MTC-3054
CAN Interface
Data Sheet
Features
• Technology: High voltage
BICMOS (HBIMOS)
• Line interface circuit for
Controller Area Network
(CAN - ISO/DIS 11898)
• Up to 500 Kbit/s data rates
• Integrated protection against
automotive disturbances,
including Load-dump
• Optimal design of transmitter
with programmable slope
minimizes RFI emission,
eliminating need for screened
cables
• Fully compatible with CAN
controller interface standards
• Tri-stateable driver
• 16 Pin SOP package
• Suitable for 12 V or 24 V
vehicle systems
Description
DR
AF
The parameters for the circuit are
specified under the special considera-
tion of ISO/DIS 11898 “Road vehicles
– Interchange of digital information –
Controller Area Network (CAN) for
high speed communication”.
The circuit consists of the following
blocks:
- a differential line transmitter
- a differential line receiver
- interface to the CAN protocol
handler
- fault handling features
The MTC-3054 is the implementation
of the CAN physical layer, used for
serial data interchange between elec-
tronic units in automotive applications.
The MTC-3054 was developed by
Alcatel Microelectronics in co-operation
with WABCO Westinghouse Fahr-
zeugbremsen GmbH.
Normal Operation Mode
The IC is especially designed to
provide the link between the protocol
IC (Controller Area Network IC) and
a physical bus line installed in the
vehicle. Data interchange between
the bus line and the protocol IC is
realized via the interface.
T
Application Specific Standard Products
The bus line can have two logical
states, dominant or recessive. The
bus is in the recessive state when the
driving sections of all transceivers
connected to this bus are passive. The
differential voltage between the two
wires is approximately zero. If at least
one driver is active the bus changes
into the dominant state. This state is
represented by a differential voltage
greater than a minimum threshold and
therefore by a current flow through the
terminating resistors of the bus line.
The recessive state is overwritten by
the dominant state.
The transceiver includes a bus driving
section D. The driving section will be
active if the transmission of a dominant
bit is required. This is defined by a
low level at input TX0A or TX0B. If,
as usual, only one of these inputs is
used, the common name will be TX0.
The transmitter is implemented as a
push (at CanH) and a pull (at CanL)
voltage driver, with a matched (but
opposite) slew rate, which can be
adjusted externally.
The bus receiving section R senses the
state of the bus lines. The reception
of a dominant state causes a low level
at RX0.
MTC-3054
VS
CPD
CANH
D
Logic
Unit
VCC
CANL
-
+
POR
CR
CD
Slope
Control
RF
/EN
TX0A
TX0B
RX1
RX0
OSC
Fig.1: Circuit Block Diagram
Bus system
R
CanH
R
CanL
Transceiver
Electronic
Unit
Electronic
Unit
3
TX0
RX0
RX1
/EN
R = Terminating resistor
CAN
Controller
µC
Fig.2: CAN Bus System
2
MTC-3054
A low level on TX0 and a low level on
RX0 correspond to a dominant state
on the bus lines.
To provide an independent switch-off
of the transceiver by a third device
(e.g. the µC) an enable input is
included.
In the disabled state the driving sec-
tion behaves as in the recessive state
and does not depend on the input
voltage at TX0. The output of the
receiving section is forced to the
recessive state and does not depend
on the bus
voltage. RX0 still outputs the data
corresponding to the input signal at
TX0A or TX0B. This is realized by
an internal logical connection.
In the enabled state the driving sec-
tion behavior depends on the input
voltage at TX0. The output of the
receiving section depends on the bus
voltage. RX0 only represents the data
of the receiver output. The internal
logical connection between TX0 and
RX0 is interrupted.
The enable input has an internal pull
up resistor to ensure a disabled state
when the input is not connected.
Pin VS is an additional supply pin.
This pin is used to supply the control
stage of the bus driver with a voltage
that is higher than the normal supply
voltage. This is needed to guarantee
proper functioning of the bus driver.
The pin VS can be supplied with a
DC voltage source, or with a voltage
generated with a charge pump. For
this purpose a square wave generator
is integrated on chip. The output is a
push pull CMOS output stage at pin
OSC. With the aid of two capacitors
and two (external or internal) diodes
a charge pump can be build to trans-
form the supply voltage VCC to a
higher level at VS.
Transmitter
TXO
Receiver
D
S
Q
-
+
Bus
POR
Common Mode
Overvoltage
Detector
Fig.3: Power-on Reset
3
MTC-3054
Fault behaviour
Error Condition Handling
When the voltage at the bus lines
moved out of the normal operating
range, the receiver is not allowed to
erroneously detect a dominant state.
To ensure this, an ‘out of range’ signal
is generated which will force the re-
ceiver to receive a recessive state. This
error condition will also prohibit the
driver from transmitting a dominant
bit on the bus as long as the ‘out of
range’ condition is present. Note that,
due to the limited speed of the ‘out of
range’ comparator, the receiver still
can erroneously detect (and transfer)
a dominant state within the period
defined by the reaction time needed
by the ‘out of range’ comparator.
To detect a short between the two bus
lines, the receiver will check the state of
the bus every time a dominant bit is sent
by the transmitter. This check will be
done at the end of the dominant pulse.
The transmitter is fully self protected.
It has a built in current limitation to
protect against short circuits. When the
voltage at the bus lines moves out of
the normal operating range, the trans-
mitter will put itself in a high impedant
state to avoid excessive dissipation and
to prevent breakdown.
Short Circuits
As specified in the maximum ratings,
short circuits of the bus wires CanH
and CanL to the positive supply
voltage Vbat or to ground must not
destroy the transceiver. To provide
sufficient safety for automotive
applications the voltage range for
permanent short circuits is extended
to 65 V dc. A short circuit between
CanH and CanL must not destroy the
IC as well. The maximum transient
voltages are specified on page 5.
These conditions must be fulfilled even
in case of missing voltage supply
and/or ground.
Reverse ECU Supply
If the connections for ground and sup-
ply voltage of an electronic unit (ECU)
(max. 40 V) which provides Vcc for
the transceiver are exchanged this
transceiver has a ground potential
which may be up to 40 V higher than
that of the other transceivers. In this
case no transceiver must be destroyed
even if several of them are connected
via the bus system.
Any exchange among the four con-
nections CanH, CanL, ground and
supply voltage of the electronic unit
at the connector of the unit must never
lead to a destruction of any trans-
ceiver of the bus system.
Faulty Supply
In case of a faulty supply (missing
connection of the electronic unit or
the transceiver to ground, missing
connection of Vbat of the electronic
unit, missing connection of Vcc of the
transceiver) the power supply module
of the electronic unit will operate such
that the transceiver is not supplied,
i.e. the voltage (Vcc - Vground) is
below the power-on reset level. In
this condition the bus connections
of the transceiver must be in the high
impedant state.
If the ground line of the electronic unit
is interrupted, Vbat may be applied to
the Vcc pin (measured relative to the
original ground potential, to which the
other units on the bus are connected).
Exchange possibilities
CanH
CanH
CanH
CanL
CanL
Ground
CanL
Ground
Supply voltage Vbat
Ground
Supply voltage Vbat
Supply voltage (Vbat)
The use of an inverse current protection
diode at the supply voltage input of
the electronic unit is recommended.
Power-on Reset
Until Vcc reaches the voltage level
VPORH, the bus connections CanH
and CanL are high impedant. When
Vcc is above this level the bus connec-
tions CanH and CanL are controlled.
If the voltage level at Vcc drops below
VPORL, the bus connections CanH
and CanL become high impedant. The
power-on reset comparator has a well
defined hysteresis.
Note that during power on reset, the
bus connections CanH and CanL are
high impedant for the voltage range
from -40 to +7 V. Outside this region,
protection circuits can be activated.
4
MTC-3054
ElectroMagnetic Compatibility (EMC)
The supply voltage Vcc is provided by
the electronic unit in which the interface
is located. It can be estimated, there-
fore, that Vcc is sufficiently filtered.
Disturbances in accordance
with DIN 40839 part 2/3
The interface ports CanH and CanL
withstand pulses specified in DIN
40839 parts 2 and 3. The voltages
are listed below.
Vp varies from -1 to 32 V.
The definitions of the parameters are
quoted from DIN 40839.
DIN 40893
Pulse
Pulse
Pulse
Pulse
1
2
3a
3b
Parameter
Vs
Vp+Vs
Vp+Vs
Vp+Vs
>=
<=
>=
<=
Part 2
- 40 V
+80 V
-150 V
+100 V
Part 3
- 30 V
+30 V
- 90 V
+60 V
Disturbances in accordance
with DIN 40839 part 4
The whole design is made under the
special consideration of the EMC
requirements which are specified in
DIN 40893 part 4. Therefore, the
following requirements must be met.
Note that these requirements cannot
be verified in final test by Alcatel
Microelectronics at the component
level.
Requirement
Frequency range
Signal level at
CanH or CanL
0.1 W
1W
No influence on IC function
No destruction of the IC
1 MHz ... 400 MHz
1 MHz ... 400 MHz
5
