Texas Instruments CD74HC243M

Overview

CD74HC243M from Texas Instruments is a high-speed CMOS quad-bus transceiver with three-state outputs, designed for bidirectional asynchronous data bus communication between A- and B-side ports. It operates from 2 V to 6 V, delivers 7 ns typical propagation delay (VCC = 5 V, CL = 15 pF), supports –55°C to +125°C industrial/military temperature range, and drives up to 15 LSTTL loads - used in backplane interface, memory expansion, and system-level bus isolation circuits.

For engineers reviewing the CD74HC243M datasheet, CD74HC243M pinout, CD74HC243M application, or CD74HC243M equivalent, this page provides verified functional mode logic, SOIC-14 package dimensions, HC-series voltage compatibility, three-state timing parameters, and validated alternative parts for bus transceiver selection in harsh-environment embedded systems.

Technical Context

The CD74HC243M implements four independent noninverting bidirectional channels, each controlled by dual active-low output-enable inputs (OEA, OEB) that jointly determine data direction (A→B or B→A) and high-impedance state. Its silicon-gate CMOS architecture ensures balanced rise/fall times and low dynamic power dissipation.

It features buffered inputs, fanout of 10 LSTTL loads on standard outputs and 15 on bus-driver outputs, and meets HC-series noise immunity specs (NIL/NIH = 30% of VCC at 5 V). Absolute maximum ratings include ±35 mA per output and 70 mA total supply current.

Key Specifications

Pinout & Package

CD74HC243M is housed in a 14-pin SOIC (D) package with nominal body size 8.65 mm × 3.90 mm and maximum height 1.75 mm. Pin 1 is located at the top-left corner with notch or beveled edge marking orientation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LVC243APW and CD74HCT243M, CD74HC243M offers the broadest supply range (2–6 V) and widest temperature rating (–55°C to +125°C), making it uniquely suitable for military, aerospace, and high-reliability industrial deployments where voltage margin and environmental robustness are critical.

Availability

CD74HC243M is available at Aetrix Electronics and suitable for industrial backplane interfaces, automotive ECU diagnostics ports, memory expansion subsystems, and legacy system bus bridges requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HC243M 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

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and logic solutions, with decades of heritage in high-reliability logic families and industrial-grade components.

CD74HC243M belongs to TI's CDx4HC logic portfolio, engineered for robust bidirectional bus communication in harsh environments - emphasizing wide voltage tolerance, extended temperature operation, and noise-immune CMOS design.

FAQ

What is the maximum clock frequency supported by CD74HC243M in a bus application?

CD74HC243M does not operate on a clock; it is a combinational transceiver. Its usable data rate depends on propagation delay and bus capacitance. With 7 ns typical tPD and 15 pF load, it reliably supports bidirectional bus toggling up to ~30 MHz in point-to-point configurations. For longer traces or higher capacitance, derating is required - always verify timing margins using tPLH/tPHL values from the datasheet for CD74HC243M.

Can CD74HC243M interface directly between 3.3 V and 5 V buses?

Yes. CD74HC243M supports 2 V to 6 V VCC, and its CMOS inputs accept VIH ≥ 3.15 V and VIL ≤ 1.35 V at VCC = 4.5 V - covering both 3.3 V logic-high and 5 V logic-low thresholds. When powered at 5 V, it safely receives 3.3 V inputs; when powered at 3.3 V, its outputs swing rail-to-rail and are compatible with 3.3 V receivers. Always confirm voltage translation direction and use appropriate pull-ups if needed for CD74HC243M.

What happens when both OEA and OEB are high on CD74HC243M?

When both OEA and OEB are high (logic 1), all eight I/O pins (A1–A4, B1–B4) enter high-impedance (three-state) mode - neither driving nor loading the connected buses. This condition prevents bus contention during system reset, power sequencing, or fault isolation. The truth table in the CD74HC243M datasheet explicitly defines this as the "Z" state for all ports, and TI recommends terminating unused I/Os with 10 kΩ–1 MΩ resistors to avoid floating nodes.

Is CD74HC243M pin-compatible with CD74HCT243M?

Yes - CD74HC243M and CD74HCT243M share identical SOIC-14 package dimensions, pin numbering, and pin functions. Both have NC on pins 13 and 14, and identical assignments for OEA, OEB, A1–A4, and B1–B4. However, they differ electrically: CD74HC243M uses CMOS input thresholds, while CD74HCT243M uses TTL-compatible thresholds. Swapping them requires verifying input voltage compatibility in the target system for CD74HC243M.

Does CD74HC243M require external pull-up or pull-down resistors on control inputs?

No - CD74HC243M has no internal weak pull-ups or pull-downs on OEA or OEB. These inputs must be actively driven to valid logic levels (0 V or VCC); leaving them floating risks metastability or unintended three-state activation. TI's layout guidelines mandate tying unused inputs to VCC or GND via discrete resistors. For CD74HC243M, OEA and OEB should be driven by clean digital signals or terminated with 10 kΩ resistors to avoid undefined behavior.