FS7M0880YDTU Fairchild Semiconductor, FS7M0880YDTU Datasheet - Page 7

• Manufacturer Part Number: FS7M0880YDTU
• Description: IC SWIT PWM CM OVP UVLO HV TO3P
• Manufacturer: Fairchild Semiconductor

Specifications of FS7M0880YDTU

• Output Isolation: Isolated
• Frequency Range: 60 ~ 72kHz
• Voltage - Input: 9 ~ 30 V
• Voltage - Output: 800V
• Power (watts): 190W
• Operating Temperature: 25°C ~ 150°C
• Package / Case: TO-3P-5
• Power Switch Family: FS7M0880
• Input Voltage: -0.3 to 8.1V
• Power Switch On Resistance: 1.2Ohm
• Output Current: 6A
• Number Of Outputs: Single
• Mounting: Through Hole
• Supply Current: 8mA
• Package Type: TO-3P
• Operating Temperature (min): -25C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Commercial
• Pin Count: 5 +Tab
• Power Dissipation: 190W
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: FS7M0880YDTU_NL; FS7M0880YDTU_NL

to the SPS V
starts the protection circuit. Therefore, V
appropriately kept below 24V during normal operation.
OCP (Over Current Protection)
The FPS has various built-in, basic protection features. They
are the UVLO (Under Voltage Lock Out), OLP (Over Load
Protection) and OCP (Over Current Protection). However, if
a secondary side diode short or load short occur due to a
worst case condition, such as a maximum input voltage
putting a large strain on the device, another external
component may need to be added. By adding these
requirements in the FPS, superior reliability and
advantageous cost can be achieved.
When gate on signal of the SenseFet is received,
simultaneously the OCP block senses Ipeak through the
sense resistor for 1us. After the OCP block has turned on,
the voltage across the resistor is compared to the pre-set
voltage in the comparator, and, if it takes longer than 200ns
within the allowed comparison time of 1us, then the
comparator produces a high signal, which latches the OCP.
fig 4. shows the OCP latch waveform. When there is a diode
short/load short, the SPS turns on for the minimum turn-on
time. If the instantaneous current is of the form shown in fig
4., the OCP block opens a 1us window to compare the
voltage proportional to the current across the resistor with
the reference voltage and latches. Here, the 100ns delay
after the 200ns is the delay time to SenseFET gate off and is
generated from the comparison of the voltage across the
sense resistor.
Soft start operation
Normally, the SMPS output voltage increases from start up
with a fixed time constant. This is due to the capacitive
component of the load. At start up, therefore, the feedback
signal applied to the PWM comparator's inverting input
reaches its maximum value (1V), This is because the
feedback loop is effectively open. Also at this time, the
drain current is at its peak value (I
allowable power is being delivered to the secondary load.
With that said, note that when the SMPS pushes maximum
power to the secondary side for this initial fixed time, the
OCP Operating
OCP Operating
OCP Operating
OCP Operating
Minimum Turn-on Time
Minimum Turn-on Time
Minimum Turn-on Time
Minimum Turn-on Time
Fiqure 5. OCP Function & Block
CC
200ns
200ns
200ns
200ns
voltage. If V
100ns delay
100ns delay
100ns delay
100ns delay
CC
exceeds 24 V, the SPS IC
S
R
Q
C C C C
OCP time
OCP time
OCP time
OCP time
R R R R
peak
Latch signal
Latch signal
Latch signal
Latch signal
CC
) and maximum
should be
OCP Level
OCP Level
OCP Level
OCP Level
Rsense
Rsense
Rsense
Rsense
at the comparator’s inverting terminal no longer follows the
voltage across C
entire
circuit is seriously stressed. Use of a soft start function
avoids such stresses. Figure 6 shows how to implement a
soft start for a Fairchild Power Switch(FPS). At turn on, the
soft start capacitor on pin 5 of the Fairchild Power
Switch(FPS) starts to charge through the 1mA current
source. When the voltage across C
turns off. No more current flows to it from the 1mA current
source. Cs then continues to charge to 5V through the 20k
resistor.
Note that when the voltage across C
feedback signal. In shutdown or protection circuit operation,
capacitor C
restart.
10V
10V
10V
10V
4uA
4uA
4uA
4uA
S
#4
is discharged, to enable it to charge from 0V at
Figure 6. Soft Start Circuit.
0.9mA
0.9mA
0.9mA
0.9mA
S
. Instead, it follows the output voltage
CS
CS
CS
CS
#5
5V
20K
Fairchild Power
Fairchild Power
Fairchild Power
Fairchild Power
Switch(FPS)
Switch(FPS)
Switch(FPS)
Switch(FPS)
S
S
exceeds 3V, The voltage
reaches 3V, diode D
PWM
Comparator
FS7M0880
S
7