FAN7528N Fairchild Semiconductor, FAN7528N Datasheet - Page 14

• Manufacturer Part Number: FAN7528N
• Description: IC PFC CTRLR CRM/TRANSITION 8DIP
• Manufacturer: Fairchild Semiconductor

Specifications of FAN7528N

• Mode: Critical Conduction (CRM), Discontinuous (Transition)
• Current - Startup: 40µA
• Voltage - Supply: 12 V ~ 23 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Through Hole
• Package / Case: 8-DIP (0.300", 7.62mm)
• Maximum Operating Temperature: + 125 C
• Mounting Style: Through Hole
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Frequency - Switching: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

FAN7528 Rev. 1.0.6
© 2005 Fairchild Semiconductor Corporation
3. Sawtooth Generator Block
The output of the error amplifier and the output of the
sawtooth generator are compared to determine the
MOSFET turn-off instance. The slope of the sawtooth is
determined by an external resistor connected to the
MOT pin. The voltage of the MOT pin is 1V and the slope
is proportional to the current flowing out of the MOT pin.
The internal ramp signal has 1V offset; therefore, the
drive output is shut down if the voltage of the COMP pin
is lower than 1V. The MOSFET on-time is maximum
when the COMP pin voltage is 5V. According to the slope
of the internal ramp, the maximum on-time can be pro-
grammed. The necessary maximum on-time depends on
the boost inductor, lowest AC line voltage, and maximum
output power. The resistor value should be designed
properly.
Figure 37. Sawtooth Generator Block
MOT
3
1V
Generator
Sawtooth
Error Amp
Output
1V
FAN7528 Rev. 1.00
Off Signal
14
4. Over-Current Protection Block
The MOSFET current is sensed using an external sens-
ing resistor for the over-current protection. If the CS pin
voltage is higher than 0.8V, the over-current protection
comparator generates a protection signal. An internal RC
filter is included to filter switching noise.
5. Switch Drive Block
The FAN7528 contains a single totem-pole output stage
designed for a direct drive of power MOSFET. The drive
output is capable of up to 400mA peak current with a typ-
ical rise and fall time of 50ns with 1nF load. The output
voltage is clamped to be 13V to protect MOSFET gate
even if the V
6. Under-Voltage Lockout Block
If the V
are enabled and start operation. If the V
below 8.5V, most of the internal blocks are disabled to
reduce the operating current. V
higher than 8.5V under normal conditions.
CS
Figure 38. Over-Current Protection Block
CC
4
voltage reaches 12V, the IC’s internal blocks
CC
40k
voltage is higher than 13V.
8pF
0.8V
Over-Current
Comparator
Protection
CC
FAN7528 Rev. 1.00
voltage should be
CC
Signal
voltage drops
OCP
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