TCAN1042-Q1_17 Datasheet, PDF (17/40 Pages) Texas Instruments – Automotive Fault Protected CAN Transceiver with CAN FD

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TCAN1042-Q1, TCAN1042V-Q1, TCAN1042H-Q1
TCAN1042HV-Q1, TCAN1042G-Q1, TCAN1042GV-Q1
TCAN1042HG-Q1, TCAN1042HGV-Q1
SLLSES9B – FEBRUARY 2016 – REVISED MAY 2017
9.3 Feature Description
9.3.1 TXD Dominant Timeout (DTO)
During normal mode (the only mode where the CAN driver is active), the TXD DTO circuit prevents the
transceiver from blocking network communication in the event of a hardware or software failure where TXD is
held dominant longer than the timeout period t_{TXD_DTO}. The DTO circuit timer starts on a falling edge on TXD.
The DTO circuit disables the CAN bus driver if no rising edge is seen before the timeout period expires. This
frees the bus for communication between other nodes on the network. The CAN driver is re-activated when a
recessive signal is seen on the TXD terminal, thus clearing the TXD DTO condition. The receiver and RXD
terminal still reflect activity on the CAN bus, and the bus terminals are biased to the recessive level during a TXD
dominant timeout.
TXD
(driver)
TXD fault stuck dominant: example PCB
failure or bad software
t_{TXD_DTO}
Driver disabled freeing bus for other nodes
Fault is repaired & transmission
capability restored
Normal CAN
communication
CAN
Bus
Signal
t_{TXD_DTO}
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whole network but TXD DTO prevents this and frees the bus for
communication after the time t_{TXD_DTO}.
Communication from
other bus node(s)
Communication from
repaired node
RXD
(receiver)
Communication from
local node
Communication from
other bus node(s)
Communication from
repaired local node
Figure 12. Example Timing Diagram for TXD DTO
NOTE
The minimum dominant TXD time allowed by the TXD DTO circuit 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 immediately by an error frame. This, along with the t_{TXD_DTO}
minimum, limits the minimum data rate. Calculate the minimum transmitted data rate by:
Minimum Data Rate = 11 / t_{TXD_DTO}.
9.3.2 Thermal Shutdown (TSD)
If the junction temperature of the device exceeds the thermal shutdown threshold (T_TSD), the device turns off the
CAN driver circuits thus blocking the TXD-to-bus transmission path. The CAN bus terminals are biased to the
recessive level during a thermal shutdown, and the receiver-to-RXD path remains operational. The shutdown
condition is cleared when the junction temperature drops at least the thermal shutdown hysteresis temperature
(T_{TSD_HYS}) below the thermal shutdown temperature (T_TSD) of the device.
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