NXP Semiconductors
TJA1042
High-speed CAN transceiver with Standby mode
6. Functional description
The TJA1042 is a HS-CAN stand-alone transceiver with Standby mode. It combines the
functionality of the PCA82C250, PCA82C251 and TJA1040 transceivers with improved
EMC and ESD handling capability and quiescent current performance. Improved slope
control and high DC handling capability on the bus pins provide additional application
flexibility.
The TJA1042 is available in two versions, distinguished only by the function of pin 5:
•
The TJA1042T is 100 % backwards compatible with the TJA1040, and also covers
existing PCA82C250 and PCA82C251 applications
•
The TJA1042T/3 and TJA1042TK/3 allow for direct interfacing to microcontrollers with
supply voltages down to 3 V
6.1 Operating modes
The TJA1042 supports two operating modes, Normal and Standby, which are selectable
via pin STB. See
for a description of the operating modes under normal supply
conditions.
Table 3.
Mode
Normal
Standby
Operating modes
Pin STB
LOW
HIGH
Pin RXD
LOW
bus dominant
wake-up request
detected
HIGH
bus recessive
no wake-up request
detected
6.1.1 Normal mode
A LOW level on pin STB selects Normal mode. In this mode, the transceiver can transmit
and receive data via the bus lines CANH and CANL (see
for the block diagram).
The differential receiver converts the analog data on the bus lines into digital data which is
output to pin RXD. The slope of the output signals on the bus lines is controlled and
optimized in a way that guarantees the lowest possible EME.
6.1.2 Standby mode
A HIGH level on pin STB selects Standby mode. In Standby mode, the transceiver is not
able to transmit or correctly receive data via the bus lines. The transmitter and
Normal-mode receiver blocks are switched off to reduce supply current, and only a
low-power differential receiver monitors the bus lines for activity. The wake-up filter on the
output of the low-power receiver does not latch bus dominant states, but ensures that only
bus dominant and bus recessive states that persist longer than t
fltr(wake)bus
are reflected on
pin RXD.
In Standby mode, the bus lines are biased to ground to minimize the system supply
current. The low-power receiver is supplied by
V
IO
, and is capable of detecting CAN bus
activity even if
V
IO
is the only supply voltage available. When pin RXD goes LOW to signal
a wake-up request, a transition to Normal mode will not be triggered until STB is forced
LOW.
TJA1042_2
© NXP B.V. 2009. All rights reserved.
Product data sheet
Rev. 02 — 8 July 2009
5 of 20
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