Datasheet

Normal CAN
communication
CAN
Bus
Signal
TXD fault stuck dominant: example PCB failure or
bad software
Fault is repaired and local node
transmission capability restored
TXD
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communication for the whole network but
TXD DTO prevents this and frees the bus
for communication after the time t
TXD_DTO
.
t
TXD_DTO
Communication from
repaired local node
Communication from other
network nodes
TXD INPUT
CAN BUS OUTPUT
WITH TXD DTO
ISO1050
www.ti.com SLLS983H –JUNE 2009–REVISED JUNE 2013
Figure 3. Example Timing Diagram for Devices With TXD DTO
Thermal Shutdown
If the junction temperature of the device exceeds the thermal shut down threshold the device turns off the CAN
driver circuits thus blocking the TXD to bus transmission path. The shutdown condition is cleared when the
junction temperature drops below the thermal shutdown temperature of the device. If the fault condition is still
present, the temperature may rise again and the device would enter thermal shut down again. Prolonged
operation with thermal shutdown conditions may affect device reliability.
NOTE
During thermal shutdown the CAN bus drivers turn off; thus no transmission is possible
from TXD to the bus. The CAN bus pins are biased to recessive level during a thermal
shutdown, and the receiver to RXD path remains operational.
Undervoltage Lockout and Failsafe
The supply pins have undervoltage detection that places the device in protected or failsafe mode. This protects
the bus during an undervoltage event on V
CC1
or V
CC2
supply pins. If the bus-side power supply Vcc2 is lower
than about 2.7V, the power shutdown circuits in the ISO1050 will disable the transceiver to prevent false
transmissions due to an unstable supply. If Vcc1 is still active when this occurs, the receiver output (RXD) will go
to a failsafe HIGH (recessive) value in about 6 microseconds.
Table 3. Undervoltage Lockout and Failsafe
V
CC
1 V
CC
2 DEVICE STATE BUS OUTPUT RXD
GOOD GOOD Functional Per Device State and TXD Mirrors Bus
BAD GOOD Protected Recessive High Impedance (3-state)
GOOD BAD Protected High Impedance Recessive (Failsafe High)
NOTE
After an undervoltage condition is cleared and the supplies have returned to valid levels,
the device typically resumes normal operation in 300 µs
Floating Pins
Pull ups and pull downs should be used on critical pins to place the device into known states if the pins float. The
TXD pin should be pulled up via a resistor to V
CC1
to force a recessive input level if the microprocessor output to
the pin floats.
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