TLE6251-2G Datasheet, PDF (19/35 Pages) Infineon Technologies AG – High Speed CAN-Transceiver with Wake and Failure Detection

TLE6251-2G
Fail Safe Features
7.2.2 TxD to RxD Short Circuit Feature
A short between the pins TxD and RxD causes permanent blocking of the CAN bus. In the case, that the low side
driver capability of the RxD output pin is stronger as the high side driver capability of the external microcontroller
output, which is connected to the TxD pin of the TLE6251-2G, the RxD output signal overrides the TxD signal
provided by the microcontroller. In this case a continuous “Dominant” signal blocks the CAN bus. The TLE6251-
2G detects the short between the TxD and the RxD pin, disables the output driver stage and sets the internal local
failure flag. In Receive - Only Mode the TLE6251-2G indicates the TxD to RxD short by a logical “Low” signal on
the NERR pin. The TLE6251-2G releases the failure flag and the output driver stage by an operation mode change
from Receive - Only Mode to Normal Operation Mode.
7.2.3 RxD Permanent Recessive Clamping
A logical “High” signal on the RxD pin indicates the external microcontroller, that there is no CAN message on the
CAN bus. The microcontroller can transmit a message to the CAN bus only if the bus is recessive. In case the
logical “High” signal on the RxD pin is caused by a failure, like a short from RxD to V_IO, the RxD signal doesn’t
mirror the signal on the CAN bus. This allows the microcontroller to place a message to the CAN bus at any time
and corrupts CAN bus messages on the bus. The TLE6251-2G detects a permanent logical “High” signal on the
RxD pin and set the local error flag. In order to avoid any data collisions on the CAN bus the output driver stage
gets disabled. In Receive - Only Mode the TLE6251-2G indicates the RxD Clamping by a logical “Low” signal on
the NERR pin. The TLE6251-2G releases the failure flag and the output driver stage by a operation mode change
or if the RxD clamping failure disappears.
7.2.4 Bus Dominant Clamping
Due to a fail function on one of the CAN bus participants, the CAN bus could be permanent in “Dominant” state. The
external microcontroller doesn’t transmit any data to the CAN bus as long as the CAN bus remains “Dominant”. Even
if the permanent “Dominate” state on the CAN bus is caused by a short from CANH to V_CC, or similar, the transceiver
can not detect the failure, because the CAN bus failure detection works only when the transceiver is active sending
data to the bus. Therefore the TLE6251-2G has a bus dominant clamping detection unit installed. In case the bus
signal is “Dominant” for the time t > t_Bus,t the TLE6251-2G detects the bus clamping and sets the local failure flag.
The output driver stage remains active. In Receive - Only Mode the TLE6251-2G indicates the bus dominant
clamping by a logical “Low” signal on the NERR pin.
Data Sheet
19
Rev. 1.0, 2009-05-07