onsemi DM74AS244N

Overview

DM74AS244N from Fairchild Semiconductor is an advanced Schottky TTL octal 3-STATE non-inverting bus driver in a 20-pin PDIP package, delivering 64 mA sink and −15 mA source output drive, 2–6.2 ns propagation delay, and operation across 0°C to +70°C with VCC = 4.5–5.5 V. It interfaces unidirectional data buses in microprocessor address/data latching and memory read/write control circuits.

For engineers reviewing the DM74AS244N datasheet, pinout, applications, or equivalent options, key selection criteria include 3-STATE enable timing (tPZL ≤ 7.5 ns), CMOS-compatible VOH (≥ VCC − 2 V), high-impedance off-state leakage (IOZL ≤ −50 µA), and compatibility with terminated transmission lines down to 133 Ω.

Technical Context

The DM74AS244N implements eight independent non-inverting buffers, each with individual input (A1–A8) and output (Y1–Y8), grouped into two 4-bit sections sharing active-low 3-STATE enable inputs (G1̅, G2̅). Its oxide-isolated, ion-implanted Schottky TTL process enables faster switching than standard Schottky TTL while reducing power dissipation.

Each buffer drives 500 Ω loads with 50 pF capacitive load, meets TTL input thresholds (VIL ≤ 0.8 V, VIH ≥ 2.0 V), and maintains valid HIGH/LOW output levels under full rated current (VOL ≤ 0.55 V at IOL = 64 mA, VOH ≥ 2.4 V at IOH = −3 mA).

Key Specifications

Pinout & Package

DM74AS244N uses a 20-lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300" wide, with 2.54 mm lead pitch and through-hole mounting. Thermal resistance θJA = 57.0°C/W supports continuous operation at up to 70°C ambient with moderate power dissipation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 3-STATE bus driver applications.

Compared with SN74AS244N and 74F244N, DM74AS244N offers identical performance to the TI variant and superior speed/power trade-off versus the F-series, making it optimal for timing-critical microprocessor bus expansion where legacy compatibility is mandatory.

Availability

DM74AS244N is available at Aetrix Electronics and suitable for microprocessor address buffering, memory read/write latching, and industrial PLC I/O expansion requiring stable component supply over extended production lifecycles.

Supply support for DM74AS244N 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

Fairchild Semiconductor was a U.S.-based semiconductor company specializing in analog and mixed-signal ICs, acquired by ON Semiconductor in 2016. Known for high-performance TTL, MOS, and power management solutions.

The DM74AS244N belongs to Fairchild's Advanced Schottky TTL logic family, engineered for high-speed, low-power bus interface in memory, microprocessor, and communication systems requiring strict TTL compatibility.

FAQ

What is the maximum operating temperature range for DM74AS244N?

The DM74AS244N is specified for operation from 0°C to +70°C ambient temperature. This commercial-grade range aligns with standard TTL system environments such as desktop computers, industrial controllers, and instrumentation. Exceeding +70°C may cause parameter drift or reliability degradation; thermal derating is required above this limit. The DM74AS244N datasheet confirms this range under Recommended Operating Conditions, and its θJA of 57.0°C/W supports safe operation within this envelope under typical PCB layout conditions.

Does DM74AS244N support bidirectional data transfer?

No, DM74AS244N is a unidirectional non-inverting bus driver. Unlike the DM74AS240 (which offers inverting capability), the DM74AS244N provides only non-inverting A→Y signal paths. Bidirectional operation requires external control logic or use of separate transmit/receive drivers. Its dual active-low enables (G1̅, G2̅) allow independent gating of two 4-bit groups but do not change signal directionality. For true bidirectional buffering, designers must select the DM74AS240 or implement discrete directional control.

What is the recommended decoupling for DM74AS244N?

A 0.1 µF ceramic capacitor placed as close as possible to the DM74AS244N VCC (pin 20) and GND (pin 14) pins is recommended. This minimizes high-frequency supply noise induced by fast 3-STATE transitions (tPZL ≤ 7.5 ns) and output switching (tPLH/tPHL ≤ 6.2 ns). For systems with multiple DM74AS244N devices, a bulk 10 µF electrolytic capacitor per 5–10 ICs further stabilizes the local 5 V rail. Layout best practices require short, low-inductance traces between capacitor pads and IC pins to ensure effective noise suppression.

Is DM74AS244N pin-compatible with 74LS244?

Yes, DM74AS244N is functionally and pin-compatible with 74LS244, sharing identical 20-pin PDIP pinout, input/output assignments, and enable logic (active-low G1̅/G2̅). However, DM74AS244N offers faster propagation delays (6.2 ns vs. 15–20 ns), higher output drive (64 mA vs. 24 mA), and lower power consumption. No PCB changes are needed for upgrade, but designers should verify timing margins and ensure adequate decoupling due to increased edge rates.

Can DM74AS244N interface directly with 3.3 V CMOS logic?

DM74AS244N outputs are not 3.3 V tolerant: its VOH minimum is 2.4 V at VCC = 4.5 V, which falls below the 3.3 V CMOS VIH threshold (typically ≥2.7 V). Direct connection risks unreliable HIGH-level recognition. To interface with 3.3 V CMOS, use a level-shifter IC or resistor-based voltage divider on outputs. Inputs are 5 V tolerant and accept 3.3 V logic HIGH (since VIH = 2.0 V max), so 3.3 V CMOS can safely drive DM74AS244N inputs without translation.