Datasheet

7–139
–100 –90 –80 –70 –60 –50 –40 –30 –20 –10 0
–100 –90 –80 –70 –60 –50 –40 –30 –20 –10 0
V
OH
– V
2.8
2
1.6
0.8
0
3.2
2.4
1.2
0.4
3.3-V Families
5-V Families
V
OH
– V
4
3.6
2.8
2
1.6
0.8
0
3.2
2.4
1.2
0.4
T
A
= 25°C,
V
CC
= 5 V,
V
IH
= 3 V,
V
IL
= 0 V
I
OH
– mA
I
OH
– mA
T
A
= 25°C,
V
CC
= 3.3 V,
V
IH
= 3 V,
V
IL
= 0 V
LVT2
LVC
ALVC
LVT
ABT
ABTE
ABT2
LV
Figure 9. Output-High Characteristic Impedance of 3.3-V and 5-V Families
Incident-Wave Switching
Incident-wave switching ensures that, for a given transition (either high-to-low or low-to-high), the output reaches a valid V
IH
or V
IL
level on the initial wave front (i.e., does not require reflections). Figure 10 shows potential problems a designer might
encounter when a device does not switch on the incident wave. A shelf below V
IL
(max)
,
signal A, causes the propagation delay
to slow by the amount of time it takes for the signal to reach the receiver and reflect back. Signal B shows the case where there
is a shelf in the threshold region. When this happens, the input to the receiver is uncertain and could cause several problems
associated with slow input edges, depending on the length of time the shelf remains in this region. Signal C will not cause a
problem because the shelf does not occur until the necessary V
IH
level has been attained.