onsemi 74F544SC

Overview

74F544SC from Fairchild Semiconductor is an octal registered transceiver with dual 8-bit D-type latch sets, separate A-to-B and B-to-A control paths (CEAB/LEAB/OEAB and CEBA/LEBA/OEBA), inverting data flow in both directions, A outputs rated for 24 mA sink, B outputs for 64 mA sink, and operates at +4.5V to +5.5V supply-used in bidirectional bus interfacing between microprocessor data buses and peripheral subsystems.

For engineers reviewing the 74F544SC datasheet, pinout, applications, or equivalent options, key selection criteria include 24-pin SOIC package compatibility, independent latch/output enable timing (tPLH/tPHL ≤ 10.5 ns), 3-STATE output drive asymmetry (A: 24 mA, B: 64 mA), and guaranteed operation across 0°C to +70°C ambient.

Technical Context

The 74F544SC implements two independent 8-bit register banks-A-to-B and B-to-A-each with dedicated latch enable (LEAB/LEBA) and output enable (OEAB/OEBA) inputs, allowing concurrent latching and 3-STATE control per direction. Data inversion occurs on both A→B and B→A paths, and each register bank supports transparent mode (LE = LOW) followed by storage (LE edge-triggered).

Control logic uses active-low enables: CEAB/CEBA govern data path activation, LEAB/LEBA control latch transparency vs. storage, and OEAB/OEBA determine 3-STATE buffer output state. Propagation delays are asymmetric-LEAB→Bn tPLH/tPHL up to 14.5 ns, while transparent-mode An→Bn delays are ≤10.5 ns-enabling precise timing coordination in synchronous bus systems.

Key Specifications

Pinout & Package

74F544SC is housed in a 24-lead Small Outline Integrated Circuit (SOIC) package per JEDEC MS-013, 0.300" wide, with gull-wing leads and standard pitch (1.27 mm). Pin numbering follows conventional SOIC orientation with Pin 1 marked by notch or dot.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal registered transceiver applications.

Compared with 74F544SC, SN74F544N offers identical functionality in through-hole form for ease of validation or repair, while 74F544MSA provides reduced footprint for high-density routing-neither is pin-compatible with 74F544SC due to differing package dimensions and lead pitch, requiring PCB redesign.

Availability

74F544SC is available at Aetrix Electronics and suitable for microprocessor bus interface, industrial PLC backplane, legacy system data bridge, and test equipment signal conditioning applications requiring stable component supply and long-term obsolescence management.

Supply support for 74F544SC includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Fairchild Semiconductor was a U.S.-based semiconductor company specializing in analog and mixed-signal ICs, power management, and logic devices before its acquisition by ON Semiconductor in 2016.

The 74F544SC belongs to Fairchild's 74F Fast TTL logic family, designed for high-speed, low-power registered data transfer in commercial-grade computing and industrial control systems.

FAQ

What is the primary function of the 74F544SC in a digital system?

The 74F544SC serves as an octal registered transceiver that enables bidirectional, latch-synchronized data transfer between two 8-bit buses. It contains two independent sets of D-type latches-one for A-to-B and one for B-to-A flow-with separate enable controls. The 74F544SC inverts data in both directions and provides asymmetric drive strength (24 mA on A outputs, 64 mA on B outputs), making it ideal for interfacing microprocessors with peripherals or bridging legacy subsystems where timing control and bus isolation are critical.

Does the 74F544SC support true bidirectional operation without external direction control logic?

Yes-the 74F544SC supports fully independent bidirectional operation using dedicated control inputs: CEAB/LEAB/OEAB manage A-to-B flow, while CEBA/LEBA/OEBA manage B-to-A flow. This eliminates the need for external direction-control logic or multiplexers. Each path operates autonomously, allowing simultaneous latching in one direction while outputting previously stored data in the other-enabling pipelined bus transactions in systems like microprocessor data buses or PLC backplanes.

What are the absolute maximum ratings for the 74F544SC supply and input voltages?

The 74F544SC has an absolute maximum VCC rating of −0.5V to +7.0V and input voltage range of −0.5V to +7.0V (with current limiting per Fairchild Note 2). Junction temperature must not exceed +150°C under bias, and storage temperature is rated from −65°C to +150°C. These limits define safe handling and operating boundaries-not functional specifications. For reliable operation, the 74F544SC must be used within recommended conditions: VCC = +4.5V to +5.5V and ambient temperature 0°C to +70°C.

How does the 74F544SC handle 3-STATE output leakage in high-impedance mode?

In 3-STATE (high-impedance) mode, the 74F544SC specifies I_OZL ≤ −650 µA at V_OUT = 0.5V and I_OZH ≤ 70 µA at V_OUT = 2.7V for both A and B terminals. These tightly bounded leakage values ensure minimal current draw and reliable bus isolation when outputs are disabled-critical for multi-drop bus architectures where multiple 74F544SC devices share signal lines. This performance is verified across the full commercial temperature range and supports robust contention-free bus sharing.

Is the 74F544SC pin-compatible with other 74F-series transceivers such as the 74F245?

No-the 74F544SC is not pin-compatible with the 74F245 or other octal transceivers. While both are 24-pin devices, the 74F544SC uses a unique pinout with dual independent control sets (CEAB/LEAB/OEAB and CEBA/LEBA/OEBA), whereas the 74F245 employs a single-direction control scheme (DIR, OE). The 74F544SC's pin assignment-including separate enables per direction and bi-directional I/O mapping-is specific to its registered transceiver architecture. Substituting it for a 74F245 would require complete PCB redesign and logic reimplementation.