AN-9752 Datasheet, PDF (1/6 Pages) Fairchild Semiconductor – Design Guidelines for New-Generation FPS™ FSB-Series

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AN-9752
Design Guidelines for New-Generation FPS™ FSB-Series
1. Introduction
The FSB-series is a next-generation Green-Mode Fairchild
Power Switch (FPS™) incorporating Fairchild’s innovative
mWSaver™ technology, which dramatically reduces
standby and no-load power consumption, enabling
conformance to worldwide standby efficiency guidelines. It
integrates advanced current-mode pulse-width modulator
(PWM) and an avalanche-rugged 700 V SenseFET in a
single package; allowing auxiliary power designs with
higher standby energy efficiency, reduced size, improved
reliability, and lower system cost than previous solutions.
The typical application circuit is shown in Figure 1.
This application note focuses on design consideration of
two unique functions of FSB-series: AX-CAP^® discharge
and adjustable peak current limit. It introduces AX-CAP^®
operation principle and provides the equations of discharge
time for worst-case scenarios. Then it shows how to achieve
the constant power limit and how to design the IPK pin
level for appropriate Over-Power Protection (OPP) level.
The design consideration for applying FSB-series to a
standby auxiliary power supply with single output is well
described in Fairchild application note AN-8024. It covers
designing the transformer, selecting the components,
feedback loop design, and design tips to maximize
efficiency. For multi-output applications, refer to Fairchild
application note AN-4137.
Figure 1. Typical Application Circuit
© 2011 Fairchild Semiconductor Corporation
Rev. 1.0.1 • 1/23/13
www.fairchildsemi.com