TJA1050 CAN Controller Interface Module

The TJA1050 is the interface between the CAN protocol controller and the physical bus. It is primarily intended for high-speed automotive applications using baud rates from 60 kbaud up to 1 Mbaud. It provides differential transmit capability to the bus and differential receiver capability to the CAN protocol controller. It is fully compatible to the “ISO 11898” standard. 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. A thermal protection circuit protects the IC from damage by switching off the transmitter if the junction temperature exceeds a value of approximately 165 °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. The pins CANH and CANL are protected from automotive electrical transients.

Control pin S allows two operating modes to be selected: high-speed mode or silent mode. The high-speed mode is the normal operating mode and is selected by connecting pin S to ground. It is the default mode if pin S is not connected. However, to ensure EMI performance in applications using only the high-speed mode, it is recommended that pin S is connected to ground. In the silent mode, the transmitter is disabled. All other IC functions continue to operate. The silent mode is selected by connecting pin S to VCC and can be used to prevent network communication from being blocked, due to a CAN controller which is out of control. A ‘TXD dominant time-out’ timer circuit prevents the bus lines being driven to a permanent dominant state (blocking all network communication) if pin TXD is forced permanently LOW by a hardware and/or software application failure. The timer is triggered by a negative edge on pin TXD. If the duration of the LOW-level on pin TXD exceeds the internal timer value, the transmitter is disabled, driving the bus into a recessive state. The timer is reset by a positive edge on pin TXD.