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TJA1054AT

Fault-tolerant CAN transceiver

Philips Electronics 

Philips Semiconductors

Fault-tolerant CAN transceiver

Product specification

TJA1054A

3. A local or remote wake-up event will be signalled at the transceiver pins RXD and NERR if VBAT = 5.3 V to 27 V.

4. In case the goto-sleep command was used before. When VCC drops, pin EN will become LOW, but due to the

fail-safe functionality this does not effect the internal functions.

5. VBAT power-on flag will be reset when entering normal operating mode.

Wake-up requests are recognized by the transceiver

through two possible channels:

• The bus lines for remote wake-up

• Pin WAKE for local wake-up.

In order to wake-up the transceiver remotely through the

bus lines, a filter mechanism is integrated. This

mechanism makes sure that noise and any present bus

failure conditions do not result into an erroneous wake-up.

Because of this mechanism it is not sufficient to simply pull

the CANH or CANL bus lines to a dominant level for a

certain time. To guarantee a successful remote wake-up

under all conditions, a message frame with a dominant

phase of at least the maximum specified tCANH or tCANL in

it is required.

A local wake-up through pin WAKE is detected by a rising

or falling edge with a consecutive level with 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.

If VCC is provided the wake-up request can be read on the

ERR or RXD outputs, 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 prevent EMC 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 th(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 tCANH or tCANL, 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)).

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.

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

165 °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.

2004 Mar 23

8

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