Datasheet

TLE6251D
Fail Safe Functions
Data Sheet 11 Rev. 1.0, 2012-07-27
5 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 heats up due to a continuous short
on the CANH or CANL, the internal overtemperature protection switches off the bus transmitter.
5.2 Unconnected Logical Pins
All logical 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 or floating, the TLE6251D enters the stand-by mode by default. In stand-by mode, the transmitter of the
TLE6251D is disabled, the bus bias is turned off and the input resistors of CANH and CANL are connected to GND.
The HS CAN transceiver TLE6251D will not influence the data on the CAN bus.
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 can have its root cause in a locked-up
microcontroller or in a short 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 TLE6251D disables the
transmitter (see Figure 6). The receive unit is still active and the data on the bus continue to be monitored by the
RxD output pin.
Figure 6 TxD Time-out function
Figure 6 shows how the transmitter is deactivated and re-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 TLE6251D requires a signal change on the TxD input pin from logical “low” to logical “high”.
TxD
t
t
CANH
CANL
RxD
t
TxD time-out
TxD time-out released
t > t
TxD