HD74AC Datasheet, PDF (14/52 Pages) Hitachi Semiconductor – HD74AC Series Common Information

FACT Descriptions and Family Characteristics
2.2 Capacitive Loading Effects
In addition to temperature and power supply effects, capacitive loading effects for loads greater than 50 pF
should be taken into account for propagation delays of FACT devices. Minimum delay numbers may be
determined from table 3. Propagation delays are measured to the 50% point of the output waveform.
Table 3 Minimum Propagation Delay
Voltage(V)
Parameter
3.0
4.5
T_rise
31
22
t _fall
18
13
Note: TA = 25˚C
5.5
Units
19
ps/pF
12.5
ps/pF
The two graphs following, figures 11 and 12, describe propagation delays on FACT devices as affected by
variations in power supply voltage (V_CC) and lumped load capacitance (C_L). Figures 13 and 14 show the
effects of lumped load capacitance on rise and fall times for FACT devices.
Delay (ns)
32
30
28
26
C_{L = 1000 pF, tPLH}
24
22
20
18
16
C_L
C_L
=
=
1407000ppFF, _,tPtLPHHL
14
12
C_{L = 470 pF, tPHL}
10
8
C_{L = 220 pF, tPLH}
6
C_L = 220 pF, _tPHL
4
2
C_L = 50 pF, t_PHL
C_L = 50 pF, t_PLH
0
3.0
3.5
4.0
4.5
5.0
5.5
6.0
V_CC (Volts)
Figure 11 Propagation Delay vs. V_CC (HD74AC00)
13