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 V
BB
voltage range of 8.0 to 18 V.
Required input levels from the microcontroller are ratio-
metric with the V
DD
voltage normally used to power the
microcontroller. This enhances the 33290’s ability to remain
in harmony with the R
X
and T
X
control input signals of the
microcontroller. The R
X
and T
X
control inputs are compatible
with standard 5.0 V CMOS circuitry. For fault-tolerant
purposes the T
X
input from the microcontroller has an internal
passive pull-up to V
DD
, 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 V
BB
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 V
BB
device pin and the
capacitor used in conjunction with the 27 V zener connected
to the ISO pin.
33290
Analog Integrated Circuit Device Data
Freescale Semiconductor
9
FREESCALE [ FREESCALE SEMICONDUCTOR, INC ]
