FSDM311A Fairchild Semiconductor, FSDM311A Datasheet - Page 9

• Manufacturer Part Number: FSDM311A
• Description: IC SWIT PWM GREEN OVP HV 8DIP
• Manufacturer: Fairchild Semiconductor

Specifications of FSDM311A

• Output Isolation: Isolated
• Frequency Range: 61 ~ 73kHz
• Voltage - Input: 7 ~ 20 V
• Voltage - Output: 650V
• Power (watts): 13W
• Operating Temperature: 25°C ~ 150°C
• Package / Case: 8-DIP (0.300", 7.62mm)
• On Resistance (max): 14 Ohms
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 25 C
• Maximum Power Dissipation: 1400 mW
• Mounting Style: Through Hole
• Supply Current: 1.5 mA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

© 2007 Fairchild Semiconductor Corporation
FSDM311A • Rev.1.0.2
4.1 Overload Protection (OLP): Overload is defined as
the load current exceeding a pre-set level due to an
unexpected event. In this situation, the protection circuit
should be activated to protect the SMPS. However,
even when the SMPS is operating normally, the
overload protection (OLP) circuit can be activated
during the load transition. To avoid this undesired
operation, the OLP circuit is designed to be activated
after a specified time to determine whether it is a
transient situation or an overload situation. If the output
consumes more than the maximum power determined
by I
rating voltage. This reduces the current through the
opto-coupler LED, which also reduces the opto-coupler
transistor current, thus increasing the feedback voltage
(V
blocked and the 5µA current source (I
charge C
increases until it reaches 4.5V, when the switching
operation is terminated, as shown in Figure 19. The
shutdown delay time is the time required to charge C
from 3V to 4.5V with 5µA current source.
4.2 Thermal Shutdown (TSD): The SenseFET and the
control IC are integrated, making it easier for the control
IC to detect the temperature of the SenseFET. When
the temperature exceeds approximately 145°C, thermal
shutdown is activated.
5. Soft-Start: The FPS has an internal soft-start circuit
that slowly increases the feedback voltage with the
SenseFET current right after it starts up. The typical
soft-start time is 15ms, as shown in Figure 20, where
progressive increment of the SenseFET current is
allowed during the start-up phase. The soft-start circuit
progressively increases current limits to establish
proper working conditions for transformers, inductors,
capacitors, and switching devices. It also helps to
prevent transformer saturation and reduces the stress
on the secondary diode.
4.5V
V
FB
3V
t
FB
12
). If V
LIM
=
C
, the output voltage (V
FB
Figure 19.
FB
V
FB
(
t
2
I
slowly up to V
exceeds 3V, the feedback input diode is
)
DELAY
t
1
−
V
(
t
1
)
;
t
12
= C
Overload Protection (OLP)
I
DELAY
Over Load Protection
FB
=
CC
(V(t
5
μ
. In this condition, V
O
2
A
) decreases below its
)-V(t
,
V
(
t
1
1
)) / I
)
=
3
DELAY
DELAY
V
,
V
(
) starts to
t
2
)
=
t
2
4
5 .
V
t
FB
FB
6. Burst Operation: To minimize the power dissipation
in standby mode, the FSDM311A enters burst mode
operation. As the load decreases, the feedback voltage
decreases. The device automatically enters burst mode
when the feedback voltage drops below V
At this point, switching stops and the output voltages
start to drop. This causes the feedback voltage to rise.
Once is passes V
The feedback voltage falls and the process repeats.
Burst mode operation alternately enables and disables
switching of the power MOSFET to reduce the switching
loss in standby mode.
9
0.55V
Vo
Vds
V
0.7V
Ids
Vo
FB
set
Figure 22.
Figure 21.
Figure 20.
BURH
Burst Operation Function
(0.70V), switching starts again.
Burst Operation Block
Internal Soft-Start
www.fairchildsemi.com
BURL
(0.55V).
t