AMIS−30523
http://onsemi.com
34
FUNCTIONAL DESCRIPTION CAN TRANSCEIVER
Introduction
The CAN transceiver is the interface between a (CAN)
protocol controller and the physical bus. It provides
differential transmit capability to the bus and differential
receive capability to the CAN controller. Due to the wide
common−mode voltage range of the receiver inputs, it is
able to reach outstanding levels of electro−magnetic
susceptibility (EMS). Similarly, extremely low
electromagnetic emission (EME) is achieved by the
excellent matching of the output signals.
Additional features are the ideal passive behavior when
the supply voltage is removed; a wake−up over bus and the
extreme low current in stand−by mode.
To cope with the long bus delay the communication speed
needs to be low. The integrated transceiver allows low
transmit data rates down 10 kbit/s or lower.
Operating Modes
The CAN transceiver provides two modes of operation as
illustrated in Table 19. These modes are selectable through
pin STB
Table 19. OPERATING MODES
Mode STB
RXD
Low High
Normal Low Bus
dominant
Bus
recessive
Standby High Wake−up
request
detected
No
wake−up
request
detected
In the normal mode, the transceiver is able to
communicate via the bus lines. The signals are transmitted
and received to the CAN controller via the pins TxD and
RxD. The slopes on the bus lines outputs are optimized to
give extremely low EME.
In stand−by mode both the transmitter and receiver are
disabled and a very low−power differential receiver
monitors the bus lines for CAN bus activity. The bus lines
are terminated to ground and supply current is reduced to a
minimum, typically 10 mA. When a wake−up request is
detected by the low−power differential receiver, the signal
is first filtered and then verified as a valid wake signal after
a time period of t
BUS
, the RxD pin is driven low by the
transceiver to inform the controller of the wake−up request.
Split Circuit
The VSPLIT pin is operational only in normal mode. In
standby mode this pin is floating. The V
SPLIT
is connected
as shown in Figure 13 and its purpose is to provide a
stabilized DC voltage of 0.5 x V
CC
to the bus avoiding
possible steps in the common−mode signal therefore
reducing EME. These unwanted steps could be caused by an
un−powered node on the network with excessive leakage
current from the bus that shifts the recessive voltage from its
nominal 0.5 x V
CC
voltage.
Wake−up
Once a valid wake−up (dominant state longer than t
BUS
)
has been received during the standby mode the RxD pin is
driven low
Over−Temperature Detection
A thermal protection circuit protects the IC from damage
by switching off the transmitter if the junction temperature
exceeds a value of approximately 160°C. Because the
transmitter dissipates most of the power, the power
dissipation and temperature of the IC is reduced. All other
IC functions continue to operate. The transmitter off−state
resets when pin TxD goes high. The thermal protection
circuit is particularly needed when a bus line short circuits.
High Communication Speed Range
The transceiver is primarily intended for industrial
applications. It allows very low baud rates needed for long
bus length applications. But also high speed communication
is possible up to 1 Mbit/s.
Fail Safe Features
A current−limiting circuit protects the transmitter output
stage from damage caused by accidental short circuit to
either positive or negative supply voltage, although power
dissipation increases during this fault condition.
The pins CANH and CANL are protected from
automotive electrical transients (according to ISO 7637; see
Figure 7). Pins TxD and STB are pulled high internally
should the input become disconnected. Pins TxD, STB and
RxD will be floating, preventing reverse supply should the
V
CC
supply be removed.
DEVICE ORDERING INFORMATION
Part Number
Temperature
Range
Peak
Current
Package Type Shipping
†
AMIS30523C5231RG −40°C – 125°C 1600 mA
QFN−52
(Pb−Free)
Tape & Reel
AMIS30523C5231G −40°C – 125°C 1600 mA
QFN−52
(Pb−Free)
Tube
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
