FAIRCHILD AN-3012 User's Manual

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Application Note AN-3012 High Speed Logic Compatible, Half-Pitch Mini-Flat Optocoupler, FODM8061 Introduction FODM8061’s Electrical Operation The FODM8061, a high-speed, high noise immunity The FODM8061 is a two chip optical hybrid. The input chip optocoupler, is constructed in a high insulation voltage SO5 is a high speed, low input current, infrared light emitting mini-flat package. This optocoupler’s optical input uses an diode, LED. The LED generates an optical flux in direct aluminum gallium arsenide, Al Ga As, LED. The LED is relationship to the LED’s forward current, IF. The LED’s

coupled to a high-speed bipolar integrated logic compatible output is coupled to a high speed bipolar optical receiver receiver. One major advantage of this product is that the high through a low capacitance, “co-planar” optical coupling. The speed optical IC is specified with guaranteed performance at receiver IC converts the optical energy into electrical current both 3.3V and 5V logic supplies. The optocoupler’s open and amplifies it to drive a load.

collector Schottky-clamped transistor output insures

compatibility with a wide range of logic families. The Figure 1 shows the block diagram of the FODM8061 optocoupler’s key AC and DC characteristics are guaranteed optocoupler. The input consists of the anode and cathode over an operating temperature range of -40°C to +110°C. of an IR LED. This LED has a typical forward voltage, VF, of 1.45V when the forward current, IF, is 10m A. The photo This application note highlights the key electrical and flux is coupled to a reverse-biased photodiode. The switching performances of the high speed optocoupler, photodiode generates a photocurrent which flows from its FODM8061. It also explores the data communication signal anode into the bipolar amplifier. This linear amplifier has quality by examining the eye diagrams and the optocoupler’s a typical current gain of 60d B and a 40MHz bandwidth. common usage in logic interfacing applications. The output of this amplifier is a Schottky clamped open- collector NPN transistor. High levels of power supply and common mode power noise rejection is insured by including

The SO5 Mini-Flat Package Improves

a bias and regulator circuit function. This circuit isolates the

PCB Layout

photodiode from power supply, common mode noise that can

The FODM8061 optocoupler is an enhanced version of the be coupled into the VCC, and output of the optocoupler. industry standard 6N137. The 6N137 optocoupler’s package is an 8-pin dual in-line DIP leadform configuration. [Refer to

Bias & Regulator1Anode VCC

the Fairchild Semiconductor Optocoupler Selection Catalog for additional package selections.] The FODM8061’s smaller SO5 package results in a more condensed PCB footprint. This small footprint enhances multi-channel Amp VO packaging density without sacrificing channel-to-channel and input-to-output insulation safety. This is a primary consideration when isolation is needed for parallel and 4Cathode GND bidirectional data communication and logic interfacing.

This package utilizes Fairchild's patented “Optoplanar®” Figure 1. FODM8061 Block Diagram co-planar packaging technology. This packaging technology enhances the superior common mode transient immunity of This optocoupler functions as a logic inverter. A logic input the shielded optical integrated receiver. signal which forces a forward current greater than 5m A

through the LED will cause the output transistor to sink

This package has received Underwriter’s Laboratories current supplied by an external load. Table 1 illustrates the 1577 (UL1577) safety approval for an insulation test voltage truth table for positive logic. (VISO) of 3,750Vac(RMS), and pending IEC60747-5-2

approval status. This mini-flat package is also compatible Table 1. Truth Table

with 260°C surface mount solder reflow assembly processes.

LED Output Off High On Low

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