onsemi MC74AC20MELG

Overview

MC74AC20MELG from onsemi is a dual 4-input NAND gate in high-performance silicon-gate CMOS technology, operating at supply voltages from 2.0 V to 6.0 V, delivering ±24 mA output drive, with propagation delays as low as 1.5 ns (tPHL/tPLH) at 5.0 V and 50 pF load, used in digital logic control, address decoding, and bus interface circuits.

For engineers reviewing the MC74AC20MELG datasheet, pinout, applications, or equivalent options, this page provides verified functional identity, SOIC-14 pin mapping, DC/AC electrical specifications across temperature, TTL-compatible input distinction (vs. MC74ACT20), and real-world substitution guidance for logic-level translation and combinational logic design.

Technical Context

The MC74AC20MELG implements two independent 4-input NAND gates in a single SOIC-14 package, with CMOS inputs exhibiting high noise immunity and rail-to-rail voltage thresholds defined per VCC (e.g., VIH = 2.1 V min at VCC = 3.0 V). It lacks Schmitt-trigger inputs and requires monotonic input transitions within specified rise/fall time limits (e.g., ≤25 ns/V at VCC = 5.5 V).

Its output stage supports symmetrical sourcing and sinking of up to 24 mA per gate, enabling direct LED driving or fan-out to multiple 74AC/74ACT loads. Quiescent ICC remains ≤40 µA over −40°C to +85°C, and dynamic output current capability reaches ±75 mA under pulsed conditions (VOLD ≤1.65 V / VOHD ≥3.85 V).

Key Specifications

Pinout & Package

MC74AC20MELG is housed in a Pb-free SOIC-14 (Case 751A) package, 8.55 mm × 3.80 mm footprint, 1.27 mm pitch, with 1.75 mm max height and moisture sensitivity level (MSL) 1 - suitable for standard reflow assembly without dry-pack requirements.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual 4-input NAND gate applications.

Compared with MC74ACT20DR2G and SN74AC20N, MC74AC20MELG offers optimal balance of wide supply range (2.0–6.0 V), Pb-free SOIC-14 manufacturability, and industrial temperature support - making it the default choice for new SMT-based embedded logic designs requiring flexibility and compliance.

Availability

MC74AC20MELG is available at Aetrix Electronics and suitable for industrial automation, automotive body electronics, and medical device logic subsystems requiring stable component supply, RoHS compliance, and long-term lifecycle assurance.

Supply support for MC74AC20MELG 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 specializing in energy-efficient power, analog, sensors, and logic solutions for automotive, industrial, and cloud infrastructure markets.

The MC74AC20MELG belongs to the 74AC logic family - designed for high-speed, low-power CMOS applications where rail-to-rail compatibility, wide VCC range, and robust output drive are essential in space-constrained embedded systems.

FAQ

What logic function does the MC74AC20MELG implement?

The MC74AC20MELG implements two independent 4-input NAND gates. Each gate outputs LOW only when all four inputs (A, B, C, D) are HIGH; otherwise, it outputs HIGH. This Boolean function - Y = NOT(A AND B AND C AND D) - is used for enable logic, signal masking, and combinational decision trees in digital systems. The MC74AC20MELG contains no internal interconnect between the two gates, ensuring fully isolated operation.

Is MC74AC20MELG pin-compatible with MC74ACT20 variants?

Yes, MC74AC20MELG is pin-compatible with MC74ACT20DG and MC74ACT20DR2G - sharing identical SOIC-14 pinout, terminal assignments (including NC pins at 3 and 13), and VCC/GND locations. The only functional difference lies in input threshold voltages: MC74ACT20 has TTL-compatible inputs (VIH = 2.0 V, VIL = 0.8 V at 5 V), while MC74AC20MELG uses CMOS thresholds (VIH = 2.1 V, VIL = 0.9 V at 3 V). No PCB changes are required for substitution.

What is the maximum operating frequency for MC74AC20MELG in a 50 pF load configuration?

The MC74AC20MELG does not specify a maximum clock frequency, as it is a combinational logic device without internal clocking. Its usable toggle rate is determined by propagation delay: at VCC = 5.0 V and CL = 50 pF, tPHL/tPLH is 1.0 ns (min) to 8.0 ns (max), supporting logic path frequencies up to ~125 MHz in worst-case cascaded configurations. Real-world performance depends on fan-out, trace capacitance, and supply stability - the MC74AC20MELG itself imposes no inherent frequency ceiling beyond these timing limits.

Can MC74AC20MELG drive LEDs directly?

Yes, MC74AC20MELG can drive LEDs directly due to its ±24 mA output capability per gate. When configured as an active-low driver (LED anode to VCC, cathode to O0/O1), the MC74AC20MELG sinks up to 24 mA - sufficient for standard 2–20 mA indicator LEDs. A current-limiting resistor must be used (e.g., 200 Ω for 5 V supply and 20 mA). Avoid sustained DC operation above 24 mA to prevent exceeding absolute maximum ratings; the MC74AC20MELG is not rated for continuous >24 mA per output.

Does MC74AC20MELG require external pull-up or pull-down resistors on unused inputs?

Yes, all unused inputs of the MC74AC20MELG must be terminated to a valid logic level - either VCC or GND - using pull-up or pull-down resistors (typically 10 kΩ). Floating CMOS inputs cause increased ICC, unpredictable output states, and potential device instability. Since each gate has four inputs, any unconnected A/B/C/D line on either gate must be tied off. The NC pins (3 and 13) are not inputs and must remain unconnected - they serve no internal function and should never be biased.