Texas Instruments SN74ALS273NSR

Overview

SN74ALS273NSR from Texas Instruments is an octal positive-edge-triggered D-type flip-flop with asynchronous clear, implemented in ALS TTL logic. It features eight independent D-inputs, a common buffered clock (CLK), and a shared direct-clear (CLR) input. Rated for 0°C to 70°C operation, it delivers 35 MHz maximum clock frequency, 12 mA low-level output drive, and 24 mA sink capability - used in synchronous data latching and register staging within industrial control logic and legacy digital systems.

For engineers reviewing the SN74ALS273NSR datasheet, SN74ALS273NSR pinout, SN74ALS273NSR application, or SN74ALS273NSR equivalent, key selection criteria include its 20-pin SOP (NS) package, TTL-compatible voltage thresholds (VIH = 2 V, VIL = 0.8 V), guaranteed setup/hold timing (tsu = 10 ns, th = 0 ns), and compatibility with 5-V-only bus interfaces requiring deterministic edge-triggered storage.

Technical Context

This device implements eight independent D-type latches synchronized to the rising edge of CLK, with asynchronous active-low CLR overriding clock action. Each flip-flop transfers D-input state to Q-output only on CLK's positive transition, provided setup time (10 ns) is met; no metastability tolerance or internal Schmitt triggering is specified.

It uses bipolar ALS (Advanced Low-Power Schottky) TTL technology, delivering higher speed and lower power than standard LS TTL while maintaining pin- and logic-compatible behavior with SN74LS273. Output structure is totem-pole (non-open-collector), supporting direct interfacing with other TTL loads without pull-ups.

Key Specifications

Pinout & Package

SOP-20 (NS) package: 0.300-inch body width, 1.27 mm pitch, 2.65 mm max height, RoHS-compliant NiPdAu lead finish, moisture sensitivity level 1 (260°C peak reflow).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal D-type flip-flop applications.

Compared with SN74LS273N and SN74HC273PW, SN74ALS273NSR provides the highest speed among TTL-compatible octal D flip-flops in SOP packaging, enabling tighter timing in bus-hold and register-file applications without redesigning signal integrity or voltage translation.

Availability

SN74ALS273NSR is available at Aetrix Electronics and suitable for industrial control panels, legacy instrumentation interfaces, and retro-computing hardware requiring stable component supply and long-term obsolescence management.

Supply support for SN74ALS273NSR 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic ICs for industrial, automotive, and communications markets.

The SN74ALS273NSR belongs to TI's legacy 74ALS logic family, designed specifically for high-speed, low-power 5-V TTL system interfacing - targeting register, latch, and clock-synchronized data path functions in mid-1980s–1990s digital equipment.

FAQ

What is the maximum clock frequency supported by SN74ALS273NSR?

The SN74ALS273NSR supports a maximum clock frequency of 35 MHz under recommended operating conditions (VCC = 4.5 V to 5.5 V, CL = 50 pF, TA = 0°C to 70°C). This rating is verified by TI's switching characteristics table and applies to the SOP-20 (NS) package variant. Exceeding this frequency may result in setup/hold violations or metastability, especially with marginal PCB layout or load capacitance.

Does SN74ALS273NSR have 3-state outputs?

No, SN74ALS273NSR does not feature 3-state outputs. Its Q outputs use a totem-pole (push-pull) structure with defined high and low logic states only. It lacks output-enable (OE) control, so outputs remain active at all times - unlike variants such as SN74ALS373. This makes SN74ALS273NSR suitable for point-to-point latching but not for shared bus applications without external isolation.

Can SN74ALS273NSR operate at 3.3 V?

No, SN74ALS273NSR cannot reliably operate at 3.3 V. Its absolute maximum VCC is 7 V, but the recommended operating range is strictly 4.5 V to 5.5 V. At 3.3 V, ALS TTL circuitry fails to meet VIH (2 V min) and VOL (0.4 V max) specifications, resulting in undefined logic states and excessive propagation delay. Use SN74LVC273 or similar 3.3-V CMOS alternatives instead.

What is the purpose of the CLR pin on SN74ALS273NSR?

The CLR (pin 1) on SN74ALS273NSR is an asynchronous active-low clear input that forces all eight Q outputs to logic low immediately, independent of the clock signal. When asserted (low), it overrides any D-input or CLK activity. Release of CLR allows subsequent CLK edges to resume normal D-to-Q transfer. This function enables system-wide reset or initialization without requiring precise clock alignment.

Is SN74ALS273NSR pin-compatible with SN74LS273N?

Yes, SN74ALS273NSR is functionally and pin-compatible with SN74LS273N in terms of logic behavior, pin assignment, and electrical interface - both use identical 20-pin DIP/SOP pinouts and share the same terminal functions (CLR, D1–D8, Q1–Q8, CLK, VCC, GND). However, SN74ALS273NSR uses SOP-20 (NS) packaging versus PDIP-20 (N), requiring PCB land pattern adaptation despite identical pin numbering and signal mapping.