AMIS-42675 Datasheet, PDF (4/12 Pages) AMI SEMICONDUCTOR – High-Speed Low Power CAN Transceiver

AMIS-42675 High-Speed Low Power CAN Transceiver
For Long Networks
7.0 Functional Description
Data Sheet
7.1 Operating Modes
AMIS-42675 provides two modes of operation as illustrated in Table 4. These modes are selectable through pin STB.
Table 4: Operating Modes
Mode
Pin STB
Normal
Standby
Low
High
Low
Bus dominant
Wake-up request detected
Pin RXD
High
Bus recessive
No wake-up request detected
7.1.1. 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.
7.1.2. Stand-by 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 10µA. 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.
7.2 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.
7.3 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.
7.4 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.
7.5 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 1Mbit/s.
7.6 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 4). 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.
AMI Semiconductor –October 07, Rev. 1.0
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www.amis.com Specifications subject to change without notice