describe

The FOD2743 opto-isolated amplifier consists of the popular KA431 precision programmable shunt reference and optocoupler. An optocoupler is a light-emitting diode that optically couples gallium arsenide (gaas) to a silicon phototransistor. 1/3 reference voltage tolerance classes = 2%, 1% and 0.5%. The current transfer ratio (CTR) is between 50% and 100 %. It also has an outstanding temperature coefficient of 50 ppm/°C. Mainly used as error amplifier/isolated AC/DC power supplies and reference voltage/optocoupler functions in DC/DC converters. When using the FOD2743, power supply designers can reduce component count and save space in compact package designs. Tight tolerance benchmarks eliminate adjustments used in many applications. The device comes in an 8-pin dipped white package.

feature

Single package optocoupler, precision reference and error amplifier 2.5V reference voltage 50% to 100% current at 1 mA 5000V rms isolation UL Listed E90700, Volume 2 CSA Listed 1296837VDE Approval Pending BSI Approval Pending Low Temperature Coefficient 50 ppm max /℃FOD2743A: Tolerance 0.5% FOD2743B: Tolerance 1% FOD2743C: Tolerance 2%

Application: Power Management DC-DC Converters

FoD2643FOD2743 is an optically isolated error amplifier. It contains the three most common elements to make an isolated power supply, a voltage reference, an error amplifier and an optocoupler. Functionally equivalent to the popular ka431 shunt regulator plus cny17f-x optocoupler. Powering the Secondary Side The LED pins in the FOD2743 power the secondary side and in particular provide the current to run the LEDs. The structure of the actual FOD2743 specifies that it can be applied to the LED pins: the error amplifier output has a minimum reference voltage, and the LEDs are connected in series. Therefore, the minimum voltage applied to the LED pins is 2.5V+1.2V=3.7V. This voltage can be generated directly from the output of the inverter, or from a driven secondary winding. The secondary winding doesn't affect regulation because the input to the FB pin can still get bent from the output. The LED pins need to be powered through a current limiting resistor. The resistor value sets the amount of current that passes through, so must be combined with careful selection of the LED primary resistor selection. The output voltage of the feedback converter is selected by a resistor divider from the regulated output to the FB pin. This FOD2743 is trying to adjust its FB pin to the reference voltage, 2.5V. Therefore, the ratio of the two resistors should be: The absolute value of the top resistor is set by the input offset current at 5.2 microamps. To achieve 0.5% accuracy, the resistor RTOP should be: Compensation The compensation pin of the FOD2743 provides the designer with a design converter. The compensation network can be placed on the compressor pin and the FB pin. In a typical low bandwidth system, a 0.1µf capacitor can be used. For the more stringent requirements of the converter, the network should be designed based on measurements of the system loop. An excellent reference for this process can be found in "The Practical Design of Power Supplies," by Ron Lenk, IEEE Press, 1998. The secondary ground ground pins should be connected to the converter. No connection pins NC pins are not internally connected. They There should not be any connections to the secondary side as this could destroy the isolation structure.

phototransistor

The phototransistor is the output of the FOD2743. Under normal conditions the configuration collector will be connected to the pull-up resistor transmitter ground. Base connection is not required. The values of the pull-up resistors and the current-limiting resistors powering the LEDs must be carefully chosen to take into account the voltage range accepted by the PWM IC, as well as the current transfer ratio (CTR) of the optoisolator itself. Example: The voltage supplying the LED pin is +12V, the supply voltage for the collector pull-up is +10V, and the PWM IC is a Fairchild Fan4803 with a 5V reference. If we choose a 10KΩ resistor for the LED, the maximum current the LED can see is (12V-4V)/10KΩ = 800 microamps. The opto-isolator minimum is 50%, so the smallest collector diode draws 400 microamps of current to the phototransistor when fully energized. So the collector resistor must: choose 20kΩ to allow some margin. Marble------400µg or Rcollector<12.5k8486; The absolute value of the top resistor is set by the input offset The current is 5.2µA. To achieve 0.5% accuracy, the resistance RTOP should be: RTP—>1040 microamps.