FSDM311A Fairchild Semiconductor, FSDM311A Datasheet - Page 8

• 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
Functional Description
1. Start-up: At start-up, the internal high-voltage current
source supplies the internal bias and charges the
external V
V
internal high-voltage current source stops charging the
capacitor. The device is in normal operation provided
V
supplied from the auxiliary transformer winding.
Calculating the V
design with the FSDM311A. At initial start-up, the
maximum value of start operating current I
100µA, which supplies current to UVLO and V
blocks. The charging current I
equal to I
voltage, only the bias winding supplies V
the device. When the bias winding voltage is not
sufficient, the V
voltage and the internal current source is activated
again to charge the V
fluctuation (charging/discharging), the V
should be chosen for a value between 10µF and 47µF.
CC
CC
Figure 16. Charging V
does not drop below 7V. After start-up, the bias is
reaches 9V, the device starts switching and the
STR
CC
Figure 15.
– 100µA. After V
capacitor, as shown in Figure 15. When
CC
CC
level decreases to the UVLO stop
capacitor is an important step in
CC
Internal Start-up Circuit
capacitor. To prevent this V
CC
Capacitor through V
CC
Vcc
reaches the UVLO start
of the V
CC
START
CC
CC
capacitor is
current to
capacitor
is about
STR
REF
CC
2. Feedback Control: The FSDM311A is the voltage-
mode controlled device, as shown in Figure 17. Usually,
an opto-coupler and shunt regulator, such as KA431,
are used to implement the feedback network. The
feedback voltage is compared with an internally
generated sawtooth waveform that directly controls the
duty cycle. When the shunt regulator reference pin
voltage exceeds the internal reference voltage of 2.5V,
the opto-coupler LED current increases, the feedback
voltage V
cycle. This happens when the input voltage increases or
the output load decreases.
3. Leading-Edge Blanking (LEB): At the instant the
internal SenseFET is turned on, the primary-side
capacitance and secondary-side rectifier diode reverse
recovery typically cause a high-current spike through
the SenseFET. Excessive voltage across the R
resistor leads to incorrect pulse-by-pulse current limit
protection. To avoid this, a leading-edge blanking (LEB)
circuit disables pulse-by-pulse current limit protection
block for a fixed time (t
4. Protection Circuit: The FSDM311A has several
protective functions, such as overload protection (OLP),
over-voltage protection (OVP), under-voltage lockout
(UVLO), and thermal shutdown (TSD). Because these
protection circuits are fully integrated in the IC without
external components, the reliability is improved without
increasing costs. Once a fault condition occurs,
switching is terminated and the SenseFET remains off,
which causes V
stop voltage, V
internal high-voltage current source charges the Vcc
capacitor via the Vstr pin. When V
start voltage, V
operation. In this manner, the auto-restart can
alternately enable and disable the switching of the
power SenseFET until the fault condition is eliminated.
8
Figure 17.
FB
is pulled down, and it reduces the duty
Figure 18. Protection Block
STOP
CC
START
to fall. When V
(7V), the protection is reset and the
(9V), the device resumes normal
PWM and Feedback Circuit
LEB
) after the SenseFET turns on.
CC
CC
reaches the UVLO
reaches the UVLO
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SENSE