Datasheet

Analog Integrated Circuit Device Data
10 Freescale Semiconductor
33660
TYPICAL APPLICATIONS
INTRODUCTION
TYPICAL APPLICATIONS
INTRODUCTION
The 33660 is a serial link bus interface device conforming
to the ISO
9141 physical bus specification. The device is
designed for automotive environment usage, compliant with
On-board Diagnostics (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 33660
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 33660 is built
using Freescale Semiconductor’s SMARTMOS process and
is packaged in an 8-pin plastic SOIC.
FUNCTIONAL DESCRIPTION
The 33660 transforms 5.0 V microcontroller logic signals
to battery level logic signals and visa versa. The maximum
data rate is set by the rise and fall 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 33660
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 33660’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
 pull-up resistor and a diode to battery.
Reverse battery protection of the device is provided by the
use of a reverse battery blocking diode (See “D” in the Typical
Application Diagram on page 10). Battery line transient
protection of the device is provided for by using a 45 V zener
and a 500  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.
Figure 8. Typical Application Diagram
Components necessary for Reverse Battery (1), Overvoltage Transient (2), and 8.0 kV
ESD Protection (3) in a metal module case.
V
CC
D
x
SCIR
x
D
SCIT
x
D
MCU
VDD
CEN
RX
TX
VBB
ISO
GND
500 (2)
D(1)
ISO
K Line
510 
Service Scan Tool
or
End of Production Line
Programming
or
System Checking
T
x
D
R
x
D
+V
DD
= 5.0 V
45 V(2)
27 V(3)
5.0 nF(3)
33660
1.0 nF
10 nF(3)
+V
BAT
On-Board Diagnostic Link