AU5780 查看數據表（PDF） - Philips Electronics

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AU5780

SAE/J1850/VPW transceiver

Philips Electronics 

Philips Semiconductors

SAE/J1850/VPW transceiver

Product specification

AU5780

PIN DESCRIPTION

SYMBOL

PIN

BATT

1

TX

2

R/F

3

RX

4

BUS_IN

5

/LB

6

BUS_OUT

7

GND

8

DESCRIPTION

Battery supply input (12V nom.)

Transmit data input; low: transmitter passive; high: transmitter active

Rise/fall slew rate set input

Receive data output; low: active bus condition detected; float/high: passive bus condition detected

Bus line receive input

Loop-back test mode control input; low: loop-back mode; high: normal communication mode

Bus line transmit output

Ground

FUNCTIONAL DESCRIPTION

The AU5780 is an integrated line transceiver IC that interfaces an

SAE/J1850 protocol controller IC to the vehicle’s multiplexed bus

line. It is primarily intended for automotive “Class B” multiplexing

applications in passenger cars using VPW (Variable Pulse Width)

modulated signals with a nominal bit rate of 10.4 kbps. The AU5780

also receives messages in the so-called 4X mode where data is

transmitted with a typical bit rate of 41.6 kbps. The device provides

transmit and receive capability as well as protection to a J1850

electronic module.

A J1850 link controller feeds the transmit data stream to the

transceiver’s TX input. The AU5780 transceiver waveshapes the TX

data input signal with controlled rise & fall slew rates and rounded

shape. The bus output signal is transmitted with both voltage and

current control. The BUS_IN input is connected to the physical bus

line via an external resistor. The external resistor and an internal

capacitance provides filtering against RF bus noise. The incoming

signal is output at the RX pin being connected to the J1850 link

controller.

If the TX input is idle for a certain time, then the AU5780 enters a

low-power mode. This mode is dedicated to help meet ignition-off

current draw requirements. The BUS_IN input comparator is kept

alive in the low-power mode. Normal power mode will be entered

again upon detection of activity, i.e., rising edge at the TX input. The

device is able to receive and transmit a valid J1850 message when

initially in low-power mode.

The AU5780 features special robustness at its BATT and BUS_OUT

pins hence the device is well suited for applications in the

automotive environment. Specifically, the BATT input is protected

against 50V load dump, jump start and reverse battery condition.

The BUS_OUT output is protected against wiring fault conditions,

e.g., short circuit to battery voltage as well as typical automotive

transients (i.e., –200V / +200V). In addition, an overtemperature

shutdown function with hysteresis is incorporated which protects the

device under system fault conditions. The chip temperature is

sensed at the bus drive transistor in the output buffer. In case of the

chip temperature reaching the trip point, the AU5780 will latch-off

the transceiver function. The device is reset on the first rising edge

on the TX input after a small decrease of the chip temperature.

The AU5780 also provides a loop-back mode for diagnostic

purpose. If the /LB pin is open circuit or pulled low, then TX signal is

internally looped back to the RX output independent of the signals

on the bus. In this mode the electronic module is disconnected from

the bus, i.e., the TX signal is not output to the physical bus line. In

this mode, it can be used, e.g., for self-test purpose.

1998 Jun 30

4

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