AN-3012 Datasheet, PDF (1/8 Pages) Fairchild Semiconductor – High Speed Logic Compatible

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Application Note AN-3012
High Speed Logic Compatible, Half-Pitch Mini-Flat
Optocoupler, FODM8061
Introduction
The FODM8061, a high-speed, high noise immunity
optocoupler, is constructed in a high insulation voltage SO5
mini-flat package. This optocoupler’s optical input uses an
aluminum gallium arsenide, AlGaAs, LED. The LED is
coupled to a high-speed bipolar integrated logic compatible
receiver. One major advantage of this product is that the high
speed optical IC is specified with guaranteed performance at
both 3.3V and 5V logic supplies. The optocoupler’s open
collector Schottky-clamped transistor output insures
compatibility with a wide range of logic families. The
optocoupler’s key AC and DC characteristics are guaranteed
over an operating temperature range of -40°C to +110°C.
This application note highlights the key electrical and
switching performances of the high speed optocoupler,
FODM8061. It also explores the data communication signal
quality by examining the eye diagrams and the optocoupler’s
common usage in logic interfacing applications.
The SO5 Mini-Flat Package Improves
PCB Layout
The FODM8061 optocoupler is an enhanced version of the
industry standard 6N137. The 6N137 optocoupler’s package
is an 8-pin dual in-line DIP leadform configuration. [Refer to
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
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
bidirectional data communication and logic interfacing.
This package utilizes Fairchild's patented “Optoplanar^®”
co-planar packaging technology. This packaging technology
enhances the superior common mode transient immunity of
the shielded optical integrated receiver.
This package has received Underwriter’s Laboratories
1577 (UL1577) safety approval for an insulation test voltage
(VISO) of 3,750Vac(RMS), and pending IEC60747-5-2
approval status. This mini-flat package is also compatible
with 260°C surface mount solder reflow assembly processes.
FODM8061’s Electrical Operation
The FODM8061 is a two chip optical hybrid. The input chip
is a high speed, low input current, infrared light emitting
diode, LED. The LED generates an optical flux in direct
relationship to the LED’s forward current, I_F. The LED’s
output is coupled to a high speed bipolar optical receiver
through a low capacitance, “co-planar” optical coupling. The
receiver IC converts the optical energy into electrical current
and amplifies it to drive a load.
Figure 1 shows the block diagram of the FODM8061
optocoupler. The input consists of the anode and cathode
of an IR LED. This LED has a typical forward voltage, V_F,
of 1.45V when the forward current, I_F, is 10mA. The photo
flux is coupled to a reverse-biased photodiode. The
photodiode generates a photocurrent which flows from its
anode into the bipolar amplifier. This linear amplifier has
a typical current gain of 60dB and a 40MHz bandwidth.
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
a bias and regulator circuit function. This circuit isolates the
photodiode from power supply, common mode noise that can
be coupled into the V_CC, and output of the optocoupler.
Anode 1
Bias & Regulator ^{6 V}CC
Cathode 3
Amp
5 V_O
4 GND
Figure 1. FODM8061 Block Diagram
This optocoupler functions as a logic inverter. A logic input
signal which forces a forward current greater than 5mA
through the LED will cause the output transistor to sink
current supplied by an external load. Table 1 illustrates the
truth table for positive logic.
Table 1. Truth Table
LED
Off
On
Output
High
Low
REV. 1.0 3/9/10