MC33781 and MC33784 Distributed System Interface (DSI) Master-Slave for Automotive Airbag System - Freescale

Freescale recently introduced the MC33781 Distributed System Interface (DSI)
Master and the MC33784 DSI Slave chips for automotive airbag
applications. MC33781 and MC33784 Distributed Systems Interface devices enable
addition of more collision sensors while enhancing noise immunity and
reducing cost. MC33781 and MC33784 DSI Master-Slave chips are designed for
airbag safety systems that use the widely adopted DSI standard to connect remotely placed pressure,
acceleration, occupant and buckle sensors to the main airbag electronic control
unit. MC33781 DSI Master has four-channel. The device is able to support data transfers at up to
200 kbps. Each MC33784 DSI Slave has two 10-bit analog inputs
and three logic inputs or outputs. Designed in collaboration with a key airbag
system customer, the new MC33781 and MC33784 incorporate the next-gen DSI
Version 2.02 protocol.

Arman
Naghavi, Freescale, said:

The DSI safety bus helps airbag manufacturers reduce costs and speed time to
market through an open, stable and well adopted safety bus standard… 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 EMI performance
and fault tolerance.

Freescale’s latest DSI
interface products offer more channels at a lower cost per channel, an improved
electromagnetic interference (EMI) signature and higher top-end bus speeds. 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.

About DSI (Distributed System Interface) protocol
The Distributed System Interface (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 (SRS) airbags,
including TRW and DENSO Corporation. DSI-compliant products have been in
production for many years.

Freescale offers chips for airbag
applications, including the main ECU (Electronic Control Unit) to satellite
airbag modules.
Freescale’s offerings for airbag systems include 16-bit S12
and 32-bit Power Architecture microcontrollers, pressure and
acceleration sensors, and analog devices based on company’s SMARTMOS technology.

MC33781 - Quad DSI (Distributed System Interface) 2.02 Master with
Differential Drive and Frequency Spreading

Freescale MC33781 is a master device for four differential DSI 2.02 buses.
MC33781 contains the logic to interface the buses to a standard serial
peripheral interface (SPI) port and the analog circuitry to drive data and power
over the bus, as well as receive data from the remote slave devices.

Freescale MC33781 Distributed System Interface (DSI) Master - Application Diagram

The differential mode of the MC 33781 generates lower electromagnetic
interference (EMI) in situations where data rates and wiring make this a
problem. Frequency spreading further reduces interference by spreading the
energy across many frequencies, reducing the energy in any single frequency.

Features of MC33781 DSI Master:

• Four independent differential DSI channels with a pseudo bus switch
  feature on channel 0
• Data rate up to 200kbps full duplex per channel
• Dual SPI (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; enables queuing of four
  independent slave commands at one time for each channel
• 8-bit to 16-bit messages with 0 to 8 bits of CRC
• Independent frequency spreading for each channel
• 32-Id SOICW exposed pad

MC33784 - DSI (Distributed System Interface) 2.02 Sensor Slave Interface

Freescale MC33784 is a slave, Distributed System Interface Bus (DBUS),
version 2.02 compatible device, optimized as a sensor interface. MC33784
contains circuits to power sensors such as accelerometers, and to digitize the
analog level from the sensor. MC33784 is controlled by commands over the bus,
and returns measured data and other information over the bus.

Freescale MC33784 DSI (Distributed System Interface) Slave - Application Diagram

Features of MC33784 DSI Sensor Slave:

• DSI version 2.02 compatible
• Sensor interface
  • 2-channel, 10-bit analog-to-digital converter
  • 3 pins configurable as logic inputs or outputs
  • Regulated 5V output  for sensor power from bus
• Bus interface
  • Single-ended or differential receiver
  • High- and low-side bus switches for improved common-mode noise rejection
  • 10MHz internal clock with dithering for improved EMI performance
  • DSI daisy chain device
• Fault modes
  • Under-voltage detection

Samples of the MC33781 and MC33784 DSI (Distributed System Interface) chips are available now.

References:

• http://www.freescale.com/files/pr/dsi.html (Freescale’s Distributed System
  Interface devices)
• http://www.freescale.com/files/analog/doc/data_sheet/MC33781.pdf
  (datasheet of MC33781 DSI Master)
• http://www.freescale.com/files/analog/doc/data_sheet/MC33784.pdf
  (datasheet of MC33784 DSI Slave)