FSDM07652R Fairchild Semiconductor, FSDM07652R Datasheet - Page 13

• Manufacturer Part Number: FSDM07652R
• Description: SMPS Power Switch For LCD Monitors Flyback, (Green)The FSDM07652R is an Integrated Pulse Width Modulator (PWM) And Sense Fet Specifically Designed For High Performance Offline Switch Mode Power Supplies (SMPS) With Minimal External Components. This D
• Manufacturer: Fairchild Semiconductor

voltage may exceed the rated voltage before the over load
protection is activated, resulting in the breakdown of the
devices in the secondary side. In order to prevent this situa-
tion, an over voltage protection (OVP) circuit is employed.
In general, Vcc is proportional to the output voltage and the
FPS
voltage. If V
resulting in the termination of the switching operation. In
order to avoid undesired activation of OVP during normal
operation, Vcc should be designed to be below 19V.
3.4 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 150°C,
the thermal shutdown is activated.
4. Soft Start : The FPS
that increases PWM comparator inverting input voltage
together with the Sense FET current slowly after it starts up.
The typical soft start time is 10msec, The pulse width to the
power switching device is progressively increased to estab-
lish the correct working conditions for transformers, induc-
tors, and capacitors. The voltage on the output capacitors is
progressively increased with the intention of smoothly estab-
lishing the required output voltage. It also helps to prevent
transformer saturation and reduce the stress on the secondary
diode during startup.
5. Burst operation : In order to minimize power dissipation
in standby mode, the FPS
As the load decreases, the feedback voltage decreases. As
shown in figure 9, the device automatically enters burst
mode when the feedback voltage drops below
V
put voltages start to drop at a rate dependent on standby cur-
rent load. This causes the feedback voltage to rise. Once it
passes V
voltage then falls and the process repeats. Burst mode opera-
tion alternately enables and disables switching of the power
Sense FET thereby reducing switching loss in Standby
mode.
BURL
TM
uses Vcc instead of directly monitoring the output
(500mV). At this point switching stops and the out-
BURH
CC
(700mV) switching resumes. The feedback
exceeds 19V, an OVP circuit is activated
TM
TM
has an internal soft start circuit
enters burst mode operation.
Vds
V
0.5V
Ids
0.7V
Vo
Vo
FB
set
Figure 9. Waveforms of burst operation
T1
Switching
disabled
T2 T3
Switching
disabled
T4
FSDM07652R
time
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