FLS1600XS Datasheet, PDF (11/13 Pages) Fairchild Semiconductor – FLS-XS Series — Half-Bridge LLC Resonant Control IC for Lighting

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 the FPS™ is utilized.
5.4 Thermal Shutdown (TSD): Having the MOSFETs
and the control IC in one package makes it easier for
the control IC to detect the abnormal over-temperature
of the MOSFETs. If the temperature exceeds
approximately 130°C, thermal shutdown triggers.
6. Current Sensing Using a Resistor: FLS-XS 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 imbalance problems
may occur due to the radiated noise from the main
transformer, the inequality of the secondary side-leakage
inductances of main transformer, and so on. This is one
of the reasons that the control components in the vicinity
of RT pin are enclosed by the primary current flow 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
changes the turn-on duration of each MOSFET. 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
V_CS
CS
SG
PG
R_sense
Ids
Ns
I_ds
V_CS
Figure 23. Half-Wave Sensing
I_ds
Figure 25. Example for Duty Balancing
V_CS
Control
IC
V_CS
CS
Cr
Np
Ns
SG
PG
R_sense
Ns
Ids
Figure 24. Full-Wave Sensing
© 2010 Fairchild Semiconductor Corporation
FLS-XS Series • Rev.1.0.0
11
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