Datasheet

10
0.1
1M
Data Rate - Hz
1
100k 10M 100M
100
Transmission Distance - m
1000
5% Jitter
30% Jitter
24 AWG UTP 96 Ω (PVC Dielectric)
FAIL SAFE
Rt = 100 Ω (Typ)
300 kΩ 300 kΩ
V
CC
V
IT
≈ 2.3 V
A
B
Y
SN65LVDM179 , SN65LVDM180
SN65LVDM050 , SN65LVDM051
www.ti.com .................................................................................................................................................... SLLS324J – DECEMBER 1998 – REVISED JULY 2009
The devices are generally used as building blocks for high-speed point-to-point data transmission. Ground
differences are less than 1 V with a low common-mode output and balanced interface for low noise emissions.
Devices can interoperate with RS-422, PECL, and IEEE-P1596. Drivers/receivers maintain ECL speeds without
the power and dual supply requirements.
Figure 21. Data Transmission Distance Versus Rate
One of the most common problems with differential signaling applications is how the system responds when no
differential voltage is present on the signal pair. The LVDS receiver is like most differential line receivers, in that
its output logic state can be indeterminate when the differential input voltage is between – 50 mV and 50 mV and
within its recommended input common-mode voltage range. TI's LVDS receiver is different; however, in the way
it handles the open-input circuit situation.
Open-circuit means that there is little or no input current to the receiver from the data line itself. This could be
when the driver is in a high-impedance state or the cable is disconnected. When this occurs, the LVDS receiver
pulls each line of the signal pair to near V
CC
through 300-k Ω resistors as shown in Figure 22 . The fail-safe
feature uses an AND gate with input voltage thresholds at about 2.3 V to V
CC
– 0.4 V to detect this condition and
force the output to a high-level, regardless of the differential input voltage.
Figure 22. Open-Circuit Fail Safe of the LVDS Receiver
It is only under these conditions that the output of the receiver is valid with less than a 50-mV differential input
voltage magnitude. The presence of the termination resistor, R
t
, does not affect the fail-safe function as long as it
is connected as shown in the figure. Other termination circuits may allow a dc current to ground that could defeat
the pullup currents from the receiver and the fail-safe feature.
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Product Folder Link(s): SN65LVDM179 SN65LVDM180 SN65LVDM050 SN65LVDM051