
VCC IN
0.1uF
10
VBST IN
5
3
2
U1
BST
VCC
GND
SC2618
10uF
DH
DL
FB
6
1
4
GND
Cin
7
grounds for the rest of the system and c) minimize source
ringing, resulting in more reliable gate switching signals.
Cin should consist of the bulk input capacitors and must
be supplemented with one or more ceramic decoupling
capacitors as close as possible to the FETs
3). The connection between the junction of Q1, Q2 and
the output inductor should be a wide trace or copper
region. It should be as short as practical. Since this con-
nection has fast voltage transitions, keeping this con-
nection short will minimize EMI. The connection between
the output inductor and the output capacitors should be
a wide trace or copper area, there are no fast voltage or
current transitions in this connection and length is not
so important, however adding unnecessary impedance
will reduce efficiency.
VPWR IN
Q1
Q2
L
Cout
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SC2618
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Vout