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SS6341

A multi-layer printed circuit board is recommended.

Figure 10 shows

the

connections

of

the

critical

each represent numerous physical capacitors. Dedicate

one solid layer for a ground plane and make all critical

component ground connections with vias to this layer.

PWM Output Capacitors

The load transient for the microprocessor core requires

high quality capacitors to supply the high slew rate (di/dt)

current demand.

The ESR (equivalent series resistance) and ESL

(equivalent series inductance) parameters determine the

buck capacitor values, rather than actual capacitance.

For a given transient load magnitude, the output voltage

transient change due to the output capacitor can be found

from the following equation:

∆

∆

∆

∆

V

ESR

I

ESL

I

T

OUT

OUT

OUT

=

×

+

×

where

+

+

+

Q1

GATE3

Q2

Css

SS

GATE2

PGND

LGATE

PHASE

UGATE

OCSET

VIN2

GND

VCC

+12V

+

+

Q3

Power Plane Layer

Circuit Plane Layer

Via Connection to Ground Plane

+

Q4

Fig. 10 Printed circuit board power planes and islands

Rev.2.01 6/26/2003