Datasheet

75% SAMPLE POINT
500 mV Threshold
900 mV Threshold
ALLOWABLE JITTER
NOISE MARGIN
NOISE MARGIN
RECEIVER DETECTION WINDOW
W
120
W
120
CANH
CANL
TMS320LF243
SN65HVD1040
D R
STB
SPLIT
CANTX CANRX
Sensor, Actuator, or Control
Equipment
TMS320LF243
D R
0.1mF
Vcc
GND
STB
CANTX CANRX
Sensor, Actuator, or Control
Equipment
TMS320LF2407A
SN65HVD230
D R
Rs
Vref
CANTX CANRX
Sensor, Actuator, or Control
Equipment
5 V
0.1mF
Vcc
GND
5 V
0.1mF
Vcc
GND
3.3 V
Stub Lines -- 0.3 m max
Bus Lines -- 40 m max
SN65HVD1040
SPLIT
SN65HVD1040
www.ti.com ............................................................................................................................................... SLLS631D – MARCH 2007 – REVISED DECEMBER 2008
Figure 24. Typical CAN Differential Signal Eye-Pattern
An eye pattern is a useful tool for measuring overall signal quality. As displayed in Figure 25 , the differential
signal changes logic states in two places on the display, producing an “ eye. ” Instead of viewing only one logic
crossing on the scope, an entire “ bit ” of data is brought into view. The resulting eye pattern includes all of the
effects of systemic and random distortion, and displays the time during which a signal may be considered valid.
The height of the eye above or below the receiver threshold voltage level at the sampling point is the noise
margin of the system. Jitter is typically measured at the differential voltage zero-crossing during the logic state
transition of a signal. Note that jitter present at the receiver threshold voltage level is considered by some to be a
more effective representation of the jitter at the input of a receiver.
As the sum of skew and noise increases, the eye closes and data is corrupted. Closing the width decreases the
time available for accurate sampling, and lowering the height enters the 900 mV or 500 mV threshold of a
receiver.
Different sources induce noise onto a signal. The more obvious noise sources are the components of a
transmission circuit themselves; the signal transmitter, traces and cables, connectors, and the receiver. Beyond
that, there is a termination dependency, cross-talk from clock traces and other proximity effects, V
CC
and ground
bounce, and electromagnetic interference from near-by electrical equipment.
The balanced receiver inputs of the HVD1040 mitigate most all sources of signal corruption, and when used with
a quality shielded twisted-pair cable, help insure data integrity.
Figure 25. Typical HVD1040 Application
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