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MC33290DR2

ISO K Line Serial Link Interface

Freescale Semiconductor 

TYPICAL APPLICATIONS

INTRODUCTION

TYPICAL APPLICATIONS

INTRODUCTION

The 33290 is a serial link bus interface device conforming

to the ISO 9141 physical bus specification. The device was

designed for automotive environment usage compliant with

On-Board Diagnostic (OBD) requirements set forth by the

California Air Resources Board (CARB) using the ISO K line.

The device does not incorporate an ISO L line. It provides bi-

directional half-duplex communications interfacing from a

microcontroller to the communication bus. The 33290

incorporates circuitry to interface the digital translations from

5.0 V microcontroller logic levels to battery level logic and

from battery level logic to 5.0 V logic levels. The 33290 is built

using Freescale Semiconductor’s SMARTMOS process and

is packaged in an 8-pin plastic SOIC.

FUNCTIONAL DESCRIPTION

The 33290 transforms 5.0 V microcontroller logic signals

to battery level logic signals and visa versa. The maximum

data rate is set by the fall time and the rise time. The fall time

is set by the output driver. The rise time is set by the bus

capacitance and the pull-up resistors on the bus. The fall time

of the 33290 allows data rates up to 150 kbps using a 30

percent maximum bit time transition value. The serial link

interface will remain fully functional over a battery voltage

range of 6.0 to 18 V. The device is parametrically specified

over a dynamic VBB voltage range of 8.0 to 18 V.

Required input levels from the microcontroller are ratio-

metric with the VDD voltage normally used to power the

microcontroller. This enhances the 33290’s ability to remain

in harmony with the RX and TX control input signals of the

microcontroller. The RX and TX control inputs are compatible

with standard 5.0 V CMOS circuitry. For fault-tolerant

purposes the TX input from the microcontroller has an internal

passive pull-up to VDD, while the CEN input has an internal

passive pull-down to ground.

A pull-up to battery is internally provided as well as an

active data pull-down. The internal active pull-down is

current-limit-protected against shorts to battery and further

protected by thermal shutdown. Typical applications have

reverse battery protection by the incorporation of an external

510 Ω pull-up resistor and diode to battery.

Reverse battery protection of the device is provided by

using a reverse battery blocking diode (“D” in the Simplified

Application Diagram on page 1). Battery line transient

protection of the device is provided for by using a 45 V zener

and a 500 Ω resistor connected to the VBB source as shown

in the same diagram. Device ESD protection from the

communication lines exiting the module is through the use of

the capacitor connected to the VBB device pin and the

capacitor used in conjunction with the 27 V zener connected

to the ISO pin.

Analog Integrated Circuit Device Data

Freescale Semiconductor

33290

9

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