Philips Semiconductors Product data
AU5780ASAE/J1850/VPW transceiver
2001 Jun 19
4
PIN DESCRIPTION
SYMBOL PIN DESCRIPTION
BATT 1 Battery supply input (12V nom.)
TX 2 Transmit data input; low: transmitter passive; high: transmitter active
R/F 3 Rise/fall slew rate set input
RX 4 Receive data output; low: active bus condition detected; float/high: passive bus condition detected
BUS_IN 5 Bus line receive input
/LB 6 Loop-back test mode control input; low: loop-back mode; high: normal communication mode
BUS_OUT 7 Bus line transmit output
GND 8 Ground
FUNCTIONAL DESCRIPTION
The AU5780A 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
AU5780A 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 AU5780A 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 AU5780A 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 AU5780A 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 AU5780A
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 AU5780A 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.
The AU5780A is an enhanced successor of the AU5780. The
AU5780A provides improved wave shaping when exiting the low
power standby mode for reduced EMI. Several parameters that
were formerly only characterized to the maximum normal operating
supply of 16 volts, have now been characterized to 24 volt supplies.
These parameters which are tested and guaranteed to 24 volts are
identified with appropriate test conditions in the “conditions” columns
of the Characteristics tables, otherwise the conditions at the top of
the characteristic table applies to all parameters.
