HD74AC datasheet(13/52 Pages) HITACHI

13 / 52 page

FACT Descriptions and Family Characteristics

On FACT device data sheets, C

PD is a typical value and is given either for the package or for the individual

device (i.e., gates, flip-flops, etc.) within the package.

The circuit shown in Figure 9 was used to compare the power consumption of FACT versus ALS devices.

Two identical circuits were built on the same board and driven from the same input. In the circuit, the

input signal was driven into four D-type flip-flops which act as divide-by-2 frequency dividers. The

outputs from the flip-flops were connected to the inputs of a HD74AC138/74ALS138 decoder. This

generated eight non-overlapping clock pulses on the outputs of the HD74AC138/74ALS138, which were

then connected to an HD74AC04/74ALS04 inverter. The input frequency was then varied and the power

consumption was measured. Figure 10 illustrates the results of these measurements.

100

ALS

ALS Circuit

Stopped

Functioning

FACT

Frequency (MHz)

100

200

150

300

250

350

400

Figure 10 FACT vs ALS Circuit Power

Below 40 MHz, the FACT circuit dissipates much less power than the ALS version. It is interesting to note

that when the frequency went to zero, the FACT circuit’s power consumption also went to zero; the ALS

circuit continued to dissipate almost 100 mW. Another advantage of FACT is its capabilities above 40

MHz. At this frequency, the first 74ALS74 D-type flip-flop ceased to operate. Once this occurred, the

entire circuit stopped working and the power consumption fell to its quiescent value. The FACT device,

however, continued functioning beyond the limit of the frequency generator, which was 100 MHz.

This graph shows two advantages of FACT circuits (power and speed). FACT logic delivers increased

performance in addition to offering the power savings of CMOS.

HD74AC Datasheet(PDF) 13 Page - Hitachi Semiconductor