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 2004 Semtech Corp.

www.semtech.com

POWER MANAGEMENT

SC2688

Layout Guidelines (Cont.)

4) The Output Capacitor(s) (Cout) should be located as

close to the load as possible, fast transient load currents

are supplied by Cout only, and connections between Cout

and the load must be short, wide copper areas to mini-

mize inductance and resistance.

5) The SC2688 is best placed over a quiet ground plane

area, avoid pulse currents in the Cin, Q1, Q2 loop flowing

in this area. PGND should be returned to the ground plane

close to the package. The AGND pin should be connected

to the ground side of (one of) the output capacitor(s). If

this is not possible, the AGND pin may be connected to

the ground path between the Output Capacitor(s) and the

Cin, Q1, Q2 loop. Under no circumstances should AGND

be returned to a ground inside the Cin, Q1, Q2 loop.

6) Vcc for the SC2688 should be supplied from the 5V

supply through a 10

Ω resistor, the Vcc pin should be

decoupled directly to AGND by a 0.1

µF ceramic capacitor,

trace lengths should be as short as possible.

7) The Current Sense resistor and the divider across it

should form as small a loop as possible, the traces run-

ning back to CS+ and CS- on the SC2688 should run par-

allel and close to each other. The 0.1

µF capacitor should

be mounted as close to the CS+ and CS- pins as possible.

8) Ideally, the grounds for the two LDO sections should be

returned to the ground side of (one of) the output

capacitor(s).

Vout

5V

+

+

Currents in Power Section