Datasheet

TLE6251-3G
Fail Safe Features
Data Sheet 17 Rev. 1.1, 2011-06-06
7 Fail Safe Features
7.1 CAN Bus Failure Detection
The High Speed CAN Transceiver TLE6251-3G is equipped with a bus failure detection unit. In Normal Operation
mode the TLE6251-3G can detect the following bus failures:
• CANH shorted to GND
• CANL shorted to GND
• CANH shorted to
V
CC
• CANL shorted to V
CC
• CANH shorted to V
S
• CANL shorted to V
S
The TLE6251-3G can not detect the bus failures:
• CANH open
• CANL open
• CANH short to CANL
The TLE6251-3G detects the bus failures while sending a “Dominant” signal to the CAN bus. After sending four
“Dominant” bits to the CAN bus, a logical “Low” on the NERR pins indicates the CAN bus failure. For the failure
indication the “Dominant” bits require a minimum pulse width of 4 μs. In case the TLE6251-3G detects an CAN bus
failure, the failure is only indicated by the NERR pin, the transceiver doesn’t stop or block the communication, by
disabling the output stage for example.
Figure 9 CAN Bus Failure CANH short to
V
CC
1)
1) The communication on the CAN bus could still be possible even with a short CANH to V
CC
or CANH to V
S
. If the CAN bus
communication is possible or not, depends on parameters like the number of participants inside the CAN network, the
network termination, etc. This figure shows a working CAN bus communication as an example and it shall not be
considered as a liability that on HS CAN networks the CAN bus communication continues in every CAN bus failure case.
TxD
t
t
CANH
CANL
Short to V
CC
RxD
t
NERR
t
Four Dominant Bits