Data Sheet

ADM3053

Rev. E | Page 13 of 18

CIRCUIT DESCRIPTION

CAN TRANSCEIVER OPERATION

A CAN bus has two states called dominant and recessive. A

dominant state is present on the bus when the differential voltage

between CANH and CANL is greater than 0.9 V. A recessive state

is present on the bus when the differential voltage between CANH

and CANL is less than 0.5 V. During a dominant bus state, the

CANH pin is high, and the CANL pin is low. During a recessive

bus state, both the CANH and CANL pins are in the high

impedance state.

high-speed and slope control. For high-speed operation, the

transmitter output transistors are simply switched on and off as

fast as possible. In this mode, no measures are taken to limit the

rise and fall slopes. A shielded cable is recommended to avoid

electromagnetic interference (EMI) problems. High-speed mode

is selected by connecting Pin 18 to ground.

Slope control mode allows the use of an unshielded twisted pair

or a parallel pair of wires as bus lines. To reduce EMI, the rise

and fall slopes must be limited. The rise and fall slopes can be

programmed with a resistor connected from Pin 18 to ground.

The slope is proportional to the current output at Pin 18.

SIGNAL ISOLATION

The ADM3053 signal isolation is implemented on the logic side of

the interface. The part achieves signal isolation by having a digital

isolation section and a transceiver section (see Figure 1). Data

applied to the TxD pin referenced to logic ground (GND1) are

coupled across an isolation barrier to appear at the transceiver

section referenced to isolated ground (GND2). Similarly, the single-

ended receiver output signal, referenced to isolated ground in

the transceiver section, is coupled across the isolation barrier to

appear at the RxD pin referenced to logic ground (GND1). The

interface to 3.3 V or 5 V logic.

POWER ISOLATION

The ADM3053 power isolation is implemented using an isoPower

integrated isolated dc-to-dc converter. The dc-to-dc converter

section of the ADM3053 works on principles that are common to

most modern power supplies. It is a secondary side controller

architecture with isolated pulse-width modulation (PWM)

switches current into a chip-scale air core transformer. Power

transferred to the secondary side is rectified and regulated to 5 V.

side by a dedicated iCoupler data channel. The PWM modulates

the oscillator circuit to control the power being sent to the

secondary side. Feedback allows for significantly higher power

and efficiency.

The ADM3053 integrated dc-to-dc converter is designed as a

self contained solution and must not drive an external load. To

meet additional isolated power needs, isoPower isolated dc-to-

dc converters are available in a variety of power or power plus

standard data channel options.

TRUTH TABLES

The truth tables in this section use the abbreviations found in

Table 9.

Table 9. Truth Table Abbreviations

Letter

Description

H

High level

L

Low level

X

Don’t care

Z

High impedance (off)

I

Indeterminate

NC

Not connected

Table 10. Transmitting

Supply Status

Input

Outputs

TxD

Bus State

CANH

CANL

On

On

L

Dominant

H

L

On

On

H

Recessive

Z

Z

On

On

Floating

Recessive

Z

Z

Off

On

X

Recessive

Z

Z

On

Off

L

Indeterminate

I

I

Table 11. Receiving

Supply Status

Inputs

Output

Bus State

RxD

On

On

≥ 0.9 V

Dominant

L

On

On

≤ 0.5 V

Recessive

H

On

On

I

On

On

Inputs open

Recessive

H

Off

On

I

On

Off

H

1

X means don’t care.

THERMAL SHUTDOWN

The ADM3053 contains thermal shutdown circuitry that protects

the part from excessive power dissipation during fault conditions.

Shorting the driver outputs to a low impedance source can result in

high driver currents. The thermal sensing circuitry detects the

increase in die temperature under this condition and disables the

driver outputs. This circuitry is designed to disable the driver

outputs when a die temperature of 150°C is reached. As the

device cools, the drivers are reenabled at a temperature of 140°C.