Avago Technologies ACPL-224-500E - Manual (Page 17)

AV02-4387EN 14 Avago Technologies
Digital Optoisolators:
An Overview
Figure 1. Photodiode/Transistor Optoisolator
Figure 2. Split Darlington Transistor Optoisolator
Introduction
Avago Technologies offers a wide
array of Optoisolators for noise
rejection, ground loop current
elimination, and high voltage
isolation for digital data trans-
mission and communication ap-
plications. The product offering
includes low speed (100 kbit/s to
1 M bit/s) split Darlington or single
transistor type optoisolators to high
speed 25 M bit/s cascaded amplifier
stage optoisolators with Schottky
transistor or CMOS output stage.
Description
Figure 1 shows a Photodiode/Transis-
tor Optoisolator where a PIN photo-
diode detector is coupled to a single
transistor amplifier output stage (e.g.
HCPL-4504). Compared to a typical
phototransistor optoisolator, a PIN
photodetector diode reduces the
base-collector “Miller” capacitance and
allows operability at a much higher
speed.
Figure 2 shows a Split Darlington
Output Stage, where an emitter-fol-
lower stage is added between a PIN
photodiode and the output ampli-
fier. This allows the optoisolator to be
driven at a much lower input drive
current, as low as 40 mA for the HCPL-
4701/HCPL-4731 family or 0.5 mA for
the 6N139 family. This allows much
higher current transfer ratio (CTR) or
current gain at the output, and TTL/
CMOS gates can be easily driven.
1
1
2
8
7
6
5
LED
V+
3
4
SHIELD
HCPL-4504
HCPL-0454
HCNW4504
PHOTO
DIODE
(PIN)
2
R IN
R L
V OUT
I F
TRANSISTOR
AMPLIFIER
V IN
1
1
2
8
7
6
5
LED
3
4
SHIELD
HCPL-0701
6N139/8
HCPL-4701/4731
PHOTO
DIODE
(PIN)
2
R 1
R L
V OUT
V CC
I F
SPLIT
DARLINGTON
AMPLIFIER
V IN