FSL116HR Fairchild Semiconductor, FSL116HR Datasheet - Page 9

• Manufacturer Part Number: FSL116HR
• Description: Power Switch ICs - POE / LAN Green Mode Fairchild Power Switch (FPS)
• Manufacturer: Fairchild Semiconductor

Specifications of FSL116HR

• Number Of Switches: Single
• On Resistance (max): 10 Ohms
• On Time (max): 10 ns
• Off Time (max): 14.9 ns
• Supply Voltage (max): 26 V
• Maximum Operating Temperature: + 105 C
• Minimum Operating Temperature: - 40 C
• Package / Case: DIP-8
• Maximum Power Dissipation: 1.5 W
• Mounting Style: Through Hole
• Operating Frequency: 100 KHz
• Switch Configuration: Single
• Switch Current (typ): 1.1 A
• Lead Free Status / Rohs Status: Details

© 2010 Fairchild Semiconductor Corporation
FSL116HR • Rev. 1.0.0
Functional Description
Startup
At startup, an internal high-voltage current source
supplies the internal bias and charges the external
capacitor (C
in Figure 14. When V
12V, the FPS™ begins switching and the internal high-
voltage current source is disabled. The FPS continues
normal switching operation and the power is provided
from the auxiliary transformer winding unless V
below the stop voltage of 8V.
Oscillator Block
The oscillator frequency is set internally and the FPS
has
Fluctuation of the switching frequency of a switched
power supply can reduce EMI by spreading the energy
over a wider frequency range than the bandwidth
measured by the EMI test equipment. The amount of
EMI reduction is directly related to the range of the
frequency variation. The range of frequency variation is
fixed internally; however, its selection is randomly
chosen by the combination of external feedback voltage
and internal free-running oscillator. This randomly
chosen switching frequency effectively spreads the EMI
noise nearby switching frequency and allows the use of
a cost-effective inductor instead of an AC input line filter
to satisfy the world-wide EMI requirements.
Figure 15. Frequency Fluctuation Waveform
a
random
A
) connected with the V
Figure 14. Startup Circuit
frequency
CC
reaches the start voltage of
fluctuation
CC
pin, as illustrated
function.
CC
goes
9
Feedback Control
FSL116HR employs Current-Mode control, as shown in
Figure 16. An opto-coupler (such as the FOD817A) and
shunt regulator (such as the KA431) are typically used
to implement the feedback network. Comparing the
feedback voltage with the voltage across the R
resistor makes it possible to control the switching duty
cycle. When the shunt regulator reference pin voltage
exceeds the internal reference voltage of 2.5V, the
opto-coupler LED current increases, the feedback
voltage V
reduced. This typically occurs when the input voltage is
increased or the output load is decreased.
Leading-Edge Blanking (LEB)
At the instant the internal SenseFET is turned on, the
primary-side capacitance and secondary-side rectifier
diode reverse recovery typically cause a high-current
spike through the SenseFET. Excessive voltage across
the R
operation in the Current-Mode PWM control. To counter
this effect, the FPS employs a leading-edge blanking
(LEB) circuit (see the Figure 16). This circuit inhibits the
PWM comparator for a short time (t
SenseFET is turned on.
Protection Circuits
The FPS has protective functions such as overload
protection (OLP), over-voltage protection (OVP), output-
short protection (OSP), under-voltage lockout (UVLO),
abnormal over-current protection (AOCP), and thermal
shutdown (TSD). Because these various protection
circuits are fully integrated in the IC without external
components, reliability is improved without increasing
cost. If a fault condition occurs, switching is terminated
and the SenseFET remains off. This causes V
When V
the protection is reset and the internal high-voltage
current source charges the V
pin. When V
(12V), the FPS resumes normal operation. In this
manner, the auto-restart can alternately enable and
disable the switching of the power SenseFET until the
fault condition is eliminated.
Figure 16. Pulse-Width-Modulation Circuit
SENSE
CC
FB
reaches the UVLO stop voltage, V
CC
is pulled down, and the duty cycle is
resistor leads to incorrect feedback
reaches the UVLO start voltage, V
CC
capacitor via the V
LEB
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) after the
STOP
CC
to fall.
SENSE
START
(8V),
STR