FAN7621N Fairchild Semiconductor, FAN7621N Datasheet - Page 10

• Manufacturer Part Number: FAN7621N
• Description: IC CTRLR PROG OVP 16DIP
• Manufacturer: Fairchild Semiconductor

Specifications of FAN7621N

• Output Isolation: Isolated
• Frequency Range: 94 ~ 106kHz
• Power (watts): 1.56W
• Operating Temperature: -40°C ~ 130°C
• Package / Case: 16-DIP (0.300", 7.62mm)
• Product: Driver ICs - Various
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

© 2009 Fairchild Semiconductor Corporation
FAN7621 • Rev. 1.0.3
implemented by sweeping down the switching frequency
from an initial high frequency ( f
voltage is established. The soft-start circuit is made by
connecting R-C series network on the R
in Figure 19. FAN7621 also has an internal soft-start for
3ms to reduce the current overshoot during the initial
cycles, which adds 40kHz to the initial frequency of the
external soft-start circuit, as shown in Figure 20. The
initial frequency of the soft-start is given as:
It is typical to set the initial (soft-start) frequency of two ~
three times the resonant frequency ( f
network.
The soft-start time is three to four times the RC time
constant. The RC time constant is as follows:
4. Control Pin
The FAN7621 has a control pin for protection, cycle
skipping, and remote on/off. Figure 21 shows the internal
block diagram for control pin.
Protection : When the control pin voltage exceeds 5V,
protection
described in the protection section.
Pulse Skipping : FAN7621 stops switching when the
control pin voltage drops below 0.4V and resumes
switching when the control pin voltage rises above 0.6V.
To use pulse-skipping, the control pin should be
connected to the opto-coupler collector pin. The
frequency that causes pulse skipping is given as:
T
f
CON
SS
SKIP
ISS
=
f
Figure 20. Frequency Sweeping of Soft-Start
=
ISS
R
=
(
6
SS
f
Figure 21. Internal Block of Control Pin
s
5.2
R
⋅
5
LV
LV
R
OLP
OVP
C
min
23V
2 .
k
5V
min
CC
CC
is
SS
Ω
k
I
0.4 / 0.6V
OLP
+
40kHz
triggered.
+
+
-
+
-
5.2
. 4
-
+
R
R
16
SS
k
max
Ω
k
) 100 40 (
×
LV
x
Detailed
100
CC
good
+
(
kHz
I S S
Control loop
)
kHz
take over
) until the output
O
Auto-restart
applications
protection
) of the resonant
R
S
T
)
-Q
pin, as shown
Q
Stop Switching
time
are
(3)
(4)
(5)
10
Remote On / Off : When an auxiliary power supply is
used for standby, the main power stage using FAN7621
can be shut down by pulling down the control pin
voltage, as shown in Figure 23. R1 and C1 are used to
ensure soft-start when switching resumes.
5. Protection Circuits
The FAN7621 has several self-protective functions, such
as Overload Protection (OLP), Over-Current Protection
(OCP), Abnormal Over-Current Protection (AOCP),
Over-Voltage Protection (OVP), and Thermal Shutdown
(TSD). OLP, OCP, and OVP are auto-restart mode
protections; while AOCP and TSD are latch-mode
protections, as shown in Figure 24.
5.1
condition is detected, switching is terminated and the
MOSFETs remain off. When LV
voltage of 11.3V, the protection is reset. FAN7621
FAN7621
CON
R
R
T
max
Figure 22. Control Pin Configuration for
V
Auto-Restart Mode Protection : Once a fault
CC
Figure 23. Remote On / Off Circuit
R
min
R
min
OP1
C
R
SS
SS
Pulse Skipping
R1
C1
CON
RT
CS
CC
LV
falls to the LV
SG
CC
HV
CTR
HO
LO
CC
PG
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OP1
Main Off
CC
Output
Output
Aux
Main
stop