Texas Instruments CD74HCT245EG4

Overview

CD74HCT245EG4 from Texas Instruments is a high-speed CMOS octal bus transceiver with three-state non-inverting outputs, designed for bidirectional asynchronous data transfer between buses. It features 4.5 V to 5.5 V operation, 26 ns typical propagation delay (A↔B) at V_CC = 4.5 V, ±25 mA output drive, and -55°C to +125°C operating temperature range-enabling robust use in industrial control backplanes and legacy TTL-CMOS interface bridging.

For engineers reviewing the CD74HCT245EG4 datasheet, CD74HCT245EG4 pinout, CD74HCT245EG4 application, or CD74HCT245EG4 equivalent, key selection criteria include LSTTL-input compatibility (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V), three-state bus isolation timing (t_dis/t_en = 30/32 ns), and SOIC-20 package thermal performance (R_θJA = 58°C/W).

Technical Context

The CD74HCT245EG4 implements an 8-bit bidirectional bus transceiver controlled by a single direction (DIR) input and an active-low output enable (OE) signal. Its logic-level translation capability supports direct interfacing between 5 V LSTTL inputs and CMOS outputs without external level shifters.

All eight channels share identical electrical characteristics: symmetrical propagation delay (t_pd), matched transition times (t_t ≤ 15 ns), and tightly specified three-state leakage (I_OZ ≤ ±5 µA). The device operates only within its defined 4.5–5.5 V supply window and does not support dual-supply or mixed-voltage operation.

Key Specifications

Pinout & Package

CD74HCT245EG4 is packaged in a 20-pin SOIC (DW) with 12.80 mm × 7.50 mm body size and 1.27 mm lead pitch. The package is RoHS-compliant, moisture-sensitive level 1, and rated for peak reflow at 260°C.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT245N and 74ACT245SCX, CD74HCT245EG4 delivers the best balance of industrial temperature resilience, noise margin, and SOIC-20 thermal performance-making it the preferred choice for high-reliability 5 V bus bridging where layout density and long-term stability are prioritized over marginal speed gains.

Availability

CD74HCT245EG4 is available at Aetrix Electronics and suitable for industrial backplane interfaces, automotive ECU communication bridges, and legacy system bus extensions requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HCT245EG4 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 company headquartered in Dallas, Texas, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

CD74HCT245EG4 belongs to TI's CDx4HCT logic family, engineered specifically for robust 5 V bus interfacing in harsh-environment applications where LSTTL compatibility, wide temperature operation, and three-state isolation are mandatory design requirements.

FAQ

What is the maximum clock frequency supported by CD74HCT245EG4 in a synchronous bus application?

The CD74HCT245EG4 does not contain internal clocks or timing circuitry-it is a combinational transceiver. Its usable data rate depends on propagation delay (26 ns typ) and bus loading. For reliable operation with 50 pF load, the maximum sustainable toggle rate is approximately 15 MHz, assuming adequate setup/hold margins and clean edge transitions. Always verify timing against actual PCB trace capacitance and driver strength in the final design. CD74HCT245EG4 performance remains consistent across its full -55°C to +125°C range.

Can CD74HCT245EG4 operate with a 3.3 V supply voltage?

No. CD74HCT245EG4 is an HCT-type device specified only for 4.5 V to 5.5 V operation. Applying 3.3 V violates the recommended operating conditions and results in undefined logic behavior, increased propagation delay, and potential failure to recognize valid TTL input levels. For 3.3 V systems, consider ACT or LVC-family alternatives such as SN74LVC245A. CD74HCT245EG4 must be powered from a regulated 5 V rail to guarantee compliance with its V_IL/V_IH thresholds and output drive specifications.

How should unused input pins be handled on CD74HCT245EG4?

All unused inputs-including DIR, OE, and any unconnected A/B port pins-must be tied to a valid logic level (V_CC or GND) per TI's layout guidelines. Floating inputs cause increased ICC, erratic output states, and potential ESD susceptibility. For example, tie OE to V_CC to force high-impedance mode, or tie DIR to GND to fix A←B direction. Never leave inputs unconnected. This requirement applies identically across all operating temperatures and is essential for stable CD74HCT245EG4 functionality.

Is CD74HCT245EG4 pin-compatible with CD74HC245E?

Yes-CD74HCT245EG4 (SOIC-20) and CD74HC245E (PDIP-20) share identical pin numbering and functional mapping, but differ in logic family (HCT vs HC), supply range (4.5–5.5 V vs 2–6 V), and input compatibility (LSTTL vs CMOS). While pinout matches, substituting one for the other requires verifying V_CC, input source type, and timing margins. CD74HCT245EG4 is not a drop-in replacement for CD74HC245E in 3.3 V or mixed-voltage systems due to incompatible input thresholds.

What thermal considerations apply to CD74HCT245EG4 in high-density PCB layouts?

CD74HCT245EG4 in SOIC-20 has a junction-to-ambient thermal resistance (R_θJA) of 58°C/W. At maximum rated output current (±25 mA per pin across 8 channels), power dissipation can reach ~120 mW-raising junction temperature by ~7°C above ambient. To maintain reliability, ensure ≥1 cm² of copper pour connected to pin 10 (GND) and pin 19 (V_CC), place the 0.1 µF bypass capacitor within 5 mm of V_CC, and avoid stacking heat-generating components nearby. CD74HCT245EG4 thermal performance is validated only under JEDEC-standard board conditions.