ISO1050

SLLS983C – JUNE 2009 – REVISED JULY 2010

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APPLICATION INFORMATION

DOMINANT TIME-OUT

A dominant time-out circuit in the ISO1050 prevents the driver from blocking network communications if a local

controller fault occurs. The time-out circuit is triggered by a falling edge on TXD. If no rising edge occurs on TXD

before the time-out of the circuits expires, the driver is disabled to prevent the local node from continuously

transmitting a Dominant bit. If a rising edge occurs on TXD, commanding a Recessive bit, the timer will be reset

and the driver will be re-enabled. The time-out value is set so that normal CAN communication will not cause the

Dominant time-out circuit to expire.

FAILSAFE

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 spurious transitions due to an unstable supply. If Vcc1 is still active when this

occurs, the receiver output will go to a failsafe HIGH value in about 6 microseconds.

THERMAL SHUTDOWN

The ISO1050 has an internal thermal shutdown circuit that turns off the driver outputs when the internal

temperature becomes too high for normal operation. This shutdown circuit prevents catastrophic failure due to

short-circuit faults on the bus lines. If the device cools sufficiently after thermal shutdown, it will automatically

re-enable, and may again rise in temperature if the bus fault is still present. Prolonged operation with thermal

shutdown conditions may affect device reliability.

BUS LOADING

In the CAN standard ISO 11898-2 the driver differential output is specified with a 60

Ω load (must be greater than

1.5V) and with a fully-loaded bus (must be greater than 1.2V). The ISO1050 is specified to meet the 1.5V

requirement with a 60

Ω load, and 1.4V with a 45Ω load. The differential input resistance of the ISO1050 is a

minimum of 30K

Ω. If the 167 transceivers are in parallel on a bus, this is equivalent to a 180Ω differential load.

That transceiver load of 180

Ω in parallel with the 60Ω (two 120Ω termination resistors) gives a total 45Ω.

Therefore, the ISO1050 supports over 167 transceivers on a single bus segment, with margin to the 1.2V CAN

requirement.

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