AMIS-42675 Datasheet, PDF (5/12 Pages) AMI SEMICONDUCTOR – High-Speed Low Power CAN Transceiver

AMIS−42675
FUNCTIONAL DESCRIPTION
Operating Modes
AMIS−42675 provides two modes of operation as
illustrated in Table 5. These modes are selectable through
Pin STB.
Table 5. OPERATING MODES
Pin RXD
Mode
Pin STB
Low
High
Normal
Low
Bus Dominant
Bus Recessive
Standby
High
Wake−up Request Detected
No wake−up Request Detected
Normal Mode
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.
Standby Mode
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 V_SPLIT Pin is operational only in normal mode. In
standby mode this pin is floating. The V_SPLIT is connected
as shown in Figure 2 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.
Overtemperature 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 3). 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.
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.
http://onsemi.com
5