Broadcom

AV02-0876EN

19

HCPL-0720, HCPL-7720, HCPL-0721,

and HCPL-7721 Data Sheet

40-ns Propagation Delay, CMOS Optocoupler

Implementing PROFIBUS with the HCPL-772X/072X

An acronym for Process Fieldbus, PROFIBUS is essentially a twisted-pair serial link very similar to RS-485 capable of

achieving high-speed communication up to 12 MBd. As shown in Figure 18, a PROFIBUS Controller (PBC) establishes the

connection of a field automation unit (control or central processing station) or a field device to the transmission medium. The

PBC consists of the line transceiver, optical isolation, frame character transmitter/receiver (UART), and the FDL/APP

processor with the interface to the PROFIBUS user.

Figure 18: PROFIBUS Controller (PBC)

The recommended PROFIBUS application circuit is shown in Figure 19. 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 μF 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. The bypass capacitors are required because of the high-speed digital nature of the signals

inside the optocoupler.

Being very similar to multistation 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

essential in industrial communication interfaces.

PROFIBUS USER:

CONTROL STATION

(CENTRAL PROCESSING)

OR FIELD DEVICE

USER INTERFACE

FDL/APP

PROCESSOR

TRANSCEIVER

OPTICAL ISOLATION

UART

PBC

MEDIUM