FN8861 Rev. 1.00

Page 21 of 28

Jul 27, 2017

ISL72026ASEH

4. Functional Description

4.

Functional Description

4.1

Overview

The Intersil ISL72026ASEH is a 3.3V radiation tolerant CAN transceiver that is compatible with the ISO11898-2

standard for use in Controller Area Network (CAN) 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 up to 5Mbps. It is designed to operate across 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.

4.2

Slope Adjustment

The transceiver driver has three programmable rise/fall time options programmed by the resistor value connected

from the RS pin to GND. A 0Ω resistor sets the part in Fast Speed Mode. A resistor of 10kΩ sets the part in

Medium Speed Mode. A resistor of 50kΩ puts the part in Slow Speed Mode. Putting a high logic level on the RS

pin places the part in Listen mode. Refer to “Listen Mode” on page 22 for more information.

4.2.1

Fast Speed Mode

Connecting the RS pin directly to GND (0Ω resistor) results in the fastest driver output switching times, limited

only by the drive capability of the output state. In Fast Speed mode (RS = 0V), the rise/fall times, propagation

delays, and total loop delays are optimized for a data rate of 1Mbps.

4.2.2

Medium Speed Mode

In Medium Speed mode (RS = 10kΩ), the rise/fall times, propagation delays, and total loop delays are

optimized for a data rate of 500kbps. RS = 10kΩ provides for a typical slew rate of 12V/µs. The slower edges in

Medium Speed mode at 500kbps provide better EMI results than running at 500kbps in Fast Speed mode.

4.2.3

Slow Speed Mode

In Slow Speed mode (RS = 50kΩ), the rise/fall times, propagation delays, and total loop delays are optimized

for a data rate of 250kbps. RS = 50kΩ provides for a typical slew rate of 8V/µs. The slower edges in Slow

Speed mode at 250kbps provide better EMI results than running at 250kbps in Medium Speed mode.

4.3

Cable Length

The device can operate according to the ISO11898 specification with a 40m cable and stub length of 0.3m and 60

nodes at 1Mbps. These specifications are 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 impedance

must be terminated at both ends of the cable. Keep stubs as short as possible to prevent reflections.

4.4

Cold Spare

To reduce the risk of a single-point failure, 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 as

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

The powered down transceiver (VCC <200mV) has a resistance between the CANH or CANL bus pin to the VCC

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

powered-down transceiver is typically 80kΩ. The receiver output (R pin) of a powered-down transceiver

(VCC < 200mV) is internally connected to ground. Therefore, the receiver outputs of an active transceiver and a

cold spare transceiver cannot be connected together in the redundant application.