HD74AC Datasheet, PDF (4/52 Pages) Hitachi Semiconductor – HD74AC Series Common Information

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–V_OL| / |V_IH–V_OH| at 4.5 V V_CC.
• FACT = 1.25/1.25 V
• ALS = 0.4/0.7 V
• LS = 0.3/0.7 V@ 4.75 V V_CC
• 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/I_OH Characteristics
• FACT = 24/–24 mA
• ALS = 24/–15 mA
• LS = 8/–0.4 mA @ 4.75 V V_CC
• HC = 4/–4 mA
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