Texas Instruments SN74HC148DG4

Overview

SN74HC148DG4 from Texas Instruments is an 8-line to 3-line priority encoder IC operating at 2V–6V supply, encoding eight active-low inputs into a 3-bit binary output (A0–A2), with cascading support via EI/EO control lines and active-low group select (GS) and enable output (EO) signals. It delivers 4-mA output drive at 5V, 16ns typical propagation delay, and ≤80-μA supply current - used in industrial control panels for fault-priority signal encoding.

For engineers reviewing the SN74HC148DG4 datasheet, SN74HC148DG4 pinout, SN74HC148DG4 application, or SN74HC148DG4 equivalent, key selection criteria include low-power CMOS compatibility, cascading capability for multi-stage encoding, active-low logic interface requirements, and SOIC-16 thermal performance under -40°C to +85°C industrial conditions.

Technical Context

The SN74HC148DG4 implements combinational priority encoding with strict highest-order-input precedence: only the lowest-numbered asserted (low) input among I0–I7 determines the output code. Its functional modes are fully defined by EI (enable input), with EO (enable output) and GS (group select) providing hierarchical cascade signaling without external logic.

Input and output signals operate at standard HC CMOS voltage thresholds (VIH = 3.15V min at VCC = 4.5V; VOL = 0.33V max at IOL = 4mA), and all unused inputs must be tied to VCC or GND to prevent floating states - critical for deterministic operation in noise-prone industrial environments.

Key Specifications

Pinout & Package

SN74HC148DG4 is housed in a 16-pin SOIC (D) package measuring 9.90 mm × 3.90 mm with 1.27-mm pitch, optimized for surface-mount assembly and thermal dissipation (RθJA = 73°C/W).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS148N, SN74HC148DG4 offers wider voltage range and lower power; compared with 74HC148PW, it provides superior thermal performance and broader manufacturing compatibility - making SN74HC148DG4 optimal for industrial-grade reliability and design flexibility.

Availability

SN74HC148DG4 is available at Aetrix Electronics and suitable for industrial control panels, automated test equipment, motor drive interfaces, and power supply monitoring systems requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for SN74HC148DG4 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 for industrial, automotive, and consumer applications.

The SN74HC148DG4 belongs to TI's 74HC logic family, engineered for high-speed, low-power CMOS operation in industrial control, instrumentation, and digital system interfacing - emphasizing robustness, wide supply tolerance, and seamless integration with microcontrollers and FPGAs.

FAQ

What is the logic polarity of inputs and outputs on the SN74HC148DG4?

The SN74HC148DG4 uses active-low logic throughout: all eight data inputs (I0–I7), EI, EO, GS, and the three binary outputs (A0–A2) are asserted low. This means a logic '0' on I7 takes precedence over any other low input, and A0–A2 output the complement of the true binary index (e.g., I3 asserted yields A2=0, A1=0, A0=0). This polarity is fixed and cannot be inverted internally.

Can multiple SN74HC148DG4 devices be cascaded, and how is it implemented?

Yes, SN74HC148DG4 supports hardware cascading using EI, EO, and GS signals. Connect EO of a lower-priority stage to EI of the next higher-priority stage. When no inputs are active in the first stage, EO goes low, enabling the second stage. GS indicates valid encoding output. This allows building 16-, 24-, or N-input encoders without external logic, preserving timing integrity and minimizing board area.

What is the maximum capacitive load the SN74HC148DG4 can drive reliably?

The SN74HC148DG4 is characterized for CL = 50 pF in switching specifications, with tpd and tt values guaranteed under that condition. While it can drive heavier loads, propagation delay increases linearly with capacitance - e.g., 100 pF may add ~5–8 ns to tpd. For reliable operation beyond 50 pF, add a buffer stage or verify timing margins in the target application using the SN74HC148DG4's published Cpd = 35 pF and output drive specs.

Does the SN74HC148DG4 require external pull-up resistors on its inputs?

No - external pull-ups are not required but strongly recommended for unused inputs. All unused data inputs (I0–I7), EI, and outputs must be terminated to VCC or GND to prevent floating states that cause excessive ICC or erratic encoding. TI specifies tying unused inputs to VCC or GND per SCBA004; pull-up resistors (e.g., 10 kΩ to VCC) are common for Ix inputs to default to inactive (high) state in open-collector-like configurations.

How does the SN74HC148DG4 handle simultaneous assertion of multiple inputs?

The SN74HC148DG4 resolves simultaneous low assertions strictly by priority: I7 has highest priority, then I6, down to I0 as lowest. Only the highest-priority asserted input determines the output code (A0–A2) and sets GS low. Lower-priority inputs are ignored during that cycle - no arbitration delay or metastability occurs, as encoding is purely combinational and deterministic per the function table.