FS8S0765RCBYDTU_NL Fairchild Semiconductor, FS8S0765RCBYDTU_NL Datasheet - Page 13

• Manufacturer Part Number: FS8S0765RCBYDTU_NL
• Manufacturer: Fairchild Semiconductor

Specifications of FS8S0765RCBYDTU_NL

• Power Switch Family: FS8S0765RCB
• Input Voltage: -0.3 to 10V
• Power Switch On Resistance: 1.4Ohm
• Output Current: 7A
• Number Of Outputs: Single
• Mounting: Through Hole
• Supply Current: 9mA
• Package Type: TO-220F
• Operating Temperature (min): -25C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Commercial
• Pin Count: 5 +Tab
• Power Dissipation: 145W
• Lead Free Status / Rohs Status: Compliant

FS8S0765RCB Rev. 1.0.2
5. Synchronization: To reduce the effect of switching
noise on the screen, the SMPS for monitor synchronizes
its switching frequency to an external signal, typically the
horizontal sync flyback signal. The switching frequency
of the FPS can vary from 20 kHz to 150 kHz according to
the external sync signal. The internal sync comparator
detects the sync signal and determines the SenseFET
turn-on time. The SenseFET is turned on at the negative
edge of the sync comparator output. The reference volt-
age of the sync comparator is an inverted saw tooth with
a base frequency of 20kHz and a varying range between
5.8V and 7.2V, as shown in the Figure 29. The inverted
saw tooth reference gets rid of the excessive switching
noise at the first synchronized turn-on. The external sync
signal is recommended to have an amplitude higher than
4.2V.
6. Burst mode operation: To minimize the power
dissipation at standby mode, FS8S0765RCB has a burst
mode operation. In burst mode, the FPS reduces the
effective switching frequency and output voltage. The
FPS enters burst mode when the voltage of the soft start
pin is higher than 3V. No sync signal is applied and the
feedback voltage is lower than 1V. During the burst
mode operation, Vcc is hysteresis controlled between
11V and 12V. Once the FPS enters burst mode, it stops
switching operation until Vcc drops to 11V. When Vcc
reaches 11V, the FPS starts switching with switching
frequency of 40kHz and peak MOSFET current of 0.6A
until Vcc reaches 12V. When Vcc reaches 12V, the
switching operation is terminated again until Vcc reduces
to 11V. Figure 30 shows operating waveforms. The soft
start during the initial start-up is shown in the section 1.
During this period, there is no external sync signal and
the switching frequency is 20kHz. The section 2
represents the normal mode operation. The switching
frequency is synchronized with the external sync signal.
In the section 3, the external sync signal is removed;
however, the load still exists and the feedback voltage
(Vfb) is higher than 1V. In this period, the FPS does the
normal switching operation with switching frequency of
20kHz. The section 4 and 5 show the burst mode
Figure 29. The circuit for the synchronization
External
Sync
Rss
Css
Cfb
5
5
4
2μA
FS8S0765RCB
with external sync
Vref
0.9mA
D3
2.5R
R
7.2V
5.8V
SYNC COMP.
COMP.
PWM
OSC
DRIVER
GATE
Voffset
D
S
13
operation. At the end of the section 3, the load is
eliminated and the feedback voltage (Vfb) drops below
1V, forcing the FPS to stop switching operation. During
the section 4, Vcc goes down to 11V. During section 5,
Vcc is hysteresis controlled between 11V and 12V.
When the external sync signal is applied on the pin 5, the
FPS resumes normal operation. To minimize the power
consumption in standby mode, it is recommended to set
the value of Vcc during normal operation as high as
possible (about 29V).
15V
12V
11V
1V
Vcc
9V
5V
3V
Figure 30. The operation of the FS8S0765RCB
V
V
V
V
Vsync
at the normal mode and the off mode
Vfb
Vds
Vcc
Section I
Section 2
Section 3
Section 4
Section 5
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Section 6
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