The FOD2742 Optically Isolated Ampliﬁer consists of the popular KA431 precision
programmable shunt reference and an optocoupler. The optocoupler is a gallium arsenide
(GaAs) 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-
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.
• 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
• VDE approval 136616
• CSA approval 1113643
• Low temperature coefﬁcient 50 ppm/°C max
• FOD2742A: tolerance 0.5%
FOD2742B: tolerance 1%
FOD2742C: tolerance 2%
• Power supplies regulation
• DC to DC converters
FUNCTIONAL BLOCK DIAGRAM
Pin function description
Error Ampliﬁer Compensation. This pin is the output of the error ampliﬁer. *
Voltage Feedback. This pin is the inverting input to the error ampliﬁer
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
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