Freescale Advances Automotive Airbag Technology

Tokyo (Freescale Technology Forum Japan) -- As automotive airbag systems continue to grow more sophisticated and require more sensors for collision detection, automakers face pressures to reduce cost while enhancing passenger safety. Freescale Semiconductor is responding to this market need with next-generation safety bus interface devices designed to bring robust, high-speed communications for the growing number of collision sensors planned to be used in new vehicles.

Freescale's MC33781 master interface device and MC33784 slave interface for remote sensing allow airbag manufacturers to add more collision sensors while reducing system cost and enhancing the system's noise immunity. Both products are designed for airbag safety systems that use the widely adopted Distributed Systems Interface (DSI) standard to connect remotely placed pressure, acceleration, occupant, and buckle sensors to the main airbag electronic control unit.

"With the move toward smaller, more fuel-efficient vehicles, the emphasis on safety features will continue to grow, and vehicle OEMs and their suppliers will increasingly adopt application-optimized standard protocols, such as DSI, to minimize the cost and complexity of implementing these enhanced systems," said Chris Webber, Vice President, Global Automotive Practice, Strategy Analytics. "We predict there will be some two billion nodes per year connected in car electronic networks, across all applications, by 2014. As the leading automotive IC supplier, Freescale is well positioned to take advantage of this growth in automotive networking and to support the needs of designers of today's and tomorrow's airbag systems."

The DSI protocol, the leading automotive safety bus, was pioneered by Freescale and TRW. The DSI protocol supports point-to-point, parallel, and daisy chain networks. DSI has been adopted by the world's leading manufacturers of supplemental restraint system airbags, including TRW and DENSO Corp. DSI-compliant products have been in production for many years.

"We have used DSI-based devices for numerous airbag modules, and the demand for these devices will continue to increase to meet growing requirements for safety and advanced airbag systems," said Mitsuhiko Masegi, Managing Officer, DENSO Corp. "We believe Freescale's new products for airbag applications will satisfy market needs, as well as future airbag requirements for high performance and functionality. We expect Freescale, as the leader in automotive semiconductors, will continue to develop innovative solutions that enable safer automobiles."

A dozen automotive OEMs have included DSI-based systems in their vehicles. Designed in collaboration with a key airbag system customer, the new MC33781 and MC33784 devices incorporate the next-generation DSI 2.02 protocol.

"The DSI safety bus helps airbag manufacturers reduce costs and speed time to market through an open, stable, and well-adopted safety bus standard," said Arman Naghavi, Vice President and General Manager of Freescale's Analog and Mixed-Signal Products Division. "Our latest DSI-based products are designed to help reduce the vehicle maker's cost of adding more sensors to the car's airbag system, while offering exceptional electromagnetic interference (EMI) performance and fault tolerance."

Manufactured on Freescale's SMARTMOS 8 technology, Freescale's latest DSI interface products offer more channels at a lower cost per channel, an improved EMI signature, and higher top-end bus speeds. The four-channel MC33781 master interface device can support data transfers at up to 200 Kbps. Each MC33784 slave device has two 10-bit analog inputs and three logic inputs or outputs.

The DSI devices' differential operation is designed to reduce EMI, as well as support fault tolerance and detection of shorts in the system. Frequency spreading further reduces interference by spreading the energy across many frequencies, thereby reducing the energy in any single frequency.

Comprehensive Silicon Solutions for Airbag Systems
Freescale is a leading supplier of semiconductor products for airbag applications, including the main electronic control unit (ECU) to satellite airbag modules. The company's offerings for airbag systems include 16-bit S12 and 32-bit Power Architecture microcontrollers, pressure and acceleration sensors, and analog devices based on SMARTMOS technology. Freescale is well positioned to supply the critical semiconductor elements of next-generation airbag systems.

Integration of safety systems such as pre-crash detection and electronic stability program sensor clusters into the airbag ECU continues to drive system complexity and increase the number of required sensors. Demand for airbag-related systems is driven by legislation, consumer influences, and automotive growth in emerging markets. According to Strategy Analytics, by 2010 airbag electronic control unit demand will reach 66 million units; airbag satellite demand will reach 132 million units; and the total available market for silicon used in airbag systems will grow to $1.14 billion.


MC33781 Master Interface Product Features
  • Four independent differential DSI channels, with a pseudo bus switch feature on channel 0
  • Data rate up to 200 Kbps full duplex per channel
  • Dual serial peripheral interface
  • Enhanced bus fault performance
  • Automatic message cyclical redundancy checking (CRC) generation and checking for each channel
  • Enhanced register set, with addressable buffer, which enables queuing of four independent slave commands at one time for each channel
  • 8-bit to 16-bit messages with 0–8 bits of CRC
  • Independent frequency spreading for each channel
  • 32-Id SOICW exposed pad


MC33784 Satellite Sensor Slave Interface Product Features
Sensor interface
  • Two-channel, 10-bit analog-to-digital converter
  • Three pins configurable as logic inputs or outputs
  • Regulated 5 V output


Bus interface
  • Single-ended or differential receiver
  • High- and low-side bus switches for improved common-mode noise rejection
  • 10 MHz internal clock, with dithering for improved EMI performance
  • DSI daisy chain device


Fault modes
  • Under-voltage detection

Pricing and Availability
Samples of the MC33781 and MC33784 devices are available now to automotive customers. For product pricing, please contact local Freescale sales representatives.

For more information about Freescale's DSI portfolio, visit the company's Web site.

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