HCPL-7720 Datasheet, PDF (15/18 Pages) Agilent(Hewlett-Packard) – 40 ns Propagation Delay CMOS Optocoupler

AC LINE
NODE/APP SPECIFIC
uP/CAN
HCPL
772x/072x
HCPL
772x/072x
TRANSCEIVER
NON ISO
5V
*HCPL
772x/072x
REG.
GALVANIC
ISOLATION
BOUNDARY
DRAIN/SHIELD
SIGNAL
POWER
NETWORK
POWER
SUPPLY
* OPTIONAL FOR BUS V + SENSE
V+ (SIGNAL)
V– (SIGNAL)
V+ (POWER)
V– (POWER)
Figure 19. Isolated node with transceiver powered by the network.
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.
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
DEVICENET NODE
NODE/APP SPECIFIC
uP/CAN
HCPL
772x/072x
HCPL
772x/072x
TRANSCEIVER
AC LINE
5 V REG.
5 V REG.
ISOLATED
SWITCHING
POWER
SUPPLY
GALVANIC
ISOLATION
BOUNDARY
DRAIN/SHIELD
SIGNAL
POWER
V+ (SIGNAL)
V– (SIGNAL)
V+ (POWER)
V– (POWER)
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
(V_DD1) 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
(V_O) go HIGH.
Figure 20. Isolated node providing power to the network.
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