onsemi DM74AS245N

Overview

DM74AS245N from Fairchild Semiconductor is an octal bus transceiver with independent 3-STATE control on A and B buses, designed for bidirectional data transfer in memory and microprocessor systems. It operates at VCC = 4.5–5.5 V, delivers ±48 mA output drive, achieves 2–7.5 ns propagation delay, and supports isolation via G (enable) and DIR (direction) inputs. Used in asynchronous bus interfacing between TTL and CMOS subsystems.

For engineers reviewing the DM74AS245N datasheet, pinout, applications, or equivalent options, key selection factors include its 20-pin PDIP package, dual-bus 3-STATE control logic, guaranteed switching performance across 0°C to 70°C, and compatibility with terminated transmission lines down to 133 Ω.

Technical Context

The DM74AS245N implements eight non-inverting bidirectional buffer pairs with separate enable (G) and direction (DIR) control signals. Its oxide-isolated, ion-implanted Schottky TTL process ensures fast switching and low input loading via PNP inputs.

Each A/B port pair operates independently under DIR logic: DIR = L enables B→A transfer; DIR = H enables A→B transfer; G = H forces all outputs into high-impedance state regardless of DIR. Output drive capability (IOL = 48 mA, IOH = −15 mA) and VOH = VCC − 2 V specification ensure reliable interfacing with CMOS loads.

Key Specifications

Pinout & Package

DM74AS245N is housed in a 20-lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001 compliant, 0.300 inch wide, with through-hole mounting and standard DIP footprint.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74AS245N and 74F245PC, the DM74AS245N offers balanced 48 mA drive and 7.5 ns timing-ideal for general-purpose bus isolation where robust load driving and commercial temperature range are prioritized over marginal speed gains.

Availability

DM74AS245N is available at Aetrix Electronics and suitable for memory subsystems, microprocessor bus interfaces, and legacy industrial backplane designs requiring stable component supply and long-term obsolescence management.

Supply support for DM74AS245N 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 designer of high-performance analog and logic ICs, acquired by ON Semiconductor in 2016; legacy products remain widely supported.

The DM74AS245N belongs to Fairchild's advanced Schottky TTL logic family, engineered for high-speed, low-noise bidirectional data transfer in computing and industrial control systems.

FAQ

What is the maximum operating temperature range for the DM74AS245N?

The DM74AS245N is rated for operation from 0°C to +70°C ambient temperature. This commercial-grade range is specified across all electrical parameters including propagation delay, output drive, and input thresholds. The device's thermal resistance (θJA = 51.5°C/W in PDIP) supports reliable operation within this range when mounted on standard FR-4 PCBs with adequate copper area. Exceeding 70°C may cause parameter drift or premature failure.

Does the DM74AS245N support true bidirectional data flow without external logic?

Yes, the DM74AS245N supports true bidirectional data flow using only its two control inputs: DIR selects direction (A→B or B→A), and G enables/disables all outputs. No external gates or latches are needed. When G = L, data flows according to DIR; when G = H, both A and B ports enter high-impedance state, electrically isolating the buses. This native dual-control architecture simplifies board layout and reduces component count in bus interface designs.

Can the DM74AS245N drive a 50 Ω transmission line?

No, the DM74AS245N is not rated to directly drive a 50 Ω transmission line. Its output stage is characterized for 133 Ω termination and switching into 500 Ω/50 pF loads. Driving 50 Ω would exceed its IOL rating (48 mA max) and risk excessive power dissipation or waveform distortion. For 50 Ω systems, use a dedicated line driver or add series termination; the DM74AS245N is intended for board-level, medium-length parallel buses-not RF or high-speed serial links.

Is the DM74AS245N pin-compatible with the 74LS245?

No, the DM74AS245N is not pin-compatible with the 74LS245. While both are 20-pin octal transceivers with identical pin numbering (G, A1–A8, GND, B1–B8, DIR, VCC), their electrical behavior differs significantly: DM74AS245N has higher drive (48 mA vs. 24 mA), faster timing (2–7.5 ns vs. 6–22 ns), and different input thresholds. Substitution requires validation of timing margins, loading, and power delivery-no drop-in replacement is assured.

What is the purpose of the PNP input structure in the DM74AS245N?

The PNP input structure in the DM74AS245N reduces input loading current: IIH ≤ 20 µA (control inputs) and ≤ 70 µA (A/B ports), and IIL ≤ −0.5 mA (control) or −0.75 mA (ports). This minimizes capacitive and DC loading on upstream drivers-critical in fan-out-limited TTL systems. It also improves noise immunity and allows more devices per driving gate compared to standard TTL inputs, extending bus length and reliability in dense logic designs.