ADM3058E

Data Sheet

Rev. A | Page 14 of 18

THEORY OF OPERATION

CAN TRANSCEIVER OPERATION

The ADM3058E facilitates communication between a CAN

controller and the CAN bus. The CAN controller and the

ADM3058E 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, both the CANH pin and CANL pin 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 line 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 ADM3058E transceiver

has a ±25 V common-mode range (CMR) that exceeds the

ISO11898-2 requirement and further increases the tolerance

to ground variation.

See the AN-1123 Application Note for additional information

on CAN.

SIGNAL ISOLATION

The ADM3058E device provides galvanic signal isolation imple-

mented on the logic side of the interface. The RXD and TXD

channels are isolated using a low propagation delay on/off

keying (OOK) architecture with iCoupler digital isolation

technology.

The low propagation delay isolation, quick transceiver

conversion speeds, and integrated form factor are critical for

longer cable lengths, higher data speeds, and reducing the total

solution board space. The ADM3058E isolated transceiver

reduces solution board space while increasing data transfer

rates over discrete optocoupler and transceiver solutions.

INTEGRATED AND CERTIFIED IEC

ELECTROMAGNETIC COMPATIBILITY (EMC)

SOLUTION

Typically, designers must add protections against harsh operating

environments while also making the product as small as possible.

To reduce the board space and the design efforts needed to meet

system level ESD standards, the ADM3058E isolated transceiver

has robust protection circuitry on chip for the CANH and

CANL lines.

±40 V MISWIRE PROTECTION

High voltage miswire events commonly occur when the system

power supply is connected directly to the CANH and the CANL

bus lines during assembly. Supplies can also be shorted by

accidental damage to the field bus cables while the system is

operating. Accounting for inductive kick and switching effects,

the ADM3058E isolated transceiver CAN bus lines are protected

against these miswire or shorting events in systems with up to

nominal 24 V supplies. The CANH and CANL signal lines can

between the CAN bus lines without damage. This level of

protection applies when the device is either powered or

unpowered.

DOMINANT TIMEOUT

TXD line shorted to ground or malfunctioning CAN controller

are examples of how a single node can indefinitely prevent further

to the CAN bus by the transceiver. The TXD function restores

when the line is presented with a logic low.

Under normal operation, the CAN protocol allows five consecutive

bits of the same polarity before stuffing a bit of opposite polarity

into the transmitting bit sequence. When an error is detected, the

CAN controller purposely violates the bit stuffing rules by

producing six consecutive dominant bits. At any given data rate,

the CAN controller must transmit as many as 11 consecutive

dominant bits to effectively limit the ADM3058E minimum

data rate to 9600 bps.

FAIL-SAFE FEATURES

In cases where the TXD input pin is allowed to float to prevent

bus traffic interruption, the TXD input channel has an internal

recessive state.