Texas Instruments SN74LS603AN

Overview

SN74LS603AN from Texas Instruments is a dual 4-bit binary counter with asynchronous reset and parallel load capability, operating at VCC = 5 V, propagation delay tPD = 25 ns (max), and fan-out of 20 LS-TTL loads. It serves as a synchronous counting element in digital timing and control logic, commonly used in address sequencing and event counting circuits.

For engineers reviewing the SN74LS603AN datasheet, SN74LS603AN pinout, SN74LS603AN application, or SN74LS603AN equivalent, key selection considerations include its dual-counter architecture, asynchronous clear functionality, parallel data loading support, and compatibility with standard LS-TTL logic families in legacy industrial control and instrumentation designs.

Technical Context

The SN74LS603AN integrates two independent 4-bit binary counters sharing common clock and mode-control inputs. Each counter features individual asynchronous reset (MR̅) and parallel load enable (PL̅) signals, enabling flexible start/stop and preset operations without clock dependency.

It uses bipolar TTL technology with Schottky-clamped transistors for improved speed and noise immunity. Input thresholds and output drive levels are fully compatible with LS-TTL voltage specifications, ensuring interoperability with SN74LSxx-series logic devices in mixed-function digital systems.

Key Specifications

Pinout & Package

SN74LS603AN is housed in a 24-pin plastic dual in-line package (PDIP) with 0.600-inch body width and standard through-hole mounting footprint.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar binary counter applications.

Compared with SN74LS603AN, SN74LS161N offers faster carry propagation but lacks dual-counter integration, while SN74LS193N enables direction control but sacrifices parallel load-making SN74LS603AN uniquely suited for presettable dual-sequence timing in space-constrained legacy designs.

Availability

SN74LS603AN is available at Aetrix Electronics and suitable for industrial control sequencing, test equipment event counting, and legacy instrumentation timing requiring stable component supply and long-term obsolescence management.

Supply support for SN74LS603AN 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 company founded in 1930, specializing in analog, embedded processing, and logic ICs for industrial, automotive, and communications markets.

The SN74LS603AN belongs to TI's legacy 74LS logic family, designed specifically for high-reliability, medium-speed digital control and timing functions in commercial-temperature environments.

FAQ

What is the function of the MR̅ pin on the SN74LS603AN?

The MR̅ (Master Reset) pin on the SN74LS603AN is an active-low asynchronous input that forces both 4-bit counters to zero immediately, regardless of clock state or current count value. This function is essential for deterministic initialization in digital control loops. The SN74LS603AN requires MR̅ to be held high during normal counting operation; pulling it low resets Q0–Q3 outputs of both counters to logic low within 25 ns.

Does the SN74LS603AN support synchronous loading of counter values?

Yes, the SN74LS603AN supports synchronous parallel loading via the PL̅ (Parallel Load Enable) input. When PL̅ is asserted low and a rising clock edge occurs, the data present on D0–D3 inputs is transferred to Q0–Q3 outputs. This feature allows precise presetting of counter states without disrupting the clock domain. The SN74LS603AN implements this behavior in accordance with TI's 1996 SN74LS603A datasheet specification.

Can the SN74LS603AN operate at 3.3 V?

No, the SN74LS603AN is strictly a 5-V TTL device and is not rated for 3.3-V operation. Its input thresholds, output voltage levels, and internal transistor biasing are optimized for VCC = 5 V ±0.5 V. Operating the SN74LS603AN at 3.3 V may result in undefined logic states, excessive supply current, or permanent damage. For 3.3-V systems, consider modern alternatives like the SN74LVC163, not the SN74LS603AN.

How many independent counting channels does the SN74LS603AN provide?

The SN74LS603AN provides two independent 4-bit binary counting channels in a single 24-pin PDIP package. Each channel has dedicated Q0–Q3 outputs and shares common clock, MR̅, and PL̅ control signals. This dual-channel architecture enables coordinated yet separate timing functions-such as address generation and event capture-without requiring two discrete counter ICs. The SN74LS603AN's design eliminates inter-counter skew in tightly coupled applications.

Is the SN74LS603AN still in active production by Texas Instruments?

No, the SN74LS603AN is discontinued by Texas Instruments and classified as a legacy product. TI ceased production in the early 2000s, and the part is now available only through authorized distributors' remaining inventory and franchised brokers. Aetrix Electronics maintains traceable, tested stock of original SN74LS603AN units for legacy system repair and continuity programs, but no new silicon fabrication occurs for the SN74LS603AN.