TLE8250G_14 Datasheet, PDF (10/24 Pages) Infineon Technologies AG – High Speed CAN-Transceiver

TLE8250G
Fail Safe Functions
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 is heating up due to a continuos short
on CANH or CANL, the internal over-temperature protection switches off the bus transmitter.
5.2
Open Logic Pins
All logic input pins have internal pull-up resistor to V_CC. In case the V_CC supply is activated and the logical pins are
open or floating, the TLE8250G enters into the Stand-By mode per default. In Stand-By mode the output driver
stage of the TLE8250G is disabled, the bus biasing is shut off and the HS CAN transceiver TLE8250G 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 it’s root cause in a locked-up
microcontroller or in a short on the printed circuit board for example. In Normal Operation mode, a logical “Low”
signal on the TxD pin for the time t > t_TXD the TLE8250G activates the TxD Time-out and the TLE8250G disables
the output driver stage (see Figure 5). The receive unit is still active and the data on the bus are monitored at the
RxD output pin.
CANH
CANL
t > t_TxD
TxD Time - Out
TxD Time – Out released
t
TxD
t
RxD
t
Figure 5 TxD Time-Out function
Figure 5 shows how the output driver stage is deactivated and activated again. A permanent “Low” signal on the
TxD input pin activates the TxD time-out function and deactivates the output driver stage. To release the output
driver stage after a TxD time-out event the TLE8250G requires a signal change on the TxD input pin from logical
“Low” to logical “High”.
5.4
Under-Voltage detection
The HS CAN Transceiver TLE8250G is equipped with an under-voltage detection on the power supply V_CC. In
case of an under-voltage event on V_CC, the under-voltage detection changes the operation mode of TLE8250G to
the Stand-By mode, regardless of the logical signal on the pins NEN and NRM (see Figure 6). If the transceiver
TLE8250G recovers from the under-voltage event, the operation mode returns to the programmed mode by the
logical pins NEN and NRM.
Data Sheet
10
Rev. 1.1, 2014-10-09