Datasheet
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Typical Application
CANH
CANL
TMS470R1x MCU
SN65HVD251
D R
CANTX CANRX
TMS470R1x MCU
SN65HVD251
D R
GND
CANTX CANRX
TMS470R1x MCU
SN65HVD251
D R
CANTX CANRX
5 V
GND
5 V
GND
3.3 V
Stub Lines –– 0.3 m max
Bus Lines – 40 m max
120 W
V
ref
R
S
0.1 µF
V
CC
V
ref
R
S
V
CC
V
ref
R
S
0.1 µF 0.1 µF
V
CC
120 W
Sensor, Actuator, or
Control Equipment
Sensor, Actuator, or
Control Equipment
Sensor, Actuator, or
Control Equipment
SN65HVD251-Q1
SLLS788 – APRIL 2007
An eye pattern is a useful tool for measuring overall signal quality. As displayed in Figure 24 , 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 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 nearby electrical equipment.
The balanced receiver inputs of the HVD251 mitigate most sources of signal corruption, and when used with a
quality shielded twisted-pair cable, help ensure data integrity.
Figure 25. Typical HVD251 Application
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