Data Sheet ADM3056E
Rev. 0 | Page 17 of 21
THEORY OF OPERATION
CAN TRANSCEIVER OPERATION
The ADM3056E facilitates galvanically isolated communication
between a CAN controller and the CAN bus. The CAN controller
and the ADM3056E communicate with standard 1.8 V, 2.5 V,
3.3 V, or 5.0 V CMOS levels.
The CAN bus has two states: dominant and recessive. The
recessive state is present on the bus when the differential voltage
between CANH and CANL is less than 0.5 V. In the recessive
state, the CANH and CANL pins are set to high impedance and
are loosely biased to a single-ended voltage of 2.5 V. A dominant
state is present on the bus when the differential voltage between
CANH and CANL is greater than 1.5 V. The transceiver transmits
a dominant state by driving the single-ended voltage of the
CANH pin to 3.5 V and the CANL pin to 1.5 V. The recessive
and dominant states correspond to CMOS high on the RXD pin
and CMOS low on the TXD pin, respectively.
A dominant state from another node overwrites a recessive state
on the bus. A CAN frame can be set for higher priority by using
a longer string of dominant bits to gain control of the CAN bus
during the arbitration phase. While transmitting, a CAN
transceiver also reads back the state of the bus. When a CAN
controller receives a dominant state while transmitting a
recessive state during arbitration, the CAN controller surrenders
the bus to the node still transmitting the dominant state. The
node that gains control during the arbitration phase reads back
only its own transmission. This interaction between recessive
and dominant states allows competing nodes to negotiate for
control of the bus while avoiding contention between nodes.
Industrial applications can have long cable runs. These long
runs can have differences in local earth potential. Different
sources may also power nodes. The ADM3056E transceiver
has a ±25 V common-mode range (CMR) that exceeds the
ISO 11898-2:2016 requirement and further increases the
tolerance to ground variation.
See the AN-1123 Application Note for additional information
on CAN.
SIGNAL ISOLATION
The ADM3056E device provides galvanic signal isolation
implemented on the logic side of the interface. The RXD and
TXD isolation channels transmit with an on off keying (OOK)
architecture on iCoupler digital isolation technology.
The low propagation delay isolation, quick transceiver conversion
speeds, and integrated form factor are critical for longer cable
lengths and higher data speeds and reducing the total solution
board space. The ADM3056E isolated transceiver reduces
solution board space while increasing data transfer rates over
discrete solutions.
The VDD1 pin powers the logic side signal isolation. The voltage
on this pin scales the digital interface logic from 1.7 V to 5.5 V,
depending on the supply voltage to the VDD1 pin.
TheVDD2 supply pin powers the bus side digital isolator and
CAN transceiver and must be supplied with a nominal 5 V supply.
STANDBY MODE
The STBY pin engages a reduced power standby mode that
modifies the operation of both the CAN transceiver and digital
isolation channels. Standby mode disables the TXD signal isolation
channel and sets the transmitter output to a high impedance state
loosely biased to GND2. While in standby mode, the receiver filters
bus data and responds only after the remote wake-up sequence
is received.
When entering or exiting standby mode, the TXD input must be
kept high and the RXD output must be ignored for the full tSTBY_ON
and tSTBY_OFF times.
REMOTE WAKE UP
The ADM3056E responds to the remote wake-up sequence as
defined in ISO 11898-2:2016. When the CAN transceiver is
presented with the defined slow speed, high to low to high
sequence within the low wake-up pattern detection reset
time (tWUPR), low speed data transmission is allowed.
Receipt of the remote wake-up pattern does not bring the
ADM3056E out of standby mode. The ADM3056E STBY pin
must be brought low externally to exit standby mode. After the
ADM3056E receives the remote wake-up pattern, the transceiver
continues to receive low speed data until standby mode is exited.
SILENT MODE
Asserting the SILENT pin disables the TXD digital isolation
channel. Any inputs to the TXD pin are ignored in this mode,
and the transceiver presents a recessive bus state. The operation
of the RXD channel is unaffected. The RXD channel continues
to output data received from the internal CAN transceiver
monitoring the bus.
Silent mode is useful when paired with a CAN controller using
automatic baud rate detection. A CAN controller must be set to
the same data rate as all attached nodes. The CAN controller
produces an error frame and ties up the bus with a dominant state
when the received data rate is different from expected. Other
CAN nodes then echo this error frame. While in silent mode,
the error frames produced by the CAN controller are kept from
interrupting bus traffic, and the controller can continue listening
to bus traffic.
RS
The RS pin sets the transceiver in one of three different modes
of operation: high speed, slope control, or standby. This pin
cannot be left floating.
For high speed mode, connect the RS pin directly to GND2.
Ensure that the transition time of the CAN bus signals is as
short as possible to allow higher speed signaling. A shielded cable
is recommended to avoid electromagnetic interference (EMI)
problems in high speed mode.