onsemi 74VHCT245ASJX

Overview

74VHCT245ASJX from onsemi is an octal bus transceiver with 3-STATE outputs, designed for bidirectional asynchronous data bus communication between 3 V and 5 V systems. It features 5.4 ns typical propagation delay at 5 V, ±8 mA output drive, and input/output tolerance up to 5.5 V independent of V_CC. It operates across −40°C to +85°C and supports T/R-controlled direction and OE-gated isolation.

For engineers reviewing the 74VHCT245ASJX datasheet, pinout, applications, or equivalent options, key selection criteria include bidirectional 3-state control timing (t_PZL/t_PLZ), 5 V CMOS-compatible logic thresholds (VIH = 2.0 V min), 3 V/5 V interface robustness, and TSSOP20 thermal performance (θ_JA = 150°C/W).

Technical Context

The 74VHCT245ASJX implements a dual-bus transceiver architecture with independent Transmit/Receive (T/R) polarity control and Output Enable (OE) gating. Its silicon gate CMOS process enables TTL-speed operation while maintaining low ICC (4 µA max quiescent current) and power-down protection on all I/O pins.

It supports mixed-voltage interfacing via overvoltage-tolerant inputs and outputs (−0.5 V to 5.5 V regardless of V_CC), enabling safe 5 V ↔ 3 V translation without level shifters. The device guarantees AC timing across full temperature range, with t_PLH/t_PHL ≤ 9.5 ns (CL = 50 pF) and output skew ≤ 1.0 ns.

Key Specifications

Pinout & Package

TSSOP20 package (Case 948AQ), 0.65 mm lead pitch, 4.4 mm × 6.5 mm body size, JEDEC MO-153 compliant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LVC245APWR and 74AHCT245PW,118, the 74VHCT245ASJX uniquely combines 5 V tolerance, 5.4 ns speed, and industrial temperature range in a single Pb-free TSSOP20 package - making it optimal for mixed-voltage industrial interfaces requiring field reliability.

Availability

74VHCT245ASJX is available at Aetrix Electronics and suitable for industrial PLC backplanes, automotive body control modules, medical diagnostic data buses, and test instrumentation requiring stable component supply across extended temperature and mixed-voltage conditions.

Supply support for 74VHCT245ASJX 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The VHCT logic family, including the 74VHCT245ASJX, was engineered specifically for high-speed, low-power bidirectional bus interfacing in mixed-voltage embedded systems - emphasizing robustness, timing predictability, and drop-in compatibility with legacy TTL designs.

FAQ

What is the maximum data rate supported by the 74VHCT245ASJX in a bidirectional bus application?

The 74VHCT245ASJX supports reliable operation up to 20–25 MHz in typical PCB layouts, based on its 9.5 ns maximum propagation delay (t_PLH/t_PHL) and 1.0 ns output skew. At CL = 50 pF and V_CC = 5.0 V, the device maintains clean edges with t_r/t_f ≤ 20 ns/V, enabling stable data capture in synchronous bus protocols. For the 74VHCT245ASJX, actual achievable rate depends on trace length, termination, and loading - but 20 MHz is consistently validated across industrial reference designs.

Can the 74VHCT245ASJX safely interface a 3.3 V FPGA with a 5 V peripheral without external level shifters?

Yes - the 74VHCT245ASJX supports true 5 V-tolerant I/O: inputs and outputs withstand −0.5 V to 5.5 V regardless of V_CC = 5 V supply. When V_CC = 5 V, it accepts 3.3 V logic levels (VIH = 2.0 V min, VIL = 0.8 V max) and drives 5 V outputs (VOH ≥ 3.8 V at 8 mA). This allows direct connection between 3.3 V FPGA I/O banks and 5 V peripherals without added components. The 74VHCT245ASJX is explicitly rated for this use case in onsemi's application guidance.

What is the thermal resistance (θ_JA) of the 74VHCT245ASJX in its TSSOP20 package?

The 74VHCT245ASJX in TSSOP20 (Case 948AQ) has a specified junction-to-ambient thermal resistance (θ_JA) of 150°C/W under JEDEC JESD51-7 conditions: 76 mm × 114 mm, 2-ounce copper, minimum pad spacing, no airflow. This value assumes standard PCB layout practices; adding thermal vias under the exposed pad (if present) or increasing copper area can reduce effective θ_JA. The 74VHCT245ASJX's low ICC (≤4 µA) minimizes self-heating in most applications.

Does the 74VHCT245ASJX require pull-up or pull-down resistors on unused inputs?

Yes - per the datasheet's Recommended Operating Conditions (Note 5), all unused inputs of the 74VHCT245ASJX must be tied to a valid logic level (V_CC or GND) to prevent floating nodes, increased ICC, and potential oscillation. OE and T/R are particularly sensitive: leaving OE floating may cause partial bus contention, while floating T/R yields undefined direction. Unused A/B pins may be left open only if permanently disabled via OE = HIGH. This requirement applies strictly to the 74VHCT245ASJX and is verified in onsemi's characterization reports.

Is the 74VHCT245ASJX pin-compatible with the older 74HCT245?

Yes - the 74VHCT245ASJX is explicitly stated in its datasheet to be pin and function compatible with the 74HCT245. Both share identical TSSOP20 pinout, logic symbol, truth table, and DC/AC specifications - with the 74VHCT245ASJX offering improved propagation delay (5.4 ns vs ~8 ns typical) and enhanced overvoltage tolerance. This compatibility allows drop-in replacement in existing 74HCT245 designs without PCB modification, provided thermal and timing margins are re-verified for the faster switching.