Avago Technologies ACPL-224-500E - Manual (Page 25)

AV02-4387EN 22 Avago Technologies
Description
The above schematic shows a very
simple RS-232C data communication
isolation interface using a 6N139 op-
tocoupler. This circuit operates with
an LED forward current of 0.5 mA
when the input is at 3 V. The 1N4150
diode protects the LED during nega-
tive signal voltages. Since a low
diode current is used to operate the
6N139, the twisted pair line can be
up to 120 m. However, the data rate
may have to be lowered to account
for slower charging and discharging
of the total line capacitance.
Performance of Circuit
• RS­232C link twisted pair cable
length: up to 120 m for low data
rates
• Typical optocoupler propaga tion
delay: 20 µs
Benefits
• Simple, low cost isolated interface
• Meets worldwide regulatory stan-
dards for isolation
Alternative Avago Parts
1) HCPL4701, 6N138/9, 4N45/6,
HCPL-2730/1 High-Gain, Low In-
put Current Optocoupler
2) HCPL-0700/1, HCPL-0730/1,
HCPL-M700/1 Small Outline
High-Gain, Low Input Current
Optocoupler
3) HCPL-270L/HCPL-070L 3.3V, 100
kBd Optocoupler
Data Communications Applications
Isolated RS-232C/E Interface
V
O
7
5
6
8
2
3
4
1
RS-232C
INPUT
(± 3 V TO ± 25 V)
3.3 k Ω
CMOS or LSTTL
6N139
CC
V
L
R
1N4150