HD74AC datasheet(3/52 Pages) HITACHI

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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 (VCC) for two load capacitance values: 50

pF and stray capacitance. The clock frequency was 1 MHz for the measurements.

CL = 50 pF @ 1 MHz

CL = Fixture Capacitance

@ 1 MHz

VCC (Volts)

100

200

300

400

500

Figure 1 I

CC vs VCC

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

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