onsemi 74VHCT245AMX

Overview

74VHCT245AMX from onsemi is an octal bus transceiver with 3-STATE outputs, designed for bidirectional asynchronous communication between data buses. It operates at 4.5–5.5 V, delivers 5.4 ns typical propagation delay, supports 8 mA output drive, and features power-down protection enabling safe 5 V ↔ 3 V level translation. Used in microcontroller peripheral expansion and memory bus isolation.

For engineers reviewing the 74VHCT245AMX datasheet, pinout, applications, or equivalent options, key selection criteria include bidirectional control via T/R input, OE-gated 3-STATE operation, ±25 mA output current capability, and guaranteed operation across −40°C to +85°C industrial temperature range.

Technical Context

The 74VHCT245AMX implements a dual-bus, direction-controlled transceiver architecture using silicon gate CMOS technology. Its T/R input selects data flow direction (A→B or B→A), while OE independently enables or disables all outputs into high-impedance state - supporting bus isolation without affecting internal logic states.

Input and output pins tolerate −0.5 V to +6.5 V regardless of VCC, enabling robust interfacing between mismatched supply domains. The device meets HBM ESD rating of 2000 V and complies with JEDEC MO-153 for TSSOP20 package mechanical dimensions.

Key Specifications

Pinout & Package

TSSOP20 (Case 948AQ), 4.4 mm × 6.5 mm footprint, 0.65 mm pitch, JEDEC MO-153 compliant surface-mount package with exposed thermal pad not present.

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 74VHCT245AMX uniquely balances 5 V system compatibility, 5.4 ns speed, and ±25 mA output drive - making it optimal for industrial bus isolation where mixed-voltage robustness and proven reliability are mandatory.

Availability

74VHCT245AMX is available at Aetrix Electronics and suitable for microcontroller bus expansion, memory interface isolation, and industrial I/O modules requiring stable component supply and long-term manufacturability.

Supply support for 74VHCT245AMX 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 74VHCT245AMX belongs to onsemi's VHCT logic family, engineered for high-speed, low-power bidirectional bus interfacing in industrial and embedded systems where 5 V compatibility and robust ESD protection are essential.

FAQ

What is the maximum operating frequency supported by the 74VHCT245AMX?

The 74VHCT245AMX does not specify a maximum clock frequency but supports data rates up to ~20 MHz in typical bus applications, based on its 5.4 ns typical propagation delay and 8.5 ns maximum tPLH/tPHL at CL = 50 pF. System-level timing must account for board trace delays and load capacitance; for 20 MHz operation, ensure total round-trip delay remains within one clock period. The 74VHCT245AMX is not a clocked device but a combinatorial transceiver, so frequency limits depend entirely on external timing constraints.

Is the 74VHCT245AMX pin-compatible with the older 74HCT245?

Yes, the 74VHCT245AMX is explicitly stated in its datasheet as pin and function compatible with the 74HCT245. Both share identical TSSOP20 pinout, truth table, and DC/AC electrical behavior. The 74VHCT245AMX improves upon the 74HCT245 with tighter propagation delay distribution, enhanced ESD robustness (2000 V HBM), and Pb-free packaging - making it a direct drop-in replacement in existing 74HCT245 designs.

Can the 74VHCT245AMX safely interface a 5 V microcontroller with a 3.3 V FPGA?

Yes, the 74VHCT245AMX can safely interface a 5 V microcontroller with a 3.3 V FPGA. Its inputs tolerate up to 6.5 V regardless of VCC, allowing direct connection of 5 V MCU outputs. When powered at 5 V, its outputs swing rail-to-rail (0 V/5 V), so a series resistor or external level shifter is required on outputs driving 3.3 V FPGA inputs to avoid overvoltage. For bidirectional use, configure the FPGA I/Os as 5 V tolerant or add discrete clamping.

What is the purpose of the T/R and OE pins on the 74VHCT245AMX?

The T/R (Transmit/Receive) pin controls data direction: LOW enables B→A transfer, HIGH enables A→B transfer. The OE (Output Enable) pin is active-low and globally disables all outputs into high-impedance state - isolating both A and B buses simultaneously. These two control signals operate independently: OE can override T/R to force tristate, while T/R determines direction only when OE is asserted. This dual-control scheme enables flexible bus arbitration in multiprocessor or DMA-based systems using the 74VHCT245AMX.

Does the 74VHCT245AMX require external pull-up or pull-down resistors on unused inputs?

Yes, per the datasheet's Recommended Operating Conditions, all unused inputs of the 74VHCT245AMX must be tied to a valid logic level - either VCC or GND - to prevent floating nodes that cause increased ICC, noise susceptibility, or erratic output behavior. Leaving inputs unconnected risks shoot-through current and violates the device's specified operating conditions. Unused outputs may be left open, but unused inputs must be terminated; this applies to OE, T/R, and any unused A/B port pins.