Dictionary of Electronic Terms
"A"
"B"
"C",
"D",
"E",
"F",
"G",
"H",
"I",
"J",
"K",
"L",
"M",
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"Q",
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"S",
"T",
"U",
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"W",
"X",
"Y",
"Z"
74244 IC 8-Bit Buffer Chips
8-Bit Buffer Circuit
IC 8-Bit Buffer. used to drive data onto a 8-bit data bus. Note that the chip displayed indicates OE control of the output [Output Enable]. So the outputs could be taken tri-state if required. The functional IC is split into two 4-bit sections, so they could be operated together or separately, driving one 8-bit bus or two separate 4-bit buses.
Design Hint; Because this chip is used to drive a bus, which may be capacitive loaded, use more than the normal by-pass capacitor to insure that the IC has the current it needs when the buffers begin to drive the bus. Using just the standard .1uF capacitor may not be able to supply the required current fast enough to allow the 74244 to switch at the required speed. Also refer to Logic Family vs Switching Speed. The problem becomes more noticeable with faster logic families [a 74ACT244 switches faster than a 74HCT244 buffer]. Add a second by-pass capacitor, and place both by-pass capacitors as close to the Vcc line as possible.
20-pin Plastic SOP
These buffers are normally available in a number of package styles; however only the surface mount PSOP is shown. A Surface Mount Device [SMD] is always a better choice than a through-hole part, for a number of reasons. Other than size, Lead Inductance is the next important issue because it slows down switching time, while the size of the IC package causes the placement of the capacitor to move away from the power leads of the IC.
IC Buffer part numbers;
54ABT125; Quadruple Bus Buffer Gates, 3-State Outputs
54ALS241; Octal Buffers/Drivers With 3-State Outputs
74LCX245; Bidirectional Octal Buffers/Drivers With 3-State Outputs
74LCX244; Octal Buffers/Drivers, 5-volt tolerant CMOS
74ACT244; Octal Buffers/Drivers With 3-State Outputs
74ACT541; Octal Buffers/ Line Drivers
54ABT827; 10-Bit Buffers/Drivers With 3-State Outputs
74LVT2244; Octal Buffers/ Line Drivers
74LCX16244; Bidirectional Octal Buffers/Drivers, 3-State Outputs
74LCX16245; Bidirectional Octal Buffers/Drivers, 3-State Outputs
Not all families are shown above, just some examples; LCX, ABT, LVT and so on. The type or family of buffer used does make a difference in the table above, just the trailing digits that indicate the type of buffer [as in the different options]. Regardless of the family used, just be sure to provide by-pass next to the IC. Also, if possible run a larger trace to the IC or capacitor to insure the chip has the highest possible chance of getting the current it needs as fast as possible. The location of the bypass capacitor is extremely important; read more on Capacitor Placement, as it applies to IC by-passing.
74xx244 IC Buffers defined in DOD Vendor Item Drawings
V62/03607: 74HC244, Plastic small-outline
V62/03649: 74AHC244, Plastic small-outline
V62/03657: 74AHC244, Plastic small-outline
V62/03667: 74LVTH244A, Plastic small-outline
V62/04620: 74ACT244A, Plastic small-outline
V62/04622: 74AC244A, PSOP
V62/04622: 74LV244A, PSOP
Note the part number suffix is omitted. The suffix is used to define the package style [which is listed] and the packaging method during shipping [which is a don't care].
Also that the VIDs are valid [as of 6/15/2010], but there is no way to tell if the vendor defined in the document will produce these parts. Finally, note that the manufacturer is not listed here either. The point of this list is to indicate that a government agency could attempt to procure these items based on the VID number provided.
