Diodes AP5004 Manuel d'utilisateur télécharger pdf (Page 9)

AP5004

PWM CONTROL 2.5A STEP-DOWN CONVERTER

AP5004

Document number: DS31444 Rev. 5 - 2

9 of 11

www.diodes.com

August 2010

Functional Description (Continued)

Output Capacitor Selection

An output capacitor is required to maintain the DC output voltage. Low ESR capacitors are preferred to keep the

output voltage ripple low. The characteristics of the output capacitor also affect the stability of the regulation

control system. The ESR dominates the impedance at the switching frequency.The output ripple is calculated as:

ESR

RIPPLE

≅

Output Rectifier Diode

The output rectifier diode supplies the current to the inductor when the high-side switch is OFF. To reduce losses

due to the diode forward voltage and recovery times, use a Schottky rectifier.

PCB Layout Guide

The dual Output pin (4) and VSS pins (7 & 8) on the SOP-8L package are internally connected to die pad. If low

& T

or a large PD (Power Dissipation) is needed, the PCB layout should allow for maximum possible copper

area exposure at the SW pins. Please also follow the steps below to reduce switching noise.

1. Connect C3 to VCC and VSS pin as closely as possible to get good power filter effect.

2. Connect ground side of the C2 & D1 as closely as possible.

Typical PC Board Layout:

Top Side Layout Guide

Bottom Side Layout Guide

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Diodes AP5004 Manuel d'utilisateur Page 9