Texas Instruments SN74HC148DRG4

Overview

SN74HC148DRG4 from Texas Instruments is an 8-line to 3-line priority encoder IC operating at 2V–6V supply, encoding active-low inputs into 3-bit binary (A0–A2) with enable control (EI/EO), propagation delay as low as 38ns at 6V, and ±4-mA output drive at 5V - used in keyboard scan logic and interrupt prioritization circuits.

For engineers reviewing the SN74HC148DRG4 datasheet, SN74HC148DRG4 pinout, SN74HC148DRG4 application, or SN74HC148DRG4 equivalent, key selection considerations include active-low input/output polarity, cascading capability via EI/EO, SOIC-16 package compatibility, and TTL-load driving capability up to 10 LSTTL units.

Technical Context

The SN74HC148DRG4 implements combinational priority encoding where only the highest-order asserted (low) input determines the 3-bit binary output; all inputs and outputs are active-low, requiring external pull-ups for open-collector-like behavior. Its EI and EO signals support daisy-chained expansion without external gates.

It operates in standard CMOS logic family with rail-to-rail input voltage tolerance (0–VCC), input clamp current ±20 mA, and junction temperature rating up to 150°C - designed for deterministic encoding under transient conditions while avoiding metastability through priority resolution.

Key Specifications

Pinout & Package

SN74HC148DRG4 uses a 16-pin SOIC (D) package measuring 9.90 mm × 3.90 mm with 1.27-mm pitch, compliant with JEDEC MS-012, and rated MSL Level-1 (unlimited floor life at ≤30°C/60% RH).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar priority encoder applications.

Compared with SN74LS148N, SN74HC148DRG4 delivers 2.6× faster propagation, 250× lower quiescent current, and native multi-stage cascading; versus 74HC148PW, it offers identical functionality in a wider SOIC body preferred for manual assembly and thermal dissipation.

Availability

SN74HC148DRG4 is available at Aetrix Electronics and suitable for industrial I/O modules, keyboard scan interfaces, and interrupt arbitration circuits requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant packaging.

Supply support for SN74HC148DRG4 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

Texas Instruments is a global semiconductor leader delivering analog, embedded processing, and connectivity solutions with over 90 years of innovation in industrial, automotive, and consumer electronics.

The SN74HC148DRG4 belongs to TI's 74HC logic family - engineered for high noise immunity, low power, and seamless integration into mixed-signal control systems where deterministic priority resolution is critical.

FAQ

What is the function of the GS pin on the SN74HC148DRG4?

The GS (Group Select) pin on the SN74HC148DRG4 is an active-low output that goes low whenever any of the eight data inputs (I0–I7) is asserted (low), indicating that a valid encoded output is present on A0–A2. It serves as a ready flag for downstream logic or microcontrollers to sample the encoded value only when meaningful data exists - preventing reads during idle or indeterminate states.

Can the SN74HC148DRG4 operate at 3.3 V?

Yes, the SN74HC148DRG4 operates reliably at 3.3 V, as confirmed by its recommended operating condition range of 2 V to 6 V. At 3.3 V, it maintains full logic-level compatibility with 3.3-V microcontrollers and FPGA I/O banks, delivers ±4-mA output drive, and achieves typical propagation delay of ~45 ns - making it suitable for mixed-voltage embedded systems without level-shifting circuitry.

How does cascading work with multiple SN74HC148DRG4 devices?

Cascading SN74HC148DRG4 devices uses the EI (Enable Input) and EO (Enable Output) pins: the EO of a higher-priority stage connects to the EI of the next-lower stage. When no input is active in the first encoder, EO goes low, enabling the second - allowing up to 64 inputs (eight 8-line encoders) to be prioritized hierarchically. No external logic is required, preserving timing integrity and minimizing board area.

Why must unused inputs on the SN74HC148DRG4 be tied to VCC?

Unused inputs on the SN74HC148DRG4 must be tied to VCC (not left floating) because CMOS inputs exhibit undefined logic states and increased susceptibility to noise when unconnected - potentially causing false triggering, excessive current draw, or oscillation. TI specifies this in Section 6.2: tying to VCC ensures predictable high-level input behavior and prevents unintended activation of lower-priority inputs during system startup or fault conditions.

Is the SN74HC148DRG4 pin-compatible with older 74LS148 variants?

No, the SN74HC148DRG4 is not pin-compatible with 74LS148 variants despite identical pin numbering - differences in internal architecture (e.g., LS148 lacks dedicated EO/GS functions and uses different enable logic) and electrical characteristics (TTL vs. CMOS thresholds, drive strength, and timing) prevent drop-in replacement. Board redesign and signal validation are required when migrating from LS to HC families.