Datasheet

TLE6251D
Functional Description
Data Sheet 7 Rev. 1.0, 2012-07-27
The TLE6251D is a High Speed CAN transceiver, operating as an interface between the CAN controller and the
physical bus medium. A HS CAN network is a two-wire, differential network, which allows data transmission rates
up to 1 Mbps. The characteristics for a HS CAN network are the two signal states on the CAN bus: “dominant” and
“recessive” (see Figure 3).
The CANH and CANL pins are the interface to the CAN bus and both pins operate as an input and output. The
RxD and TxD pins are the interface to the microcontroller. The TxD pin is the serial data input from the CAN
controller, the RxD pin is the serial data output to the CAN controller. As shown in Figure 1, the HS CAN
transceiver TLE6251D includes a receiver and a transmitter unit, allowing the transceiver to send data to the bus
medium and monitor the data from the bus medium at the same time. The HS CAN transceiver TLE6251D
converts the serial data stream which is available on the transmit data input TxD, into a differential output signal
on the CAN bus, provided by the pins CANH and CANL. The receiver stage of the TLE6251D monitors the data
on the CAN bus and converts them to a serial, single-ended signal on the RxD output pin. A logical “low” signal
on the TxD pin creates a “dominant” signal on the CAN bus, followed by a logical “low” signal on the RxD pin (see
Figure 3). The feature, broadcasting data to the CAN bus and listening to the data traffic on the CAN bus
simultaneously is essential to support the bit-to-bit arbitration within CAN networks.
The voltage levels for HS CAN transceivers are defined by the ISO 11898-2 and the ISO 11898-5 standards.
Whether a data bit is “dominant” or “recessive” depends on the voltage difference between the CANH and CANL
pins:
V
DIFF
= V
CANH
- V
CANL
.
In comparison with other differential network protocols, the amplitude of the differential signal on a CAN network
can only be higher than or equal to 0 V. To transmit a “dominant” signal to the CAN bus, the amplitude of the
differential signal
V
DIFF
is higher than or equal to 1.5 V. To receive a “recessive” signal from the CAN bus, the
amplitude of the differential
V
DIFF
is lower than or equal to 0.5 V.
“Partially-supplied” High Speed CAN networks are networks in which the CAN bus nodes of one common network
have different power supply conditions. Some nodes are connected to the common power supply, while other
nodes are disconnected from the power supply and in power-down state. Regardless of whether the CAN bus
subscriber is supplied or not, each subscriber connected to the common bus media must not interfere with the
communication. The TLE6251D is designed to support “partially-supplied” networks. In the power-down state, the
receiver input resistors are switched off and the transceiver input has a high resistance.
For permanently supplied ECUs, the HS CAN transceiver TLE6251D provides a stand-by mode. In stand-by
mode, the power consumption of the TLE6251D is optimized to a minimum, while the device is still able to
recognize wake-up patterns on the CAN bus and signal a wake-up event to the external microcontroller.
The voltage level on the digital input TxD and the digital output RxD is determined by the power supply level at the
V
IO
pin. Depending on the voltage level at the V
IO
pin, the signal levels on the logic pins (STB, TxD and RxD) are
compatible with microcontrollers having a 5 V or 3.3 V I/O supply. Usually, the
V
IO
power supply of the transceiver
is connected to the same power supply as the I/O power supply of the microcontroller.