SC4624SETRT datasheet(16/20 Pages) SEMTECH

16 / 20 page

 2007 Semtech Corp.

www.semtech.com

POWER MANAGEMENT

SC4624

Operation

Application Information (Cont.)

Layout Guidelines

In order to achieve optimal thermal and noise immunity

for high frequency converters, special attention must be

paid to the PCB layout. The goal of layout optimization

is to minimize the high di/dt loops and reduce ground

bounce.

Output voltage setting, line regulation, stability , switching

frequency and OCP trip point shifted are affected by a

poor layout. The following guidelines should be used to

ensure proper functions of the converters.

Both Power ground (PGND) and signal ground (AGND)

are separated.

A ground plane is recommended to minimize noise

and copper losses, and maximize heat dissipation.

Start the PCB layout by placing the power components

first. Arrange the power circuit to achieve a clean

power flow route.

Minimize all high di/dt loops. These loops pass high

di/dt current. Make sure the trace width is wide

enough to reduce copper losses in this loop. Ground

bounce happen to magnetic flux changed and it is

proportional to a magnetic filed which goes through

high di/dt loops.

The input ceramic capacitor (C

IN) should be close to

IN pins and PGND pins.

Both input ceramic capacitor gnd and output ceramic

capacitor gnd are at same port.

A RC snubber circuit between PV

IN and PH pins is

helpful for stability operation. Be careful with power

derating of snubber circuit.

The V

CC bypass capacitor should be placed next to the

CC and AGND pins.

The OCP setting resistor (R

ISET) and filter capacitor

ISET) should be placed next to the ISET and AGND

pins.

Feedback divider connects to output connector by

Kelvin connection and far away from the noise sources

such as switching node and switching components.

A multilayer chip beads between AGND and PGND

will reduce the ground bounce injected to the “quiet”

circuit. It’s helpful for stability operation.

A large copper area underneath the SC4624 IC is

necessary for heat sinking purpose. And multiple

layers of large copper area connected through vias

can be used for better thermal performance. The size

of the vias as the connection between multiple layers

should not be too large or solder may seep through

10.

11.

12.

the big vias to the bottom layer during the re-flow process

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