Datasheet

SN65HVD1050
SLLS632B –DECEMBER 2005–REVISED MARCH 2010 www.ti.com
APPLICATION INFORMATION
Thermal Shutdown
The SN65HVD1050 has a thermal shutdown feature that turns off the driver outputs when the junction
temperature nears 190°C. This shutdown prevents catastrophic failure from bus shorts, but does not protect the
circuit from possible damage. The user should strive to maintain recommended operating conditions and not
exceed absolute-maximum ratings at all times. If an SN65HVD1050 is subjected to many, or long-duration faults
that can put the device into thermal shutdown, it should be replaced.
Bus Loading
Q: How many HVD1050 nodes can be connected on a bus?
A: In the CAN standard ISO 11898-2 the driver differential output is specified with a 60Ω load (must be greater
than 1.5V) and with a fully-loaded bus (must be greater than 1.2V). The HVD1050 is specified to meet the 1.5V
requirement with a 60Ω load, and 1.4V with a 45Ω load. The differential input resistance of the HVD1050 is a
minimum of 30kΩ. If 167 transceivers are in parallel on a bus, this is equivalent to a 180Ω differential load. That
transceiver load of 180Ω in parallel with the 60Ω (two 120Ω termination resistors) gives a total 45Ω. Therefore,
the HVD1050 supports over 167 transceivers on a single bus segment, with margin to the 1.2V CAN
requirement.
Dominant Time-Out Feature
A dominant-time-out circuit in the SN65HVD1050 prevents the driver from blocking network communication in the
event of a hardware or software failure of the local CAN controller. The time-out circuit is triggered by a falling
edge on TXD (pin 1). If no rising edge is seen before the time-out constant of the circuit expires, the driver is
disabled. The circuit is then reset by the next rising edge on TXD. This feature prevents a faulty local CAN
controller from corrupting the entire network with a “stuck” dominant state. The dominant time-out timer is
selected to pass all normal CAN messages; however, non-standard applications may inadvertently trigger the
dominant time-out if long strings of dominant bits are attempted at slow data rates.
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