FAIRCHILD SEMICONDUCTOR FOD2742A FOD2742B FOD2742C User Manual (2)
Summary
Achieve high-efficiency power conversion with this single-package solution that uniquely combines an optocoupler, precision reference voltage source, and error amplifier. Delivering robust isolation up to 2,500V RMS, the FOD2742 series is essential for isolated AC to DC supplies and advanced DC/DC converters. It provides superior performance through low temperature coefficients and high functional integration, allowing power supply designers to significantly reduce component count and save valuable space in tightly packaged systems. This manual details electrical specifications, application guidelines, and configuration methods for achieving optimized system regulation.
Page 1 Text Content
OPTICALLY ISOLATED ERROR AMPLIFIER
FOD2742A FOD2742B FOD2742C
DESCRIPTION The FOD2742 Optically Isolated Amplifier consists of the popular KA431 precision programmable shunt reference and an optocoupler. The optocoupler is a gallium arsenide (Ga As) light emitting diode optically coupled to a silicon phototransistor. It comes in 3 grades of reference voltage tolerance = 2%, 1%, and 0.5%. The Current Transfer Ratio (CTR) ranges from 100% to 200%. It also has an outstanding temperature coefficient of 50 ppm/°C. It is primarily intended for use as the error amplifier/ reference voltage/optocoupler function in isolated ac to dc power supplies and dc/dc con- verters.
FUNCTIONAL BLOCK DIAGRAM
When using the FOD2742, power supply designers can reduce the component count and save space in tightly packaged designs. The tight tolerance reference eliminates the need for adjustments in many applications. The device comes in a 8-pin small outline package.
NC LED
FEATURES Optocoupler, precision reference and error amplifier in single package
2.5V reference CTR 100% to 200%
2,500V RMS isolation UL approval E90700, Volume 2 BSI approval 8661, 8662
NC GND
VDE approval 136616 CSA approval 1113643 Low temperature coefficient 50 ppm/°C max FOD2742A: tolerance 0.5% FOD2742B: tolerance 1% FOD2742C: tolerance 2%
APPLICATIONS Power supplies regulation DC to DC converters
PIN DEFINITIONS Pin Number Pin Name Pin function description
NC Not connected
Phototransistor Collector Phototransistor Emitter
NC Not connected GND Ground COMP Error Amplifier Compensation. This pin is the output of the error amplifier. * FB Voltage Feedback. This pin is the inverting input to the error amplifier LED Anode LED. This pin is the input to the light emitting diode.
* The compensation network must be attached between pins 6 and 7.
© 2003 Fairchild Semiconductor Corporation Page 1 of 13 12/9/04
Page Summary Contents For FAIRCHILD SEMICONDUCTOR FOD2742A FOD2742B FOD2742C User Manual (2)
Manual Details
| Brand | Fairchild |
|---|---|
| Pages | 14 |
| File Size | 167.35 KB |
| Published | May 31, 2026 |
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Frequently Asked Questions
What is the primary function of the FOD2742 series?
It operates as an error amplifier, reference voltage source, and optocoupler in a single package, primarily for isolated ac to dc power supplies.
What are the different tolerance options available?
The ROHS comes in three grades with tolerance levels of 2%, 1%, or 0.5% (FOD2742C, FOD2742B, and FOD2742A, respectively).
Where is the compensation network connected?
The compensation network must be attached between pins 6 (COMP) and 7 (FB).
Is there a required reflow temperature profile for soldering?
Yes, one time soldering reflow is recommended with a peak reflow temperature of 245°C.