FSQ500L Fairchild Semiconductor, FSQ500L Datasheet - Page 9

• Manufacturer Part Number: FSQ500L
• Description: IC SWIT PWM GREEN UVLO SOT223
• Manufacturer: Fairchild Semiconductor

Specifications of FSQ500L

• Output Isolation: Isolated
• Frequency Range: 120 ~ 140kHz
• Voltage - Input: 5 ~ 10 V
• Voltage - Output: 700V
• Power (watts): 3W
• Operating Temperature: -40°C ~ 125°C
• Package / Case: TO-261-4, TO-261AA, SOT-223-4
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

© 2008 Fairchild Semiconductor Corporation
FSQ500L • Rev. 1.0.1
3.1 Overload Protection (OLP): Overload is defined as
the load current exceeding its normal level due to an
unexpected abnormal event. In this situation, the
protection circuit should trigger to protect the SMPS.
However, even when the SMPS is in the normal
operation, the overload protection circuit can be
triggered during the load transition. To avoid this
undesired operation, the overload protection circuit is
designed to trigger after a specified time to determine
whether the situation is transient or a true overload.
Because of the pulse-by-pulse current limit capability,
the maximum peak current through the senseFET is
limited and, therefore, the maximum input power is
restricted with a given input voltage. If the output
consumes more than this maximum power, the output
voltage (V
reduces the current through the opto-coupler LED,
which also reduces the opto-coupler transistor current,
thus increasing the feedback voltage (V
exceeds 2.7V, D1 is blocked and the 5µA current
source starts to charge C
condition, V
4.5V, when the switching operation is terminated, as
shown in Figure 18. The delay time for shutdown is the
time required to charge C
In general, a 10 ~ 50ms delay time is typical for most
applications. This protection is implemented in auto
restart mode.
3.2 Thermal Shutdown (TSD): The senseFET and the
control IC in one package makes it easy for the control
IC to detect an abnormal over temperature of the
senseFET.
approximately 140°C, the thermal shutdown triggers.
When TSD triggers, delay current is disabled, switching
operation stops, and
voltage current source is set to 5.7V from 6.5V, as
shown in Figure 19. Since TSD signal prohibits the
senseFET from switching, there is no switching until the
junction temperature decreases sufficiently. If the
junction temperature is lower than 60°C typically, TSD
signal is removed and
V
makes the senseFET turn on and off with no voltage
and/or current stress.
4.5V
2.7V
CC
V
FB
increases from 5.7V to 6.5V, the soft-start function
O
Figure 18. Overload Protection
) decreases below the set voltage. This
FB
T
When
1
continues increasing until it reaches
Overload protection
T
12
V
V
the
= C
CC
CC
B
B
from 2.7V to 4.5V with 5µA.
B
is set to 6.5V again. While
through the internal high-
*(4.5-2.7)/I
slowly up to V
temperature
DELAY
FB
CC
). If V
. In this
exceeds
T
2
t
FB
9
4. Soft-Start: The soft-start time is tuned by an external
V
non-inverting input voltage together with the senseFET
current slowly after it starts up. Before V
V
I
reaches V
the
Therefore, C
makes the increasing slope of V
V
start block in Figure 2), and then V
of one of the input terminals of the PWM comparator.
The drain current follows V
because of the low-dominant feature of the PWM
comparator. The soft-start time can be made long or
short by selecting C
t
t
The peak value of the drain current of the power
switching device is progressively increased to establish
the
inductors, 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
stress on the secondary diode during startup.
6.5V
CH
S/S
S/S
5.7V
6.5V
6.0V
V
V
CC
START
CC
DS
CC
6V
5V
, I
Figure 19. Over-Temperature Protection (OTP)
is around 4.6ms with 27µF of C
t
and I
is shifted by 6.0V negatively (it is performed in soft-
1
capacitor (C
DELAY
=C
current
correct
, C
Power
V
A
on
CC
×6V/(I
A
START
START
is disabled to avoid unwanted OLP. Typically,
is charged by the current I
operation
Figure 20. Soft-Start Function
Normal
A
CH
consuming
working
is charged by the current I
, all internal blocks are activated, so that
are described in Figure 15. After V
-I
A
START
occurs
), which increases PWM comparator
TSD
A
, as described in Figure 20. During
)
t
1
conditions
t
S/S
t
S/S
CC
inside
t
=C
situation
2
Fault
-6.0V instead of the V
A
×0.5V/(I
CC
A
.
CC
IC
removed
for
become sluggish.
TSD
-6.0V is an input
CH
CH
becomes
-I
-I
transformers,
OP
www.fairchildsemi.com
CH
START
CC
)
-I
operation
OP
Normal
V
V
V
reaches
, where
CCREG
, which
START
STOP
t
I
OP
FB
CC
t
*
.