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TJA1145A All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2020. All rights reserved.
Product data sheet Rev. 2 — 23 September 2020 10 of 57
NXP Semiconductors
TJA1145A
High-speed CAN transceiver for partial networking
7.2 High-speed CAN transceiver
The integrated high-speed CAN transceiver is designed for active communication at bit
rates up to 1 Mbit/s, providing differential transmit and receive capability to a CAN protocol
controller. The transceiver is ISO 11898-2:2016 compliant (defining high-speed CAN with
selective wake-up functionality and autonomous bus biasing). The CAN transmitter is
supplied via pin VCC while the CAN receiver is supplied via pin BAT. The TJA1145A
includes additional timing parameters on loop delay symmetry to ensure reliable
communication in fast phase at data rates up to 5 Mbit/s, as used in CAN FD networks.
The CAN transceiver supports autonomous CAN biasing, which helps to minimize RF
emissions. CANH and CANL are always biased to 2.5 V when the transceiver is in Active
or Listen-only modes (CMC = 01/10/11).
Autonomous biasing is active in CAN Offline mode - to 2.5 V if there is activity on the bus
(CAN Offline Bias mode) and to GND if there is no activity on the bus for t > t
to(silence)
(CAN Offline mode).
This is useful when the node is disabled due to a malfunction in the microcontroller or
when CAN partial networking is enabled. The TJA1145A ensures that the CAN bus is
correctly biased to avoid disturbing ongoing communication between other nodes. The
autonomous CAN bias voltage is derived directly from V
BAT
.
7.2.1 CAN operating modes
The integrated CAN transceiver supports four operating modes: Active, Listen-only,
Offline and Offline Bias (see
Figure 5). The CAN transceiver operating mode depends on
the TJA1145A operating mode and on the setting of bits CMC in the CAN control register
(
Tab le 7).
When the TJA1145A is in Normal mode, the CAN transceiver operating mode (Offline,
Active or Listen-only) can be selected via bits CMC in the CAN control register (
Tabl e 7).
When the TJA1145A is in Standby or Sleep modes, the transceiver is forced to Offline or
Offline Bias mode (depending on bus activity).
7.2.1.1 CAN Active mode
In CAN Active mode, the transceiver can transmit and receive data via CANH and CANL.
The differential receiver converts the analog data on the bus lines into digital data, which
is output on pin RXD. The transmitter converts digital data generated by the CAN
controller (input on pin TXD) into analog signals suitable for transmission over the CANH
and CANL bus lines.
CAN Active mode is selected when CMC = 01 or 10. When CMC = 01, V
CC
undervoltage
detection is enabled and the transceiver switches to CAN Offline or CAN Offline Bias
mode when the voltage on V
CC
drops below V
uvd(VCC)
. When CMC = 10, V
CC
undervoltage detection is disabled. The transmitter will remain active until the TJA1145A
is forced into Sleep mode by the V
CC
undervoltage event; the transceiver will then switch
to CAN Offline or CAN Offline Bias mode.
The CAN transceiver is in Active mode when:
• the TJA1145A is in Normal mode (MC = 111) and the CAN transceiver has been
enabled by setting bits CMC in the CAN control register to 01 or 10 (see
Tabl e 7) and: