Texas Instruments SN74HC148NSR

Overview

SN74HC148NSR 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 (4-2-1) output with cascading enable (EI/EO) and group-select (GS) signals. It delivers 4-mA output drive at 5V, 16ns typical propagation delay, and supports industrial temperature range (–40°C to +85°C) in SOP-16 package.

For engineers reviewing the SN74HC148NSR datasheet, SN74HC148NSR pinout, SN74HC148NSR application, or SN74HC148NSR equivalent, key selection criteria include low-power operation (80-μA max ICC), active-low logic compatibility, cascading capability for multi-stage encoding, and verified performance across 2V–6V VCC with LSTTL load drive.

Technical Context

The SN74HC148NSR implements combinational priority encoding where only the highest-order asserted (low) input determines the output code; all inputs and outputs are active-low. Its functional modes include enabled encoding (EI = L), disabled output (EI = H), and cascaded operation via EO/GS handshake signals that allow expansion beyond eight lines without external logic.

It features standard CMOS input thresholds (VIH = 3.15V @ VCC = 4.5V, VIL = 1.35V), guaranteed switching characteristics (tpd ≤ 45ns @ VCC = 4.5V, CL = 50pF), and robust DC specs including ±4-mA output drive, 1μA max input current, and 35pF power dissipation capacitance.

Key Specifications

Pinout & Package

SOP-16 package (NS), body size 10.20 mm × 5.30 mm, 1.27-mm pitch, 2.00-mm max height, RoHS-compliant NIPDAU lead finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC148NSR, SN74LS148N trades speed and power efficiency for TTL compatibility, while CD40147BE offers broader VCC tolerance but sacrifices integrated cascading - making SN74HC148NSR optimal for modern low-voltage, multi-stage encoding where pinout consistency and minimal external components are critical.

Availability

SN74HC148NSR is available at Aetrix Electronics and suitable for industrial I/O expansion, keyboard matrix encoding, multi-stage interrupt controllers, and legacy bus address decoding requiring stable component supply and long-term manufacturability.

Supply support for SN74HC148NSR 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 logic solutions with emphasis on reliability, scalability, and broad design support.

The SN74HC148NSR belongs to TI's 74HC logic family, engineered for high-speed, low-power CMOS operation in industrial control, instrumentation, and digital system interfacing applications.

FAQ

What is the function of the GS (Group Select) pin on the SN74HC148NSR?

The GS pin on the SN74HC148NSR is an active-low output that indicates whether any input (I0–I7) is asserted: GS = L when at least one input is low, and GS = H when all inputs are high. This signal validates the integrity of the encoded output (A2–A0) and is essential for detecting idle states in priority-encoded systems. In the SN74HC148NSR, GS works in conjunction with EO to manage cascaded configurations reliably.

Can the SN74HC148NSR operate at 3.3V supply voltage?

Yes, the SN74HC148NSR is fully specified for operation at 3.3V: VIH = 2.31V (min), VIL = 0.99V (max), and output drive remains compliant at ±4 mA. Its 2V–6V VCC range makes it interoperable with 3.3V microcontrollers and FPGAs without level shifters. All timing and electrical parameters in the SN74HC148NSR datasheet are validated across this full range, including at 3.3V.

How does cascading work between two SN74HC148NSR devices?

Cascading two SN74HC148NSR devices uses EI, EO, and GS signals: the EO of the lower-priority encoder connects to the EI of the higher-priority one. When the first encoder detects no active input, its EO goes low, enabling the second encoder. GS from both devices combines via wired-OR (or external OR gate) to indicate overall activity. This hierarchical structure preserves priority order across 16 inputs using only native SN74HC148NSR pins - no additional logic required.

Is the SN74HC148NSR pin-compatible with the SN74HC148N (PDIP-16)?

Yes, the SN74HC148NSR (SOP-16) shares identical pin numbering, pin functions, and logic behavior with the SN74HC148N (PDIP-16). Both follow the same J, D, N, NS package pinout per TI's SCLS109H datasheet. However, due to differing package dimensions and thermal characteristics, PCB layout and reflow profiles must be adjusted - the SN74HC148NSR requires SOP-specific footprint and stencil design per NS0016A outline.

What is the maximum capacitive load the SN74HC148NSR can drive while maintaining specified tpd?

The SN74HC148NSR switching characteristics are characterized at CL = 50 pF, and tpd degrades predictably beyond that: at CL = 100 pF, typical tpd increases to ~65 ns (VCC = 4.5V). For reliable operation within datasheet limits, keep total load (including trace capacitance and input capacitance of downstream devices) ≤50 pF. If heavier loads are unavoidable, derate timing margins accordingly - the SN74HC148NSR itself does not specify absolute maximum CL, but sustained operation above 100 pF may impact noise immunity and rise/fall times.