FSCM0565R Fairchild Semiconductor, FSCM0565R Datasheet - Page 12

• Manufacturer Part Number: FSCM0565R
• Description: Green Mode Fairchild Power Switch Fps
• Manufacturer: Fairchild Semiconductor

3.3 Thermal Shutdown (TSD) : The Sense FET and the
control IC are built in one package. This makes it easy for
the control IC to detect the heat generation from the Sense
FET. When the temperature exceeds approximately 145 C,
the thermal protection is triggered resulting in shutdown of
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 9, the
frequency changes from 63KHz to 69KHz in 4ms.
5. Soft Start : The FSCM0565R has an internal soft start
circuit that increases PWM comparator inverting input
voltage together with the Sense FET current slowly after it
starts up. The typical soft start time is 15msec, 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. It also helps to prevent transformer saturation and
reduce the stress on the secondary diode during startup.
6. Burst operation : In order 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 10, the
69kHz
66kHz
63kHz
f
s
Drain current
Figure 9. Frequency Modulation
T
T
T
s
s
s
4ms
t
device automatically enters into burst mode when the
feedback voltage drops below V
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 V
resumes. The feedback voltage then falls and the process
repeats. Burst mode operation alternately enables and
disables switching of the power Sense FET thereby reducing
switching loss in standby mode.
Vds
V
0.3V
Ids
0.5V
Vo
Vo
FB
set
Figure 10. Waveforms of burst operation
T1
Switching
disabled
T2 T3
BL
BH
(300mV). At this point
Switching
disabled
(500mV) switching
T4
FSCM0565R
time
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