NXP Semiconductors
TJA1055
Enhanced fault-tolerant CAN transceiver
Bus failures
Description
CANH wire
interrupted
CANH short-circuited
to battery
CANH short-circuited
to V
CC
CANL short-circuited
to ground
CANH short-circuited
to ground
CANL short-circuited
to battery
CANL short-circuited
to V
CC
CANL and CANH
mutually
short-circuited
Termination Termination
CANH (RTH) CANL (RTL)
on
on
on
on
on
weak
on
weak
on
weak
CANH
driver
on
on
off
off
on
on
on
on
on
CANL
driver
on
on
on
on
off
on
off
on
off
Receiver
mode
differential
differential
CANL
CANL
CANH
differential
CANH
differential
CANH
Table 4.
Failure
1
2
3
3a
4
5
6
6a
7
CANL wire interrupted on
weak
weak
on
on
on
on
on
[1]
[2]
A weak termination implies a pull-down current source behavior of 75
µA
typical.
A weak termination implies a pull-up current source behavior of 75
µA
typical.
Failure 6 is detected if the CANL bus line exceeds its comparator threshold for a certain
period of time. This delay is needed to avoid false triggering by external RF fields. After
detection of failure 6, the reception is switched to the single-wire mode through CANH; the
CANL driver is switched off and the RTL bias changes to the pull-up current source.
Recovery from failures 3, 3a and 6 is detected automatically after reading a consecutive
recessive level by corresponding comparators for a certain period of time.
Failures 4 and 7 initially result in a permanent dominant level on pin RXD. After a time-out
the CANL driver is switched off and the RTL bias changes to the pull-up current source.
Reception continues by switching to the single-wire mode via pins CANH or CANL. When
failures 4 or 7 are removed, the recessive bus levels are restored. If the differential voltage
remains below the recessive threshold level for a certain period of time, reception and
transmission switch back to the differential mode.
If any of the wiring failure occurs, the output signal on pin ERR will be set to LOW. On
error recovery, the output signal on pin ERR will be set to HIGH again. In case of an
interrupted open bus wire, this failure will be detected and signalled only if there is an
open wire between the transmitting and receiving node(s). Thus, during open wire
failures, pin ERR typically toggles.
During all single-wire transmissions, EMC performance (both immunity and emission) is
worse than in the differential mode. The integrated receiver filters suppress any HF noise
induced into the bus wires. The cut-off frequency of these filters is a compromise between
propagation delay and HF suppression. In single-wire mode, LF noise cannot be
distinguished from the required signal.
TJA1055_4
© NXP B.V. 2009. All rights reserved.
Product data sheet
Rev. 04 — 17 February 2009
6 of 26
PHILIPS [ NXP SEMICONDUCTORS ]
