AMISï42673
http://onsemi.com
5
FUNCTIONAL DESCRIPTION
General
The AMISï42673 is the interface between the CAN
protocol controller and the physical bus. It is intended for
use in industrial and automotive applications requiring baud
rates up to 1 Mbit/s. It provides differential transmit
capability to the bus and differential receiver capability to
the CAN protocol controller. It is fully compatible to the
“ISO 11898ï2” standard.
Operating Modes
AMISï42673 only operates in highïspeed mode as
illustrated in Table 5.
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.
Table 5. FUNCTIONAL TABLE OF AMISï42673; x = don’t care
V
CC
Pin TxD Pin CANH Pin CANL Bus State Pin RxD
4.75 to 5.25 V 0 High Low Dominant 0
4.75 to 5.25 V 1
(or floating)
V
CC
/2 V
CC
/2 Recessive 1
V
CC
< PORL (Unpowered) x 0 V < CANH < V
CC
0 V < CANL < V
CC
Recessive 1
PORL < V
CC
< 4.75 V > 2 V 0 V < CANH < V
CC
0 V < CANL < V
CC
Recessive 1
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 offïstate
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.
FailïSafe Features
A currentïlimiting circuit protects the transmitter output
stage from damage caused by accidental shortïcircuit to
either positive or negative supply voltage ï 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).
Should TxD become disconnected, this pin is pulled high
internally.
When the V
CC
supply is removed, Pins TxD and RxD will
be floating. This prevents the AMISï42673 from being
supplied by the CAN controller through the I/O Pins.
3.3 V Interface
AMISï42673 may be used to interface with 3.3 V or 5 V
controllers by use of the V
33
pin. This pin may be supplied
with 3.3 V or 5 V to have the corresponding digital interface
voltage levels.
When the V
33
pin is supplied at 2.5 V, even interfacing
with 2.5 V CAN controllers is possible. See also Digital
Output Characteristics @ V
33
= 2.5 V, Table . In this case a
pullïup resistor from TxD to V
33
is necessary.
