FSFR1800USL Fairchild Semiconductor, FSFR1800USL Datasheet - Page 12

• Manufacturer Part Number: FSFR1800USL
• Description: Switching Converters, Regulators & Controllers 260W Powr Switch for Half Brdg Res Cnvtr
• Manufacturer: Fairchild Semiconductor

Specifications of FSFR1800USL

• Input Voltage: 5 V
• Switching Frequency: 300 KHz
• Operating Temperature Range: - 40 C to + 130 C
• Mounting Style: Through Hole
• Duty Cycle (max): 52 %
• Package / Case: SIP-9
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

© 2009 Fairchild Semiconductor Corporation
FSFR-US Series • Rev.1.0.2
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.
5.3 Over-Voltage Protection (OVP): When the LV
reaches 23V, OVP is triggered. This protection is used
when auxiliary winding of the transformer to supply V
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
approximately 130 ° C, the thermal shutdown triggers.
MOSFETs.
V
V
CS
CS
Figure 23. Half-Wave Sensing
Figure 24. Full-Wave Sensing
R
sense
CS
CS
Control
Control
SG
SG
IC
IC
Ids
If
Ids
PG
PG
the
R
Cr
sense
Cr
Np
V
I
V
Np
I
ds
temperature
ds
CS
CS
Ns
Ns
Ns
Ns
exceeds
CC
CC
12
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 R
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 R
each MOSFET different. It is strongly recommended to
separate the control components in the vicinity of R
from the primary current flow pattern on PCB layout.
Figure 25 shows an example for the duty-balanced case.
Figure 25. Example for Duty Balancing
T
pin, which makes the turn-on duration of
T
pin are enclosed by the
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T
pin