Power Supplies and Bypassing
The recommended PROFIBUS
application circuit is shown in
Figure 23. Since the HCPL-772X/
072X are fully compatible with
CMOS logic level signals, the
optocoupler is connected directly
to the transceiver. Two bypass
capacitors (with values between
0.01 and 0.1
µF)
are required and
should be located as close as
possible to the input and output
power-supply pins of the
HCPL-772X/072X. For each
capacitor, the total lead length
between both ends of the
capacitor and the power supply
pins should not exceed 20 mm.
The bypass capacitors are
required because of the high-
speed digital nature of the signals
inside the optocoupler.
Being very similar to multi-station
RS485 systems, the HCPL-061N
optocoupler provides a transmit
disable function which is
necessary to make the bus free
after each master/slave
transmission cycle. Specifically,
the HCPL-061N disables the
transmitter of the line driver by
putting it into a high state mode.
In addition, the HCPL-061N
switches the RX/TX driver IC into
the listen mode. The HCPL-061N
offers HCMOS compatibility and
the high CMR performance
(1 kV/µs at V
CM
= 1000 V)
essential in industrial
communication interfaces.
GALVANIC
ISOLATION
BOUNDARY
5V
8 V
DD2
0.01 µF
Rx
7
V
DD1
1
V
IN
2
3
0.01
µF
0.01
µF
4
3
5V
1 V
DD1
Tx
2 V
IN
0.01 µF
3
V
DD2
8
7
0.01
µF
ISO 5 V
D
DE
GND
5
0.01 µF
1M
1
R
ISO 5 V
ISO 5 V
HCPL-772x
6 V
O
HCPL-072x
5 GND
2
8
V
CC
A 6
+
RT
B
7
SHIELD
–
GND
1
4
SN75176B
2 RE
HCPL-772x
HCPL-072x
V
O
6
GND
2
5
4 GND
1
ISO 5 V
1
5V
2 ANODE
Tx ENABLE
1, 0 kΩ
3 CATHODE
4
V
E
7
0.01
µF
V
O
6
GND 5
680
Ω
V
CC
8
HCPL-061N
Figure 23. Recommended PROFIBUS application circuit.
17
AGILENT [ AGILENT TECHNOLOGIES, LTD. ]
