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

%XV ZRXOG EH ³VWXFN GRPLQDQW´ EORFNLQJ

communication for the whole network but

TXD DTO prevents this and frees the bus

for communication after the time tTXD_DTO.

tTXD_DTO

Communication from

repaired local node

Communication from other

network nodes

Figure 8-3. Example Timing Diagram for Devices With TXD DTO

8.3.3.2 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.

8.3.3.3 Undervoltage Lockout and Fail-Safe

The supply pins have undervoltage detection that places the device in protected or fail-safe mode. This protects

the bus during an undervoltage event on VCC1 or VCC2 supply pins. If the bus-side power supply VCC2 is

lower than about 4 V, 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 fail-safe HIGH (recessive) value in about 6 microseconds.

Table 8-1. Undervoltage Lockout and Fail-Safe

VCC1

VCC2

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 (Fail-Safe High)

space

Note

After an undervoltage condition is cleared and the supplies have returned to valid levels, the device

typically resumes normal operation in 300 µs

8.3.3.4 Floating Pins

Pullups and pulldowns should be used on critical pins to place the device into known states if the pins float. The

TXD pin should be pulled up through a resistor to VCC1 to force a recessive input level if the microprocessor

output to the pin floats.

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ISO1050

SLLS983L – JUNE 2009 – REVISED OCTOBER 2023

Copyright © 2023 Texas Instruments Incorporated

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