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7400 series

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7400 series

The 7400 series of transistor–transistor logic (TTL) integrated circuits are the most popular family of TTL integrated circuit logic. Quickly replacing diode–transistor logic, it was used to build the mini and mainframe computers of the 1960s and 1970s. Several generations of pin-compatible descendants of the original family have since become de facto standard electronic components.



The 7400 series contains hundreds of devices that provide everything from basic logic gates, flip-flops, and counters, to special purpose bus transceivers and arithmetic logic units (ALU). Specific functions are described in a list of 7400 series integrated circuits.

Today, surface-mounted CMOS versions of the 7400 series are used in various applications in electronics and for glue logic in computers and industrial electronics. The original through-hole devices in dual in-line packages (DIP/DIL), which were the mainstay of the industry for many decades, are very useful for rapid breadboard-prototyping and education and so remain available from most manufacturers. The fastest types and very low voltage versions are typically surface-mount only, however.

The first part number in the series, the 7400, designates a device containing four two-input NAND gates. Each gate uses two pins for input and one pin for its output, and the remaining two contacts supply power (+5 V) and connect the ground. This part was made in various packages including flat pack, plastic or ceramic dual in-line packages with 14 pins, and in surface mount packages as well. Additional numbers and letters in a full part number identify the package and other variations.

While designed as a family of digital logic, some TTL chips were used in analog circuits like Schmitt triggers. Like the 4000 series, the newer CMOS versions of the 7400 series are also usable as analog amplifiers using negative feedback (similar to operational amplifiers with only an inverting input).

7400 series derivative families

7400 series parts were constructed using bipolar transistors, forming what is referred to as transistor–transistor logic or TTL. Newer series, more or less compatible in function and logic level with the original parts, use CMOS technology or a combination of the two (BiCMOS). Originally the bipolar circuits provided higher speed but consumed more power than the competing 4000 series of CMOS devices. Bipolar devices are also limited to a fixed power supply voltage, typically 5 V, while CMOS parts often support a range of supply voltages.

Milspec-rated devices for use in extended temperature conditions are available as the 5400 series. Texas Instruments also manufactured radiation-hardened devices with the prefix RSN, and the company offered beam-lead bare dies for integration into hybrid circuits with a BL prefix designation.

Regular-speed TTL parts were also available for a time in the 6400 series – these had an extended industrial temperature range of −40 °C to +85 °C. While companies such as Mullard listed 6400-series compatible parts in 1970 data sheets, by 1973 there was no mention of the 6400 family in the Texas Instruments TTL Data Book. Some companies have also offered industrial extended temperature range variants using the regular 7400 series part numbers with a prefix or suffix to indicate the temperature grade.

As integrated circuits in the 7400 series were made in different technologies, usually compatibility was retained with the original TTL logic levels and power supply voltages. An integrated circuit made in CMOS is not a TTL chip, since it uses field-effect transistors (FETs) and not bipolar junction transistors, but similar part numbers are retained to identify similar logic functions and electrical (power and I/O voltage) compatibility in the different subfamilies. Over 40 different logic subfamilies use this standardized part number scheme.

  • Bipolar
  • 74 – Standard TTL. the original logic family had no letters between the "74" and the part number. 10 ns gate delay, 10 mW dissipation, 4.75–5.25 V, released in 1966.
  • 74L – Low-power. Larger resistors allowed 1 mW dissipation at the cost of a very slow 33 ns gate delay. Obsolete, replaced by 74LS or CMOS technology. Introduced 1971.
  • 74H – High-speed. 6 ns gate delay but 22 mW power dissipation. Used in 1970s era supercomputers. Still produced but generally superseded by the 74S series. Introduced in 1971.
  • 74S – High-speed Schottky. Implemented with Schottky diode clamps at the inputs to prevent charge storage, this provides faster operation than the 74 and 74H series at the cost of increased power consumption and cost. 3 ns gate delay, 20 mW dissipation, released in 1971.
  • 74LS – Low-power Schottky. Implemented using the same technology as 74S but with reduced power consumption and switching speed. Typical 10 ns gate delay, a remarkable (for the time) 2 mW dissipation, 4.75–5.25 V.
  • 74AS – Advanced Schottky, the next iteration of the 74S series with greater speed and fan-out despite lower power consumption. Implemented using the 74S's technology with "miller killer" circuitry to speed up the low-to-high transition. 1.7 ns gate delay, 8 mW, 4.5–5.5 V.
  • 74ALS – Advanced low-power Schottky. Same technology as 74AS but with the speed/power tradeoff of the 74LS. 4 ns, 1.2 mW, 4.5–5.5 V.
  • 74F – Fast. Fairchild's version of TI's 74AS. 3.4 ns, 6 mW, 4.5–5.5 V. Introduced in 1978.
  • CMOS
  • C – CMOS 4–15 V operation similar to buffered 4000 (4000B) series.
  • HC – High-speed CMOS, similar performance to LS, 12 ns. 2.0–6.0 V.
  • HCT – High speed, compatible logic levels to bipolar parts.
  • AC – Advanced CMOS, performance generally between S and F.
  • ACQ – Advanced CMOS with Quiet outputs.
  • AHC – Advanced high-speed CMOS, three times as fast as HC, tolerant of 5.5V on input.
  • ALVC – Low-voltage – 1.8–3.3 V, time Propagation Delay (TPD) < 3 ns at 3.3 V.
  • ALVT – Low-voltage – 2.5–3.3 V, 5 V tolerant inputs, high current ≤ 64 mA, TPD < 3 ns at 2.5 V.
  • AUC – Low-voltage – 0.8–2.5 V, TPD < 2.5 ns at 1.8 V.
  • AUP – Low-voltage – 0.8–3.6 V (3.3 V typically), TPD 15.6/8.2/4.3 ns at 1.2/1.8/3.3V, partial power-down specified (IOFF), inputs protected.
  • AVC – Low-voltage – 1.8–3.3 V, TPD < 3.2 ns at 1.8 V, bus hold, IOFF.
  • FC – Fast CMOS, performance similar to F.
  • LCX – CMOS with 3 V supply and 5 V tolerant inputs.
  • LV – Low-voltage CMOS – 2.0–5.5 V supply and 5 V tolerant inputs.
  • LVC – Low voltage – 1.65–3.3 V and 5 V tolerant inputs, TPD < 5.5 ns at 3.3 V, TPD < 9 ns at 2.5 V.
  • LV-A – 2.5–5 V, 5 V tolerant inputs, TPD < 10 ns at 3.3 V, bus hold, IOFF, low noise.
  • LVT – Low-voltage – 3.3 V supply, 5 V tolerant inputs, high output current < 64 mA, TPD < 3.5 ns at 3.3 V, IOFF, low noise.
  • LVQ – Low-voltage – 3.3 V.
  • LVX – Low-voltage – 3.3 V with 5 V tolerant inputs.
  • VHC – Very-high-speed CMOS – "S" performance in CMOS technology and power.
  • BiCMOS
  • BCT – BiCMOS, TTL-compatible input thresholds, used for buffers.
  • ABT – Advanced BiCMOS, TTL-compatible input thresholds, faster than ACT and BCT.
  • Many parts in the CMOS HC, AC, and FC families are also offered in "T" versions (HCT, ACT, and FCT) which have input thresholds that are compatible with both TTL and 3.3 V CMOS signals. The non-T parts have conventional CMOS input thresholds.

    The 74H family is the same basic design as the 7400 family with resistor values reduced. This reduced the typical propagation delay from 9 ns to 6 ns but increased the power consumption. The 74H family provided a number of unique devices for CPU designs in the 1970s. Many designers of military and aerospace equipment used this family over a long period and as they need exact replacements, this family is still produced by Lansdale Semiconductor.

    The 74S family, using Schottky circuitry, uses more power than the 74, but is faster. The 74LS family of ICs is a lower-power version of the 74S family, with slightly higher speed but lower power dissipation than the original 74 family; it became the most popular variant once it was widely available.

    The 74F family was introduced by Fairchild Semiconductor and adopted by other manufacturers; it is faster than the 74, 74LS and 74S families.

    Through the late 1980s and 1990s newer versions of this family were introduced to support the lower operating voltages used in newer CPU devices.


    Although the 7400 series was the first de facto industry standard TTL logic family (i.e. second-sourced by several semiconductor companies), there were earlier TTL logic families such as the Sylvania SUHL (Sylvania Universal High-level Logic) family, Motorola MC4000 MTTL family (not to be confused with RCA CD4000 CMOS), the National Semiconductor DM8000 family, Fairchild 9300 series, and the Signetics 8200 and 8T00 family.

    The 7400N quad NAND gate was the first product in the series, introduced by Texas Instruments in a military grade metal flat package in October 1964. The extremely popular commercial grade plastic DIP followed in the third quarter of 1966.

    The 5400 and 7400 series were used in many popular minicomputers in the 1970s and early 1980s. Some models of the DEC PDP series 'minis' used the 74181 ALU as the main computing element in the CPU. Other examples were the Data General Nova series and Hewlett-Packard 21MX, 1000, and 3000 series.

    Hobbyists and students equipped with wire wrap tools, a 'breadboard' and a 5-volt power supply could also experiment with digital logic referring to how-to articles in Byte magazine and Popular Electronics which featured circuit examples in nearly every issue. In the early days of large-scale IC development, a prototype of a new large-scale integrated circuit might have been developed using TTL chips on several circuit boards, before committing to manufacture of the target device in IC form. This allowed simulation of the finished product and testing of the logic before the availability of software simulations of integrated circuits.

    In 1965, typical quantity-one pricing for the SN5400 (military grade, in ceramic welded flat-pack) was around 22 USD. As of 2007, individual commercial-grade chips in molded epoxy (plastic) packages can be purchased for approximately 0.25 USD each, depending on the particular chip.

    Part numbering scheme

    The part numbers for 7400 series logic devices often use the following naming convention, though specifics vary between manufacturers.

  • First, although sometimes omitted, a two or three letter prefix which indicates the manufacturer of the device (e.g. SN for Texas Instruments, DM for National Semiconductor), although these codes are no longer closely associated with a single manufacturer. For example, Fairchild Semiconductor manufactures parts with MM and DM prefixes, and no prefixes.
  • Two digits, where "74" indicates a commercial temperature range device and "54" indicates a military temperature range. Historically: "64" indicated a short-lived series with an intermediate "industrial" temperature range.
  • Up to four letters describing the logic subfamily, as listed above (e.g. "LS" or "HCT").
  • Two or more digits assigned for each device, e.g. 00 for a quad 2-input NAND gate. There are hundreds of different devices in each family. The allocation of device numbers (and, with a few exceptions, the pin-outs) of the original 7400 family was carried across to the later families, and new numbers allocated for new functions, plus some of the competing CD4000 numbers and pin-outs were included over time. There is no pattern to the allocation of these numbers. The function and pin-out of the chip is nearly always the same for the same device number regardless of subfamily manufacturer – exceptions are discussed below.
  • Additional suffix letters and numbers may be attached to indicate the package type, quality grade, or other information, but this varies widely by manufacturer.
  • For example, SN74ALS245N means this is a device probably made by Texas Instruments (SN), it is a commercial temperature range TTL device (74), it is a member of the "advanced low-power Schottky" family (ALS), and it is a bi-directional eight-bit buffer (245) in a plastic through-hole DIP package (N).

    Many logic families maintain a consistent use of the device numbers as an aid to designers. Often a part from a different 74x00 subfamily could be substituted ("drop-in replacement") in a circuit, with the same function and pin-out yet more appropriate characteristics for an application (perhaps speed or power consumption), which was a large part of the appeal of the 74C00 series over the competing CD4000B series, for example. But there are a few exceptions where incompatibilities (mainly in pin-out) across the subfamilies occurred, such as:

  • some flat-pack devices (e.g. 7400W) and surface-mount devices,
  • some of the faster CMOS series (for example 74AC),
  • a few low-power TTL devices (e.g. 74L86, 74L9 and 74L95) have a different pin-out than the regular (or even 74LS) series part.
  • five versions of the 74x54 (4-wide AND-OR-INVERT gates IC), namely 7454(N), 7454W, 74H54, 74L54W and 74L54N/74LS54, are different from each other in pin-out and/or function,
  • References

    7400 series Wikipedia

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