HCPL-0721 datasheet(15/18 Pages) HP

15 / 18 page

Figure 20. Isolated node providing power to the network.

Isolated Node Providing Power to

the Network

Figure 20 shows a node providing

power to the network. The AC line

powers a regulator which

provides five (5) volts locally. The

AC line also powers a 24 volt

isolated supply, which powers the

network, and another five-volt

regulator, which, in turn, powers

the transceiver and isolated

(network) side of the two

optocouplers. This method is

recommended when there are a

limited number of devices on the

network that don’t require much

power, thus eliminating the need

for separate power supplies.

More importantly, the unique

“dual-inverting” design of the

HCPL-772X/072X ensure the

network will not “lock-up” if

either AC line power to the node

is lost or the node powered-off.

Specifically, when input power

(VDD1) to the HCPL-772X/072X

located in the transmit path is

eliminated, a RECESSIVE bus

state is ensured as the

HCPL-772X/072X output voltage

(VO) go HIGH.

NODE/APP SPECIFIC

uP/CAN

HCPL

772x/072x

HCPL

772x/072x

TRANSCEIVER

5 V REG.

V+ (SIGNAL)

V– (SIGNAL)

V+ (POWER)

V– (POWER)

GALVANIC

ISOLATION

BOUNDARY

AC LINE

DRAIN/SHIELD

SIGNAL

POWER

ISOLATED

SWITCHING

POWER

SUPPLY

5 V REG.

DEVICENET NODE

Figure 19. Isolated node with transceiver powered by the network.

NODE/APP SPECIFIC

uP/CAN

HCPL

772x/072x

HCPL

772x/072x

TRANSCEIVER

NON ISO

5 V

REG.

NETWORK

POWER

SUPPLY

V+ (SIGNAL)

V– (SIGNAL)

V+ (POWER)

V– (POWER)

GALVANIC

ISOLATION

BOUNDARY

AC LINE

DRAIN/SHIELD

SIGNAL

POWER

*HCPL

772x/072x

* OPTIONAL FOR BUS V + SENSE

node with an un-powered isolated

Physical Layer will accumulate

errors and become bus-off if it

attempts to transmit. The Bus V+

sense signal would be used to

change the BOI attribute of the

DeviceNet Object to the “auto-

reset” (01) value. Refer to Volume

1, Section 5.5.3. This would cause

the node to continually reset until

bus power was detected. Once

power was detected, the BOI

attribute would be returned to the

“hold in bus-off” (00) value. The

BOI attribute should not be left in

the “auto-reset” (01) value since

this defeats the jabber protection

capability of the CAN error

confinement. Any inexpensive

low frequency optical isolator can

be used to implement this feature.

HCPL-0721 Datasheet(PDF) 15 Page - Agilent(Hewlett-Packard)

HCPL-0721 Datasheet(HTML) 15 Page - Agilent(Hewlett-Packard)

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