AN602

Vishay Siliconix

www.vishay.com

2

Document Number: 70573

16-Jan-01

TX

RXL

K

L

+

–

L

+

–

K

+

–

K

Logic Circuitry

(See State Diagram

and Truth Table)

GND

RXK

FIGURE 3. Si9243A K- and L-Line Driver

Since the fault detection signal is not brought out, it is up to the

user to determine if a fault has occurred. One method is to monitor

the RxK and TX lines and ensure they are in phase. An exclusive

OR can also perform the fault function.

The fault condition is cleared when TX is set high.

System Anomalies

Two system anomalies in the automotive environment that the

Si924x drivers may be subjected to are Reverse Battery and

Ground Disconnect.

protect the device from reverse battery conditions. This diode will

protect the IC to reverse batteries up to –24 V.

Signal and Communication Specifications

ISO 9141 specifies different logic levels for the Receiver and

Transmitter.

Receiver Logic Levels:

Logic “0”

Transmitter Logic Levels:

Logic “0”

The Vishay Siliconix drivers operate to the above specifications,

but with a slightly tighter transmission requirement: Logic “1”

minimum

A logic bit transition must be less than 10% of the total bit time.

The transition time is measured between the 80% and 20%

battery points. Bit time is defined as the time between the 50%

battery points of consecutive rising and falling levels.

FIGURE 4. Si9243EY Applications Circuit

Regulator

GND

Logic Circuitry

Micro

Processor

Car

Battery

RXL

RXK

TX

K

GND

Si9243

K-Line

L-Line

BUS

510

W

Diagnostic Tester

5 V