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FSCM0565RJ Datasheet(PDF) 12 Page - Fairchild Semiconductor

Part No. FSCM0565RJ
Description  Green Mode Fairchild Power Switch (FPS)
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Maker  FAIRCHILD [Fairchild Semiconductor]
Homepage  http://www.fairchildsemi.com
Logo FAIRCHILD - Fairchild Semiconductor

FSCM0565RJ Datasheet(HTML) 12 Page - Fairchild Semiconductor

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FSCM0565R
12
control IC are built in one package. This makes it easy for
the control IC to detect the heat generation from the
SenseFET. When the temperature exceeds approximately
145
°C, the thermal protection is triggered resulting in
shutdown of the FPS.
4.
Frequency
Modulation:
EMI
reduction
can
be
accomplished by modulating the switching frequency of a
switched power supply. Frequency modulation can reduce
EMI by spreading the energy over a wider frequency range
than the band width measured by the EMI test equipment.
The amount of EMI reduction is directly related to the depth
of the reference frequency. As can be seen in Figure 21, the
frequency changes from 63KHz to 69KHz in 4ms.
Figure 21. Frequency Modulation
5. Soft Start: The FSCM0565R has an internal soft start
circuit that increases PWM comparator inverting input
voltage together with the SenseFET current slowly after it
starts up. The typical soft start time is15ms. The pulse width
to the power switching device is progressively increased to
establish the correct working conditions for transformers,
rectifier diodes and capacitors. The voltage on the output
capacitors is progressively increased with the intention of
smoothly
establishing
the
required
output
voltage.
Preventing transformer saturation and reducing stress on the
secondary diode during start up is also helpful.
6. Burst Operation: To minimize power dissipation in
standby mode, the FSCM0565R enters into burst mode
operation at light load condition. As the load decreases, the
feedback voltage decreases. As shown in Figure 22, the
device automatically enters into burst mode when the
feedback voltage drops below VBL (300mV). At this point
switching stops and the output voltages start to drop at a rate
dependent on standby current load. This causes the feedback
voltage to rise. Once it passes VBH (500mV), switching
resumes. The feedback voltage then falls, and the process
repeats. Burst mode operation alternately enables and
disables switching of the power SenseFET, thereby reducing
switching loss in standby mode.
Figure 22. Waveforms of Burst Operation
T
s
T
s
T
s
D rain Current
f
s
66kHz
69kHz
63kHz
4ms
t
V
FB
Vds
0.3V
0.5V
Ids
Vo
Voset
time
Switching
disabled
T1
T2 T3
Switching
disabled
T4


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