TLE7251V_15 Datasheet, PDF (16/36 Pages) Infineon Technologies AG – High Speed CAN-Transceiver with Bus Wake-up

5
Fail Safe Functions
TLE7251VLE
TLE7251VSJ
Fail Safe Functions
5.1
Short Circuit Protection
The CANH and CANL bus outputs are short circuit proof, either against GND or a positive supply voltage. A current
limiting circuit protects the transceiver against damages. If the device is heating up due to a continuous short on
the CANH or CANL, the internal overtemperature protection switches off the bus transmitter.
5.2
Unconnected Logic Pins
All logic input pins have an internal pull-up resistor to V_IO. In case the V_IO supply is activated and the logical pins
are open, the TLE7251V enters into the stand-by mode by default. In stand-by mode the transmitter of the
TLE7251V is disabled, the bus bias is turned off and the input resistors of CANH and CANL are connected to GND.
5.3
TxD Time-out Function
The TxD time-out feature protects the CAN bus against permanent blocking in case the logical signal on the TxD
pin is continuously “low”. A continuous “low” signal on the TxD pin might have its root cause in a locked-up
microcontroller or in a short circuit on the printed circuit board, for example. In normal-operating mode, a logical
“low” signal on the TxD pin for the time t > t_TxD enables the TxD time-out feature and the TLE7251V disables the
transmitter (see Figure 9). The receiver is still active and the data on the bus continues to be monitored by the
RxD output pin.
CANH
CANL
t > tTxD
TxD time-out
TxD time–out released
t
TxD
t
RxD
t
Figure 9 TxD time-out function
Figure 9 illustrates how the transmitter is deactivated and activated again. A permanent “low” signal on the TxD
input pin activates the TxD time-out function and deactivates the transmitter. To release the transmitter after a TxD
time-out event the TLE7251V requires a signal change on the TxD input pin from logical “low” to logical “high”.
Data Sheet
16
Rev. 1.0, 2015-09-10