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SC2603

POWER MANAGEMENT

Applications Information

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.

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 2.2~10

Ω 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.