TLE7250G Datasheet, PDF (10/22 Pages) Infineon Technologies AG – High Speed CAN Transceiver

TLE7250G
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 damage. If the device heats up due to a continuous short
on the CANH or CANL, the internal overtemperature protection switches off the transmitter.
5.2
Unconnected Logic Pins
All logic input pins have an internal pull-up resistor to V_CC. In case the V_CC supply is activated and the logical pins
are open or floating, the TLE7250G enters into the stand-by mode by default. In stand-by mode, the transmitter of
the TLE7250G is disabled, the bus bias is connected to GND and the HS CAN TLE7250G transceiver does 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 and the TLE7250G disables the transmitter
(see Figure 5). The receiver is still active and the data on the bus continues to be monitored by 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 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 TLE7250G requires a signal change on the TxD input pin from logical “low” to logical “high”.
5.4
Undervoltage Detection
The HS CAN Transceiver TLE7250G is provided with undervoltage detection at the power supply V_CC. In case of
an undervoltage event on V_CC, the undervoltage detection changes the operating mode of TLE7250G to the stand-
by mode, regardless of the logical signal on the NEN and NRM pins (see Figure 6). If the transceiver TLE7250G
recovers from the undervoltage condition, the operating mode is restored to the programmed mode by the logical
pins NEN and NRM.
Data Sheet
10
Rev. 1.0, 2012-03-01