HCPL-0721 datasheet(17/18 Pages) HP

17 / 18 page

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.

Figure 23. Recommended PROFIBUS application circuit.

VDD2

GND2

VDD1

VIN

GND1

HCPL-772x

HCPL-072x

VDD1

VIN

GND1

VDD2

GND2

HCPL-772x

HCPL-072x

5 V

0.01 µF

0.01

µF

0.01

µF

SN75176B

VCC

GND

0.01

µF

ISO 5 V

1 M

0.01 µF

–

GALVANIC

ISOLATION

BOUNDARY

5 V

ISO 5 V

ANODE

VCC

GND

5 V

0.01

µF

ISO 5 V

Tx ENABLE

CATHODE

680

Ω

HCPL-061N

1, 0 k

Ω

SHIELD

HCPL-0721 Datasheet(PDF) 17 Page - Agilent(Hewlett-Packard)

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