NXP Semiconductors N74F85D,512

Overview

N74F85D,512 from Philips Semiconductors is a 4-bit magnitude comparator IC used to determine relative binary word size in digital logic systems. It features active-High A>B, A=B, and AB/A

For engineers reviewing the N74F85D,512 datasheet, N74F85D,512 pinout, N74F85D,512 application, or N74F85D,512 equivalent, key selection criteria include its 16-pin SO package (SOT162-1), TTL-compatible input thresholds (VIH = 2.0 V, VIL = 0.8 V), fan-out capability (50/33 U.L. High/Low), and defined expansion interface (IA>B, IA=B, IA

Technical Context

The N74F85D,512 implements combinational logic to compare two 4-bit monotonic codes (binary, BCD) using weighted inputs A0–A3 and B0–B3, with A3/B3 as MSBs. Its three mutually exclusive outputs reflect magnitude relationships only when expansion inputs are properly biased for standalone use (IA>B = Low, IA=B = High, IA

In parallel expansion mode, IA>B, IA=B, and IA

Key Specifications

Pinout & Package

Package: 16-lead plastic small outline (SO), body width 7.5 mm, JEDEC MO-153 compliant (SOT162-1).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 4-bit magnitude comparator applications.

Compared with SN74F85N and 74ACT85SCX, the N74F85D,512 offers identical logic functionality in a space-saving SO package with proven 74F timing and drive strength, making it optimal for high-density commercial-grade digital boards requiring drop-in 74F compatibility.

Availability

N74F85D,512 is available at Aetrix Electronics and suitable for microprocessor address decoding, digital comparator subsystems, BCD-based instrument displays, and industrial control logic sequencing requiring stable component supply and long-term obsolescence management.

Supply support for N74F85D,512 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

Philips Semiconductors (now NXP Semiconductors) was a leading European semiconductor supplier known for robust logic families and industrial-grade analog products.

The 74F logic series-including N74F85D,512-was engineered for high-speed commercial applications demanding reliable TTL-compatible performance with reduced power-delay product versus standard 74LS.

FAQ

What is the correct biasing for IA>B, IA=B, and IA

For standalone operation, tie IA>B and IAB, A=B, and A

Does N74F85D,512 support BCD comparison, and how is that validated in the datasheet?

Yes, N74F85D,512 explicitly supports BCD and other monotonic codes, as stated in the "DESCRIPTION" section: "It compares two 4-bit binary, BCD, or other monotonic codes." The function table and logic diagram confirm bit-wise weighted comparison without assumptions about encoding, and application examples include BCD-based instrument displays. No recoding or additional logic is required for BCD use.

What is the maximum number of N74F85D,512 devices that can be cascaded in parallel expansion, and what is the resulting propagation delay?

Per the datasheet's Table 1, up to 31 N74F85D,512 devices can be cascaded for 25–120-bit comparisons, with worst-case propagation delay of 34 ns. This value accounts for cumulative delays across all stages and is measured under standard test conditions (CL = 50 pF, RL = 500 Ω, VCC = 5.0 V). The delay scales predictably due to fixed per-stage contribution.

How does the input loading of N74F85D,512 compare to standard 74F-series inputs, and why does it matter?

N74F85D,512 features high-impedance NPN base inputs drawing only ±20 µA in High/Low states-significantly less than typical 74F inputs (~1.6 mA Low, 0.04 mA High). This reduces loading on upstream drivers, enabling >50 fan-out without signal degradation. The datasheet highlights this as a key feature for dense logic designs where drive capability is constrained.

Is N74F85D,512 pin-compatible with SN74F85N, and what design changes are needed for substitution?

Yes, N74F85D,512 and SN74F85N share identical pin functions and electrical specifications; only the package differs (SO vs. DIP). No PCB layout or schematic changes are required-only reflow vs. through-hole assembly process adaptation. The datasheet confirms identical pin configuration diagrams and function tables, validating direct functional equivalence across packages.