ADM3055E/ADM3057E Data Sheet
Rev. B | Page 20 of 24
THEORY OF OPERATION
CAN TRANSCEIVER OPERATION
The ADM3055E/ADM3057E facilitate communication between
a CAN controller and the CAN bus. The CAN controller and
the ADM3055E/ADM3057E communicate with standard 1.8 V,
2.5 V, 3.3 V, or 5.0 V CMOS levels. The internal transceiver
translates the CMOS levels to and from the CAN bus.
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 and CMOS low,
respectively, on the RXD pin and TXD pin.
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 may have differences in local earth potential. Different
sources may also power nodes. The ADM3055E 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 AND POWER ISOLATION
The ADM3055E and the ADM3057E provide galvanic signal
isolation implemented on the logic side of the interface. The RXD
and TXD isolation channels transmit and receive with an on/off
keying (OOK) architecture on the iCoupler digital isolation
technolog y.
The ADM3055E and the ADM3057E feature independent power
supply pins for isolated power (the VCC pin) and isolated signal
(the VIO pin). The VCC pin requires a nominal 5 V supply to
produce the 5 V isolated power. The VIO pin may be supplied
with a nominal 1.8 V to a nominal 5 V. The logic input and
output levels scale to the voltage supplied to the VIO pin. The
isolated power from the VISOOUT pin must be supplied to the
VISOIN pin to power the bus side digital isolator and transceiver.
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. STBY does not control or modify behavior of
the isoPower integrated dc-to-dc converter. The dc-to-dc converter
continues to operate and provide the power to the bus side.
REMOTE WAKE UP
The ADM3055E and the ADM3057E respond to the remote
wake-up sequence as defined in ISO 11898-2:2016. When CAN
channels are presented with the defined slow speed high low
high sequence within the low wake-up pattern detection reset
time (tWUPR), low speed data transmission is allowed.
Successful receipt of the remote wake-up pattern does not bring
the ADM3055E and the ADM3057E out of standby mode. The
ADM3055E STBY pin must be brought low externally to exit
standby mode. After the ADM3055E or ADM3057E device
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 to tune.