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ADM3055E/ADM3057E

Data Sheet

Rev. A | 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

technology.

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.

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