Datasheet

SCBA015A
7–32
Fast GTLP Backplanes With the GTLPH1655
ERC = V
CC
, GND
V
CC
Signal Generator
With Different Edge Rates
Probe
V
TT
R
TT
= 25 Ω
Figure 22. Setup for Measuring Edge Rate at GTLP Side of SN74GTLPH1655
Additional measurement results on the SN74GTLPH1655 test board are presented in a later
section, which explains the behavior with a bus under realistic conditions.
The measurement results for falling edges are shown in Figures 23 and 24; Figures 25 and 26
show the curves for rising edges.
Using the definition of edge rate (slew rate) dV/dt = (V
OH
– V
OL
)/t
r
, t
f
, a slew rate results in
0.2 V/ns for slow edge rate (ERC = V
CC
) and 0.35 V/ns for fast edge rate (ERC = GND). As a
comparison, these values are significantly less than those of standard TTL devices, which are
usually about 1 V/ns, or more.
Input
Output
ERC = V
CC
4.00 V
3.00 V
2.00 V
1.00 V
0.00 V
–1.00 V
–2.00 V
5 ns 10 ns 15 ns 20 ns 25 ns 30 ns
Figure 23. Falling Edge, ERC = V
CC
(Slow Edges), Input Signals t
f
= 2 ns, 10 ns