Datasheet
7–199
Output Capacitance
GTL and BTL devices are designed to meet a 5-pF capacitance on their input and output ports (B port). Figure 10 shows the
variation of the output capacitance across both processes.
0
2
4
6
8
10
GTL GTL BTL BTL
B Port
Capacitance – pF
T
A
= 25°C, V
CC
= 5 V, V
IH
= 3 V, V
IL
= 0 V
All unused inputs are biased low
MINMIN MAX MAX
Figure 10. Capacitance Variation Across Process
Slew Rate
Slew rate plays an important role in backplane or point-to-point application designs. The slower the output slew rate of a device,
the less susceptible the signal is to reflections and noise. Using the backplane model (see Figures 1 and 2), the output slew rate
(t
r
and t
f
) of the driving device was taken under the following conditions: a 10-in., 50-Ω transmission line and a single termination
to V
TT
at the receiver end. Figures 11 through 14 show the rise and fall times of both devices taken between the two specified
voltages of 0.5 V to 1 V for GTL and 1.3 V to 1.8 V for BTL. Both the BTL and GTL slew rates are acceptable.