ISL72026SEH

FN8762 Rev 3.00

Page 10 of 18

August 16, 2016

Functional Description

Overview

The Intersil ISL72026SEH is a 3.3V radiation tolerant CAN

transceiver that is compatible with the ISO11898-2 standard for

use in CAN (Controller Area Network) serial communication

systems.

The device performs transmit and receive functions between the

CAN controller and the CAN differential bus. It can transmit and

receive at bus speeds of up to 5Mbps. It is designed to operate

over a common mode range of -7V to +12V with a maximum of

120 nodes. The device is capable of withstanding ±20V on the

CANH and CANL bus pins outside of ion beam and ±16V under

ion beam.

Slope Adjustment

The output driver rise and fall time has three distinct selections

that may be chosen by using a resistor from the RS pin to GND.

Connecting the RS pin directly to GND results in output switching

times that are the fastest, limited only by the drive capability of

the output stage. RS = 10kΩ provides for a typical slew rate of

8V/µs and RS = 50kΩ provides for a typical slew rate of 4V/µs.

Putting a high logic level to the RS pin places the device in a low

current listen mode. The protocol controller uses this mode to

switch between low power listen mode and normal transmit

mode.

Cable Length

The device can work per ISO11898 specification with a 40m

cable and stub length of 0.3m and 60 nodes at 1Mbps. This is

greater than the ISO requirement of 30 nodes. The cable type

specified is twisted pair (shielded or unshielded) with a

characteristic impedance of 120Ω. Resistors equal to this are to

be terminated at both ends of the cable. Stubs should be kept as

short as possible to prevent reflections.

Cold Spare

High reliability system designers implementing data

communications have to be sensitive to the potential for single

point failures. To mitigate the risk of a failure they will use

redundant bus transceivers in parallel. In this arrangement both

active and quiescent devices can be present simultaneously on

the bus. The quiescent devices are powered down for cold spare

and do not affect the communication of the other active nodes.

To achieve this, a powered down transceiver (VCC < 200mV) has

a resistance between the CANH or CANL bus pin and the VCC

supply rail of > 480kΩ (max) with a typical resistance > 2MΩ. The

resistance between CANH and CANL of a powered-down

transceiver has a typical resistance of 80kΩ.

Listen Mode

When a high level is applied to the RS pin, the device enters a low

power listen mode. The driver of the transceiver is switched off to

conserve power while the receiver remains active. In listen mode

the transceiver draws 2mA (max) of current.

A low level on the RS pin brings the device back to normal

operation.

Loopback Mode

When a high level is applied to the LBK pin, the device enters the

loopback state. The transceiver CANH and CANL pins are

disconnected from the bus. The driver and receiver circuitry of

the transceiver remains active to allow for diagnostic testing of

the node.

Using 3.3V Devices in 5V Systems

Looking at the differential voltage of both the 3.3V and 5V

devices, the differential voltage is the same, the recessive

common mode output is the same. The dominant common

mode output voltage is slightly lower than the 5V counterparts.

The receiver specs are also the same. Though the electrical

parameters appear compatible it is advised that necessary

system testing be performed to verify interchangeable operation.

FIGURE 19A. OUTPUT SHORT CIRCUIT CURRENT TEST CIRCUIT

FIGURE 19B. OUTPUT SHORT CIRCUIT CURRENT WAVEFORMS

FIGURE 19. OUTPUT SHORT CIRCUIT CURRENT

Test Circuits and Waveforms (Continued)

D

CANH

CANL

GND

GND

+

-

VIN = -7V

OR 12V

IO(SRT)

IO(SRT)

|IO(SRT)|

0A

0V

VIN

VIN

12V

-7V

10ms