TLE6252G Datasheet, PDF (9/25 Pages) Siemens Semiconductor Group – Fault Tolerant Differential CAN Transceiver

TLE 6252 G
Bus Failure Management
The TLE 6252 detects the bus failures as described in the following (Table 3, failures
listed according to ISO 11519-2) and automatically switches to a dedicated CANH or
CANL single wire mode to maintain data transmission if necessary. Therefore, it is
equipped with one differential receiver and 4 single ended comparators, two for each bus
line. To avoid false triggering by external RF influences the single wire modes are
activated after a certain delay time. As soon as the bus failure disappears the transceiver
switches back to differential mode after another time delay. Bus failures are indicated in
the normal operation mode by setting the NERR output to LOW.
To reduce EMI the dynamic slopes of the CANL and CANH signals are both limited and
symmetric. This allows the use of an unshielded twisted or parallel pair of wires for the
bus. During single-wire transmission the EMI performance of the system is degraded
from the differential mode.
The differential receiver threshold is set to – 2.8 V. This ensures correct reception in the
normal operation mode as well as in the failure cases 1, 2 and 4 with a noise margin as
high as possible. For these failures, further failure management is not necessary.
Detection of the failure cases 1, 2 and 4 is only possible when the bus is dominant.
Nevertheless, they are reported on the NERR output until transmission of the next CAN
word on the bus begins.
When one of the bus failures 3, 5, 6, 6a and 7 is detected, the defective bus wire is
disabled by switching off the affected bus termination and the respective output stage. A
wake-up from sleep mode via the bus is possible either via a dominant CANH or CANL
line. This ensures that a wake-up is possible even if one of the failures 1 to 7 occurs.
In case the transmission data input, TxD from the CAN controller is permanently
dominant, both, the CANH and CANL transmitting stage, are deactivated after a delay
time. This is necessary to prevent blocking the bus by a defective protocol unit. The
transmit time out error is flagged on NERR.
Semiconductor Group
9
1998-11-01