FS8S0765RCBYDTU_NL Fairchild Semiconductor, FS8S0765RCBYDTU_NL Datasheet - Page 12

• 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
7.5V
3.2 Overload Protection (OLP): When the load current
exceeds a preset level for longer than the pre-
determined time, protection circuit should be activated to
protect the SMPS. Because of the pulse-by-pulse
current limit capability, the maximum peak current
through the SMPS is limited, and the maximum input
power is restricted with a given input voltage. If the
output consumes beyond this maximum power, the
output voltage, together with primary side regulation
voltage, decrease below the set voltage. This reduces
the current through primary side regulation transistor,
which increases feedback voltage (Vfb). If Vfb exceeds
2.7V, D1 is blocked and the 2μA current source starts to
charge Cfb slowly, compared to when the 0.9mA current
source charges Cfb. In this condition, Vfb continues
increasing until it reaches 7.5V and the switching
operation is terminated at that time, as shown in Figure
27. The delay time for shutdown is the time required to
charge Cfb from 2.7V to 7.5V with 2μA.
15V
22V
Figure 26. The waveforms at the OLP and auto
9V
V
V
V
7.5V
2.7V
V
FB
Vds
Vcc
Figure 27. Overload protection
Vfb
T
1
Overload protection
T
12
= Cfb*(7.5-2.7)/I
restart
delay
Overload protection
Auto restart
T
2
t
time
time
time
12
3.3 Over Voltage Protection (OVP): In case of
malfunction in the primary side feedback circuit or
feedback loop open caused by a defect of solder, the
current through primary side control transistor becomes
almost zero. Then, Vfb climbs up in a similar manner to
the overload situation, forcing the preset maximum
current to be supplied to the secondary side until the
over load protection is activated. Because more energy
than required is provided to the output, the output
voltage may exceed the rated voltage before the over
load protection is activated, resulting in the breakdown of
the devices in the secondary side. To prevent this
situation, an over-voltage protection (OVP) circuit is
employed. When the Vcc voltage touches 37V, the OVP
block is activated.
3.4 Thermal Shutdown (TSD): The SenseFET and the
control IC are built in one package. This allows the
control IC to detect the heat generation from the
SenseFET. If the temperature exceeds approximately
160°C, the thermal shutdown is activated.
4. Soft Start: Figure 28 shows the soft-start circuit.
During the initial start up, the 0.9 mA current source
leaks out through Css and Rss. As Css is charged, the
leakage current decreases. By choosing much bigger
Css than Cfb, it is possible to increase the feedback
voltage slowly, forcing the SenseFET current to increase
slowly. After Css reaches its steady state value, D3 is
blocked and the soft switching circuit is decoupled from
the feedback circuit. If the value of Css is too large, there
is possibility that Vfb increases to 7.5V, activating the
over load protection during soft start time. To avoid this
situation, it is recommended that the value of Css should
not exceed 100 times the Cfb.
Css
Rss
Cfb
Figure 28. The circuit for the soft start
5
4
FS8S0765RCB
2μA
0.9mA
Vref
D3
50K
2.5R
R
COMP.
PWM
OSC
DRIVER
GATE
Voffset
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