Datasheet
SCEA019 - January 2001
7–92 Texas Instruments GTLP Frequently Asked Questions
Lumped loads normally are associated with point-to-point applications. However, GTLP
devices have been designed into actual backplane netlists and a resistance/inductance/
capacitance (RLC) network that closely matches the results in a backplane. TI’s GTLP
devices are tested into a lumped load, as are all other devices offered by TI and other
semiconductor manufacturers. Engineers are using GTLP devices in high-performance
distributed-capacitance loads and the actual switching characteristics are radically different
from the lumped loads that are specified in the data sheet. TI SPICE-modeled values using
the RLC network are included in the data sheet to better help engineers understand
backplane effects. In summary, the data-sheet switching-characteristics into the lumped-load
parameter values are going to look ugly but the actual performance of the device in a
distributed load is going to be beautiful.
12 What is the difference between GTLP and LVDS?
GTLP is a single-ended low-voltage-swing (<1 V) standard, whereas LVDS is a differential
low-voltage-swing (350 mV, typical) standard. Single-ended devices require only one trace per
bit of data, while differential devices require two traces for each bit of data. Differential
devices, e.g., LVDS, LVDM (backplane optimized LVDS), SERDES, Wizard, etc., work well for
high-speed data transmission over long cables, such as between cabinets, cards, or racks, as
shown in Figure 11, but they do not fit all applications where simplicity and lower cost of
implementation indicate that single-ended devices are better for use in multislot backplane
applications.
Between
Racks
Backplane
Connection
Between
Cabinets
Between
Cards
On the
Backplane
Figure 11. Various Equipment Connections