FSFR1800USL 查看數據表（PDF） - Fairchild Semiconductor
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FSFR1800USL Datasheet PDF : 15 Pages
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5.3 Over-Voltage Protection (OVP): When the LVCC
reaches 23V, OVP is triggered. This protection is used
when auxiliary winding of the transformer to supply VCC
to FPS is utilized.
5.4 Thermal Shutdown (TSD): The MOSFETs and
the control IC in one package makes it easy for the
control IC to detect the abnormal over-temperature of
the MOSFETs. If the temperature exceeds
approximately 130°C, the thermal shutdown triggers.
6. Current Sensing Using Resistor: FSFR-US series
senses drain current as a negative voltage, as shown in
Figure 23 and Figure 24. Half-wave sensing allows low
power dissipation in the sensing resistor, while full-wave
sensing has less switching noise in the sensing signal.
Cr
7. PCB Layout Guidelines: Duty unbalance problems
may occur due to the radiated noise from main
transformer, the inequality of the secondary side leakage
inductances of main transformer, and so on. Among
them, it is one of the dominant reasons that the control
components in the vicinity of RT pin are enclosed by the
primary current flows pattern on PCB layout. The
direction of the magnetic field on the components caused
by the primary current flow is changed when the high-and
low-side MOSFET turn on by turns. The magnetic fields
with opposite directions induce a current through, into, or
out of the RT pin, which makes the turn-on duration of
each MOSFET different. It is strongly recommended to
separate the control components in the vicinity of RT pin
from the primary current flow pattern on PCB layout.
Figure 25 shows an example for the duty-balanced case.
Np
Ns
Control
IC
VCS
CS
SG
PG
Rsense
Ids
Ns
Ids
VCS
Figure 23. Half-Wave Sensing
Ids
Figure 25. Example for Duty Balancing
VCS
Control
IC
VCS
CS
Cr
Np
Ns
SG
PG
Rsense
Ns
Ids
Figure 24. Full-Wave Sensing
© 2009 Fairchild Semiconductor Corporation
FSFR-US Series • Rev.1.0.2
12
www.fairchildsemi.com
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