Philips Semiconductors
Preliminary specification
High speed CAN transceiver
TJA1050
FUNCTIONAL DESCRIPTION
Control line S (pin 8) allows two operating modes to be
selected; high speed mode or silent mode.
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
40 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.
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 unconnected.
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
.
A current-limiting circuit protects the transmitter output
stage from damage caused by accidental short-circuit to
either positive or negative battery voltage, although power
dissipation increases during this fault condition.
A ‘TXD Dominant Time-out’ timer circuit prevents the bus
lines being driven to a permanent dominant state (blocking
all network communication) if TXD is forced permanently
LOW by a hardware and/or software application failure.
The timer is triggered by a negative edge on TXD. If the
duration of the LOW-level on 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
TXD.
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 TXD goes HIGH. The thermal protection
circuit is particularly needed when a bus line short-circuits.
The CANH and CANL lines are protected from automotive
electrical transients (according to “ISO 7637”; see Fig.6)
and are also protected from Electro-Static-Discharge
(ESD) of up to 4 kV from the human body.
Table 1 Function table of the CAN transceiver
(X = don’t care)
VCC
TXD
S
CANH
CANL
LOW
BUS STATE RXD
4.75 to 5.25 V
4.75 to 5.25 V
0
0 (or floating)
HIGH
dominant
recessive
recessive
recessive
recessive
0
1
1
X
X
X
1 (or floating)
X
1
X
X
X
0.5 × VCC
0.5 × VCC
0.5 × VCC
0.5 × VCC
4.75 to 5.25 V
<2 V (not powered)
2 V < VCC < 4.75 V
0 V <CANH< VCC 0 V <CANL< VCC
0 V <CANH< VCC 0 V <CANL< VCC
>2 V
1999 Sep 27
4
NXP [ NXP ]
