HD74AC datasheet(4/52 Pages) HITACHI

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FACT Descriptions and Family Characteristics

AC performance specifications are guaranteed at 5.0 V

± 0.5 V and 3.3 V ± 0.3 V. For worst case design at

2.0 V V

CC on all device types, the formula below can be used to determine AC performance.

AC performance at 2.0 V V

CC = 1.9 × AC specification at 3.3 V

1.5 Multiple Output Switching

Propagation delay is affected by the number of outputs switching simultaneously. Typically, devices with

more than one output will follow the rule: for each output switching, derate the databook specification by

250 ps. This effect typically is not significant on an octal device unless more than four outputs are

switching simultaneously. This derating is valid for the entire temperature range and 5.0 V

± 10% V

CC.

1.6 Noise Immunity

The noise immunity of a logic family is also an important equipment cost factor in terms of decoupling

components, power supply dynamic resistance and regulation as well as layout rules for PC boards and

signal cables.

The comparisons shown describe the difference between the input threshold of a device and the output

voltage, |V

IL–VOL| / |VIH–VOH| at 4.5 V VCC.

• FACT = 1.25/1.25 V

• ALS = 0.4/0.7 V

• LS = 0.3/0.7 V@ 4.75 V V

• HC = 1.25/1.25 V

1.7 Output Characteristics

All FACT outputs are buffered to ensure consistent output voltage and current specifications across the

family. Both HD74AC and HD74ACT device types have the same output structures. Two clamp diodes

are internally connected to the output pin to suppress voltage overshoot and undershoot in noisy system

applications witch can result from impedance mismatching. The balanced output design allows for

controlled edge rates and equal rise and fall times.

All devices (HD74AC or HD74ACT) are guaranteed to source and sink 24 mA. HD74AC/ACTXXX, are

capable of driving 50

Ω transmission lines.

1.7.1 I

OL/IOH Characteristics

• FACT = 24/–24 mA

• ALS = 24/–15 mA

• LS = 8/–0.4 mA @ 4.75 V V

• HC = 4/–4 mA

HD74AC Datasheet(PDF) 4 Page - Hitachi Semiconductor