
ProASIC3E DC and Switching Characteristics
2-50
Revision 13
Timing Characteristics
B-LVDS/M-LVDS
Bus LVDS (B-LVDS) and Multipoint LVDS (M-LVDS) specifications extend the existing LVDS standard to
high-performance multipoint bus applications. Multidrop and multipoint bus configurations may contain
any combination of drivers, receivers, and transceivers. Microsemi LVDS drivers provide the higher drive
current required by B-LVDS and M-LVDS to accommodate the loading. The drivers require series
terminations for better signal quality and to control voltage swing. Termination is also required at both
ends of the bus since the driver can be located anywhere on the bus. These configurations can be
implemented using the TRIBUF_LVDS and BIBUF_LVDS macros along with appropriate terminations.
Multipoint designs using Microsemi LVDS macros can achieve up to 200 MHz with a maximum of 20
loads. A sample application is given in
Figure 2-23. The input and output buffer delays are available in
Example: For a bus consisting of 20 equidistant loads, the following terminations provide the required
differential voltage, in worst-case Industrial operating conditions, at the farthest receiver: RS =60 and
RT =70 , given Z0 =50 (2") and Zstub =50 (~1.5").
Table 2-80 LVDS
Commercial-Case Conditions: TJ = 70°C, Worst-Case VCC = 1.425 V, Worst-Case
VCCI = 2.3 V
Speed Grade
tDOUT
tDP
tDIN
tPY
Units
Std.
0.66
1.87
0.04
1.82
ns
–1
0.56
1.59
0.04
1.55
ns
–2
0.49
1.40
0.03
1.36
ns
derating values.
Figure 2-23 B-LVDS/M-LVDS Multipoint Application Using LVDS I/O Buffers
...
RT
BIBUF_LVDS
R
+
-
T
+
-
R
+
-
T
+
-
D
+
-
EN
Receiver
Transceiver
Receiver
Transceiver
Driver
RS RS
Zstub
Z0