onsemi MC74ACT646NG

Overview

MC74ACT646NG from onsemi is an octal registered bus transceiver with 3-state outputs and non-inverting data paths, implementing dual-directional real-time and registered data transfer between A and B buses. It features independent A/B registers, TTL-compatible inputs, 24 mA output drive, and operates at 4.5–5.5 V supply. Used in synchronous bus interface applications requiring data latching and direction-controlled bidirectional flow.

For engineers reviewing the MC74ACT646NG datasheet, pinout, applications, or equivalent options, key selection considerations include clock-controlled register loading (CAB/CBA), dual transmit/receive control (SAB/SBA), output enable logic (G/DIR), and SOIC-24 package compatibility with industrial bus backplanes.

Technical Context

The MC74ACT646NG integrates eight D-type flip-flops per bus side, enabling simultaneous storage of A0–A7 and B0–B7 data on LOW-to-HIGH clock transitions at CAB or CBA. Its control architecture supports four distinct data-handling modes-real-time A→B, real-time B→A, stored A→B, and stored B→A-determined by SAB, SBA, DIR, and G inputs.

Logic operation relies on two independent 3-state output enable paths: G (global output disable) and DIR (direction select), where DIR = L enables B→A transfer and DIR = H enables A→B transfer. All outputs are TTL-compatible and capable of sourcing/sinking ±24 mA under VCC = 5.0 V, with propagation delays as low as 2.5 ns (tPLH, bus-to-bus) at 5 V.

Key Specifications

Pinout & Package

MC74ACT646NG is housed in a 24-pin SOIC wide-body (SOIC-24 WB) package per case 751E, with 300 mil width, Pb-free finish (G suffix), and JEDEC-standard pin layout.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ACT646N and 74LVTH16646DL, the MC74ACT646NG offers tighter DC output voltage specs (VOL = 0.44 V max at 24 mA), lower quiescent current (80 μA), and guaranteed MSL Level 1 handling-making it preferred for space-constrained industrial modules requiring long-term solderability assurance.

Availability

MC74ACT646NG is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy microcontroller bus extensions, and automated test equipment requiring stable component supply, long-lifecycle support, and RoHS-compliant packaging.

Supply support for MC74ACT646NG 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 focused on energy-efficient innovation across automotive, industrial, cloud, and intelligent power solutions.

The MC74ACT646NG belongs to the ACT logic family, designed specifically for high-speed, low-noise 5 V digital bus interfacing with robust noise immunity and precise timing control in mission-critical embedded systems.

FAQ

What is the maximum clock frequency supported by the MC74ACT646NG?

The MC74ACT646NG does not specify a maximum clock frequency in its datasheet; instead, timing is defined by minimum pulse width (tw = 7.0 ns min at 5 V) and setup/hold requirements (ts = 7.0 ns, th = 2.5 ns). Based on these, reliable operation is achievable up to approximately 80 MHz for clean, well-terminated clock signals. The MC74ACT646NG is intended for synchronous bus control-not free-running clocking-and its performance depends on proper PCB layout and load capacitance management.

Does the MC74ACT646NG support hot insertion or live bus swapping?

No, the MC74ACT646NG is not designed for hot insertion. Its absolute maximum ratings do not include powered-insertion stress testing, and the input structure lacks dedicated hot-swap protection circuitry. Applying voltage to A/B bus pins while VCC is unpowered may exceed VI limits (−0.5 V to VCC+0.5 V) and risk latch-up. For live-swapping applications, external protection such as series resistors and TVS diodes is required. The MC74ACT646NG should only be powered and operated within its recommended conditions.

Can the MC74ACT646NG operate at 3.3 V supply?

No, the MC74ACT646NG is not rated for 3.3 V operation. Its recommended VCC range is strictly 4.5–5.5 V, and DC characteristics (e.g., VIH = 2.0 V min) are only guaranteed within that range. At 3.3 V, input thresholds become unreliable, output drive degrades significantly, and AC timing parameters fall outside specification. For 3.3 V systems, consider the 74LVT646 or 74ALVCH16646 families instead. The MC74ACT646NG must be used at 5 V nominal.

How does the DIR pin interact with the SAB and SBA control signals in the MC74ACT646NG?

In the MC74ACT646NG, DIR selects data direction while SAB/SBA select data source: DIR = H enables A→B transfer, and DIR = L enables B→A transfer; SAB = L selects real-time A data, SAB = H selects stored A data; similarly, SBA = L selects real-time B data, SBA = H selects stored B data. All combinations are valid per the function table. The MC74ACT646NG uses this dual-control scheme to decouple flow direction from data origin, enabling flexible protocol implementations like echo-back testing or dual-buffered transfers.

Is the MC74ACT646NG pin-compatible with the MC74AC646NG?

Yes, the MC74ACT646NG is pin-compatible with the MC74AC646NG-both share identical SOIC-24 pinout, register architecture, and control logic-but differ in input threshold compatibility: MC74ACT646NG has TTL-compatible inputs (VIH = 2.0 V), while MC74AC646NG uses CMOS thresholds (VIH = 3.15 V at 4.5 V). Swapping them requires verifying upstream driver logic levels; otherwise, marginal noise margins or functional failure may occur. The MC74ACT646NG is not a drop-in replacement without signal-level validation.