AMIS-42671 Datasheet, PDF (4/12 Pages) AMI SEMICONDUCTOR – High-Speed CAN Transceiver

AMIS-42671 High-Speed CAN Transceiver
For Long Networks
Data Sheet
7.0 Functional Description
7.1 Operating Modes
The behavior of AMIS-42671 under various conditions is illustrated in Table 3 below. In case the device is powered, one of two
operating modes can be selected through pin AUTB.
Table 3: Functional table of AMIS-42671 when not connected to the bus; X = don’t care
VCC
pin TxD
pin AUTB
pin CANH
pin CANL
Bus state
pin RxD
4.75 to 5.25.V
0
0 (or floating) High
Low
Dominant
0
4.75 to 5.25.V
X
1
VCC/2
VCC/2
Recessive
1
4.75 to 5.25.V
1 (or floating) X
VCC/2
VCC/2
Recessive
1
VCC<PORL (unpowered) X
X
0V<CANH<VCC
0V<CANL<VCC
Recessive
1
PORL<VCC<4.75V
>2V
X
0V<CANH<VCC
0V<CANL<VCC
Recessive
1
7.1.1. High-Speed Mode
If pin AUTB is pulled low (or left floating), the transceiver is in its high-speed mode and 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 line outputs are optimized
to give extremely low electromagnetic emissions.
7.1.2. Autobaud Mode
If pin AUTB is pulled high, AMIS-42671 is in Autobaud mode. The transmitter is disabled while the receiver remains active. All other IC
functions also continue to operate. Normal bus activity can be monitored at the RxD pin and transmit data on TxD is looped back to
RxD without influencing the CAN communication.
TxD
CANH
CANL
RxD
AUTB
PC20071002.4
Figure 4: Simplified Schematic Diagram of Autobaud Function
In Autobaud mode the local CAN controller is able to detect the used communication speed of other transmitting network nodes. Bus
communication is received and via the RxD pin sent to the CAN controller. If the CAN controller operates at the wrong baud rate, it will
transmit an error frame. This message will be looped back to the CAN controller which will increment its error counter. The CAN
controller will be reset with another baud rate. When an error-free message is received, the correct baud rate is detected. A logic low
may now be applied to pin AUTB, returning to the High-Speed Mode.
7.2 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 necessary when a bus line short-circuits.
AMI Semiconductor – Oct. 07, Rev. 1.0
4
www.amis.com Specifications subject to change without notice