FSFR1800USL Fairchild Semiconductor, FSFR1800USL Datasheet - Page 11

• 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
It is typical to set the initial frequency of soft-start two to
three times the resonant frequency (f
network.
The soft-start time is three to four times of the RC time
constant. The RC time constant is as follows:
4. Self Auto-Restart: The FSFR-US series can restart
automatically even though any built-in protections are
triggered with external supply voltage. As can be seen in
Figure 20 and Figure 21, once any protections are
triggered, M1 switch turns on and V-I converter is
disabled. C
C
turns off, and V-I converter resumes at the same time.
The FSFR-US starts switching again with soft-start. If the
protections occur while V
level, the switching is terminated immediately, V
continues to increase until reaching V
discharged by M1.
After protections trigger, FSFR-US is disabled during the
stop-time, t
V
t
τ
STOP
CssL
SS
=
R
drops to V
Figure 19. Frequency Sweeping of Soft-Start
. The stop-time of FSFR-US can be estimated as:
SS
=
•
C
C
Figure 20. Internal Block of AR Pin
SS
SS
SS
stop
•
, where V
starts to be discharged until V
{
CssL
(
R
SS
. Then, all protections are reset, M1
=
R
MIN
Css
Css
)
decreases and reaches to
||
is under V
5
k
Ω
}
O
) of the resonant
CssH
CssL
, then C
Css
and V
across
SS
CssH
(4)
(5)
Css
is
11
For the soft-start time, t
5. Protection Circuits: The FSFR-US series has several
self-protective functions, such as Over-Current Protection
(OCP), Abnormal Over-Current Protection (AOCP), Over-
Voltage Protection (OVP), and Thermal Shutdown (TSD).
These protections are auto-restart mode protections as
shown in Figure 22.
Once a fault condition is detected, switching is terminated
and the MOSFETs remain off. When LV
stop voltage of 10V or AR signal is HIGH, the protection is
reset. The FSFR-US resumes normal operation when
LV
L V
5.1 Over-Current Protection (OCP): When the
sensing pin voltage drops below -0.58V, OCP is
triggered and the MOSFETs remain off. This protection
has a shutdown time delay of 1.5µs to prevent
premature shutdown during startup.
5.2 Abnormal Over-Current Protection (AOCP): If
the secondary rectifier diodes are shorted, large
current with extremely high di/dt can flow through the
MOSFET before OCP is triggered. AOCP is triggered
without shutdown delay when the sensing pin voltage
drops below -0.9V.
CC
V
CC
AR
I
Cr
reaches the start voltage of 12.5V.
Figure 21. Self Auto-Restart Operation
(a ) P r o te ction s a r e tr igge r e d, ( b ) F S F R- U S r e sta r ts
(a )
Figure 22. Protection Blocks
t
stop
(b )
t
S /S
s/s
it can be set as Equation (4).
( a)
(b )
CC
(a )
falls to the LV
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(b )
V
V
C ssH
C ssL
CC