SN65HVD255

SN65HVD256

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SLLSEA2

– DECEMBER 2011

PROTECTION FEATURES

TXD DOMINANT TIME OUT (DTO)

During normal mode, the only mode where the CAN driver is active, the TXD dominant time out circuit prevents

the transceiver from blocking network communication in event of a hardware or software failure where TXD is

edge on TXD. If no rising edge is seen before the time out period of the circuit expires, the CAN bus driver is

disabled. This keeps the bus free for communication between other nodes on the network. The CAN driver is

re-activated when a recessive signal is seen on TXD pin, thus clearing the TXD dominant time out. The receiver

and RXD pin will still reflect the CAN bus and the bus pins will be biased to recessive level during a TXD

dominant time out.

APPLICATION NOTE: The minimum dominant TXD time allowed by the TXD dominant time out limits the

minimum possible transmitted data rate of the device. The CAN protocol allows a maximum of eleven

successive dominant bits (on TXD) for the worst case, where five successive dominant bits are followed

THERMAL SHUTDOWN

If the junction temperature of the device exceeds the thermal shut down threshold the device will turn off the

CAN driver circuits thus blocking the TXD to bus transmission path. The shutdown condition is cleared once the

junction temperature drops below the thermal shutdown temperature of the device.

APPLICATION NOTE: During thermal shutdown the CAN bus drivers will be turned off thus no transmission

is possible from TXD to the bus. The CAN bus pins will be biased to recessive level during a thermal

shutdown and the receiver to RXD path will remain operational.

UNDER VOLTAGE LOCKOUT

The supply pins have undervoltage detection which place the device in protected mode. This protects the bus

Table 4. Undervoltage Lockout 5V Only Device

DEVICE STATE

BUS OUTPUT

RXD

GOOD

Normal

Per Device State and TXD

Mirrors Bus

BAD

Protected

High Impedance

High Impedance (3-state)

DEVICE STATE

BUS OUTPUT

RXD

GOOD

GOOD

Normal

Per Device State and TXD

Mirrors Bus

BAD

GOOD

Protected

High Impedance

High (Recessive)

GOOD

BAD

Protected

Recessive

High Impedance (3-state)

BAD

BAD

Protected

High Impedance

High Impedance (3-state)

APPLICATION NOTE: Once an undervoltage condition is cleared and the supplies have returned to valid

levels the device will typically need 300

µs to transition to normal operation.

UNPOWERED DEVICE

The device is designed to be an "ideal passive" or

“no load” to the CAN bus if it is unpowered. The bus pins

(CANH, CANL) have extremely low leakage currents when the device is unpowered so they will not load down

the bus. This is critical if some nodes of the network will be unpowered while the rest of the of network remains in

operation. Logic pins will also have extremely low leakage currents when the device is unpowered so they will

not load down other circuits which may remain powered.

Copyright

© 2011, Texas Instruments Incorporated

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