SG5842JA Fairchild Semiconductor, SG5842JA Datasheet - Page 4

• Manufacturer Part Number: SG5842JA
• Description: The highly integrated SG5842A/JA series of PWM controllers provides several features to enhance the performance of flyback converters
• Manufacturer: Fairchild Semiconductor

© 2007 Fairchild Semiconductor Corporation
SG5842A/SG582JA • Rev. 1.4.3
Pin Configuration
Pin Definitions
Pin #
1
2
3
4
5
6
7
8
SENSE
Name
GATE
GND
VDD
VIN
FB
RT
RI
Ground
The signal from the external compensation circuit is fed into this pin. The PWM duty cycle is
determined in response to the signal from this pin and the current-sense signal from Pin 6. If FB
voltage exceeds the threshold, the internal protection circuit disables PWM output after a
predetermined delay time.
For startup, this pin is pulled HIGH to the rectified line input via a resistor. Since the startup
current requirement is very small, a large startup resistance can be used to minimize power loss.
A resistor connected from the RI pin to GND provides a constant current source. This determines
the center PWM frequency. Increasing the resistance reduces PWM frequency. Using a 26KΩ
resistor results in a 65KHz center PWM frequency.
For over-temperature protection. An external NTC thermistor is connected from this pin to the
GND pin. The impedance of the NTC decreases at high temperatures. Once the voltage of the
RT pin drops below a fixed limit, PWM output is latched off.
Current sense. The sensed voltage is used for peak-current-mode control and cycle-by-cycle
current limiting.
Power supply. The internal protection circuit disables PWM output if V
The totem-pole output driver for the power MOSFET, which is internally clamped below 18V.
Figure 4. Pin Configuration
4
Description
DD
is over-voltage.
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