SC2603EVB SEMTECH [Semtech Corporation], SC2603EVB Datasheet - Page 6

• Manufacturer Part Number: SC2603EVB
• Description: Simple PWM Boost Controller
• Manufacturer: SEMTECH [Semtech Corporation]

Layout Guidelines
Careful attention to layout requirements are necessary
for successful implementation of the SC2603 PWM con-
troller. High currents switching at 200kHz 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 Schottky ground.
2) The loop formed by the output Capacitor(s) (Cout), the
FET (Q1), the current sensing resistor, and the Schottky
(D1) must be kept as small as possible. This loop con-
tains all the high current, fast transition switching. Con-
nections should be as wide and as short as possible to
minimize loop inductance. Minimizing this loop area will
reduce EMI, lower ground injection currents, resulting in
electrically “cleaner” grounds for the rest of the system
and minimize source ringing, resulting in more reliable
gate switching signals.
3) The connection between the junction of Q1, D1 and
the output capacitor 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.
4) The Output Capacitor(s) (Cout) should be located as
close to the load as possible, fast transient load cur-
rents are supplied by Cout only, and connections be-
tween Cout and the load must be short, wide copper
areas to minimize inductance and resistance.
POWER MANAGEMENT
© 2005 Semtech Corp.
Applications Information
6
5) The SC2603 is best placed over an isolated ground
plane area. The soft-start capacitor, the V
capacitor, and the current sensing filter capacitor should
also connected to this ground pad area. This isolated
ground area should be connected to the main ground by
a trace that runs from the GND pin to the ground side of
the output capacitor. If this is not possible, the GND pin
may be connected to the ground path between the Out-
put Capacitor and the Cin, Q1, D1 loop. Under no cir-
cumstances should GND be returned to a ground inside
the Cin, Q1, D1 loop.
6) Input voltage of the SC2603 should be supplied from
the power rail through a 2.2~10Ω resistor, the V
should be decoupled directly to GND by a 0.1µF~1µf
ceramic capacitor, trace lengths should be as short as
possible.
7) An RC low pass filter is required to filter out leading
edge current spikes on the current sensing resistor. The
filter capacitor needs to be very close to the CS and
GND to reduce noise pickup.
SC2603
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IN
decoupling
IN
pin