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Maxim > Design Support > Technical Documents > Application Notes > Automotive > APP 4643
Maxim > Design Support > Technical Documents > Application Notes > Interface Circuits > APP 4643
Keywords: 3V CAN, CAN, CAN Transceivers, TJA1041, TJA1040, TJA1050, PCA82C250, TLE625, CAN BUS,
Automotive networks, Automotive CAN, High ESD, low power CAN
APPLICATION NOTE 4643
Achieve ISO 11898-2-Compliant 5V HS-CAN
Communication from a 3.3V Supply
By:
Robert Regensburger, Automotive
Specialist, Automotive Product Definitions, Maxim Integrated
Products, Germany
Dec 06, 2010
Abstract: This application note solves a very common problem of powering an automotive electronic control
unit (ECU) with only a 3.3V supply. The ISO 11898-2 standard stipulates that only a 5V power supply rail
powers the CAN transceiver. This article shows how an automotive CAN transceiver can be supplied with a
3.3V charge pump to provide a low power, low-voltage, and easy solution to this problem. By eliminating the
5V power rail, many automotive OEMs will save weight and cost while improving mileage performance. The
article also discusses the circuit's impact on electromagnetic emissions (EME) and immunity (EMI) and
electromagnetic compatibility (EMC). The MAX13041 CAN transceiver is combined with the MAX1759 charge
pump in the application.
A similar article appeared in the July/August 2010 issue of Power Systems Design.
Introduction
From the first introduction of an automobile, manufacturers witnessed a rising demand for more comfort,
efficiency, environmental cleanliness, better performance, and safer vehicles. With each improvement, the
amount of wiring needed in vehicles began to increase significantly. After its invention by Bosch in the early
1980s, the CAN-bus network was quickly adopted by the auto industry because it reduced the weight and cost
of a wiring harness.
Older centralized control systems had all actuators and switches through multiple wires. The newer CAN-bus
system is a distributed system with electronic control units (ECUs) located at the place where each is needed
and connected through a two-wire bus system. This new system brought significant advantages and
addressed manufacturers' performance and cost goals, but it needed to be standardized to allow proper
communication among different suppliers' ECUs.
This standardization was first done in 1993 by the ISO (International Organization for Standardization)
organization. In 2003 a revision of the standard followed. Since then the ISO 11898 standard is the de facto
standard for all CAN communication in a vehicle; it is universally accepted by all OEMs.
To be compliant with the ISO 11898-2:2003 standard, the CAN transceiver bus driver usually needs to be
supplied by a 5V supply rail to provide the proper bus signaling levels. This specification is clear, but
implementing it is not always so straightforward. Most electronic systems engineers are familiar with the
problem when the subsystem's power requirements are not met by the main supply rails. In these cases the
available power rails often cannot directly supply a CAN transceiver. Simply put, there is only a single 3.3V
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