TJA1055
NXP Semiconductors
Enhanced fault-tolerant CAN transceiver
A local wake-up through pin WAKE is detected by a rising or falling edge with a
consecutive level exceeding the maximum specified tWAKE
.
On a wake-up request the transceiver will set the output on pin INH to HIGH which can be
used to activate the external supply voltage regulator.
A wake-up request is signalled on ERR or RXD with an active LOW signal. So the external
microcontroller can activate the transceiver (switch to normal operating mode) via
pins STB and EN.
To prevent a false remote wake-up due to transients or RF fields, the wake-up voltage
levels have to be maintained for a certain period of time. In the low power modes the
failure detection circuit remains partly active to prevent an increased power consumption
in the event of failures 3, 3a, 4 and 7.
To prevent a false local wake-up during an open wire at pin WAKE, this pin has a weak
pull-up current source towards VBAT. However, in order to protect the transceiver against
any EMC immunity issues, it is recommended to connect a not used pin WAKE to pin
BAT. Pin INH is set to floating only if the goto-sleep command is entered successfully. To
enter a successful goto-sleep command under all conditions, this command must be kept
stable for the maximum specified td(sleep)
.
Pin INH will be set to a HIGH level again by the following events only:
• VBAT power-on (cold start)
• Rising or falling edge on pin WAKE
• A message frame with a dominant phase of at least the maximum specified tdom(CANH)
or tdom(CANL), while pin EN or pin STB is at a LOW level
• Pin STB goes to a HIGH level with VCC active
To provide fail-safe functionality, the signals on pins STB and EN will internally be set to
LOW when VCC is below a certain threshold voltage (VCC(stb)). An unused output pin INH
can simply be left open within the application.
7.3 Power-on
After power-on (VBAT switched on) the signal on pin INH will become HIGH and an internal
power-on flag will be set. This flag can be read in the power-on standby mode through
pin ERR (STB = 1; EN = 0) and will be reset by entering the normal operating mode.
7.4 Protections
A current limiting circuit protects the transmitter output stages against short-circuit to
positive and negative battery voltage.
If the junction temperature exceeds the typical value of 175 °C, the transmitter output
stages are disabled. Because the transmitter is responsible for the major part of the power
dissipation, this will result in a reduced power dissipation and hence a lower chip
temperature. All other parts of the device will continue to operate.
The pins CANH and CANL are protected against electrical transients which may occur in
an automotive environment.
TJA1055_4
© NXP B.V. 2009. All rights reserved.
Product data sheet
Rev. 04 — 17 February 2009
8 of 26
NXP [ NXP ]
