FS6X1220RJ Fairchild Semiconductor, FS6X1220RJ Datasheet - Page 9

• Manufacturer Part Number: FS6X1220RJ
• Description: IC SWIT PWM CM OVP UVLO HV D2PAK
• Manufacturer: Fairchild Semiconductor

Specifications of FS6X1220RJ

• Output Isolation: Isolated
• Frequency Range: 270 ~ 330kHz
• Voltage - Input: 9 ~ 35 V
• Voltage - Output: 200V
• Power (watts): 36W
• Operating Temperature: -25°C ~ 150°C
• Package / Case: TO-263-7, D²Pak (6 leads + Tab), TO-263CB
• Number Of Outputs: 1
• Duty Cycle (max): 88 %
• Mounting Style: SMD/SMT
• Switching Frequency: 300 KHz
• Operating Supply Voltage: 35 V
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 25 C
• Synchronous Pin: No
• Topology: Flyback, Forward
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

FS6X0420RJ/ FS6X0720RJ/ FS6X1220RJ Rev. 1.0.1
Applications Information
1. Startup
To guarantee stable operation of the control IC, Vcc has under
voltage lockout (UVLO) with 6V hysteresis. Figure 16 shows the
relation between the supply current (Icc) and the supply voltage
(Vcc). Before Vcc reaches 15V, the start-up current is 60μA,
which is usually provided by the DC link through start-up resis-
tor. When Vcc reaches 15V, the control IC begins operation and
the operating current increases to 10mA as shown. Once the
control IC starts operation, it continues its normal operation
unless Vcc goes below the stop voltage of 9V.
Figure 16. Relation between Supply Current and
2. Feedback Control
The FS6X-Series employs current mode control. The voltage of
the feedback pin is compared with the current sense voltage for
pulse width modulation (PWM). Figure 17 illustrates the simpli-
fied PWM block. The feedback voltage determines the peak
drain current of the SenseFET. Usually, an opto-coupler, along
with the TL431(shunt regulator) are used to implement the feed-
back network. The collector of the opto-coupler transistor is
connected to the feedback pin and the emitter is connected to
the ground pin. When the voltage of the reference pin of the
TL431 exceeds the internal reference voltage of 2.5V, the opto-
coupler diode current increases, pulling down the feedback volt-
age.
Vo
Figure 17. Pulse Width Modulation (PWM) Cir-
10mA
60uA
Icc
431
Vfb
Cfb
Vstop=9V
FB
4
5uA
V
Vcc
SD
Voltage
D1
cuit
Vref
Vstart=15V
Vfb*
0.9mA
D2
28R
R
OSC
OLP
Driver
Gate
Vz
Vcc
9
3. Protection Circuit
Besides pulse-by-pulse current limit, the FS6X-Series has the
following self protection functions: over load protection (OLP),
over voltage protection (OVP), and thermal shutdown (TSD).
Because these protection circuits are fully integrated into the IC
without external components, the reliability is improved. In the
event of a fault condition, FS6X-Series enters into auto-restart
operation. Once the fault condition occurs, switching operation
is terminated, and the MOSFET remains off, which causes Vcc
to be reduced. When Vcc reaches 9V, the protection is reset
and the supply current reduces to 60uA. Then, Vcc begin to
increase with the current provided through the start-up resistor.
When Vcc reaches 15V, FS6X-Series resumes its normal oper-
ation if the fault condition is removed. In this manner, the auto-
restart alternately enables and disables the switching of the
power MOSFET until the fault condition is eliminated as illus-
trated in Figure 18.
3.1 Pulse-by-pulse Current Limit
As shown in Figure 17, the drain current of the power MOSFET
is limited by the inverting input of PWM comparator (Vfb*).
Assuming that the 0.9mA current source flows only through the
internal resistor (28R +R= 2.9k), the cathode voltage of diode
D2 is about 2.6V. Since D1 is blocked when the feedback volt-
age (Vfb) exceeds 2.6V, the maximum voltage of the cathode of
D2 is 2.6V. Therefore, the maximum value of Vfb* is about 0.1V,
which limits the peak value of the power MOSFET drain current.
Figure 18. Auto Restart Operation After Protec-
10mA
60uA
Vds
Vcc
15V
Icc
9V
Power
on
operation
Normal
occurs
Fault
tion
situation
Fault
removed
Fault
operation
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Normal
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