HD74AC Datasheet, PDF (3/52 Pages) Hitachi Semiconductor – HD74AC Series Common Information

FACT Descriptions and Family Characteristics
1.3 Low Power CMOS Operation
If there is one single characteristic that justifies the existence of CMOS, it is low power dissipation. In the
quiescent state, FACT draws three orders of magnitude less power than the equivalent LS or ALS TTL
device. This enhances system reliability; because costly regulated high current power supplies, heat sinks
and fans are eliminated. FACT logic devices are ideal for portable systems such as laptop computers and
backpack communications systems. Operating power is also very low for FACT logic. Power
consumption of various technologies with a clock frequency of 1 MHz is shown below.
• FACT = 0.1 mW/gate
• ALS = 1.2 mW/gate
• LS = 2.0 mW/gate
• HC = 0.1 mW/gate
Figure 1 illustrates the effects of I_CC versus power supply voltage (V_CC) for two load capacitance values: 50
pF and stray capacitance. The clock frequency was 1 MHz for the measurements.
500
C_L = 50 pF @ 1 MHz
400
300
200
100
0
0
C_L = Fixture Capacitance
@ 1 MHz
2
4
6
V_CC (Volts)
Figure 1 I_CC vs V_CC
1.4 AC Performance
In comparison to LS, ALS and HC families, FACT devices have faster internal gate delays as well as the
basic gate delays. Additionally, as the level of integration increases, FACT logic leads the way to very
high-speed systems.
The example below describes typical values for a HD74XX138, 3 to 8 line decoder.
• FACT = 6.0 ns @ C_L = 50 pF
• ALS = 12.0 ns @ C_L = 50 pF
• LS = 27.0 ns @ C_L = 15 pF
• HC = 17.0 ns @ C_L = 50 pF
2