Texas Instruments SN74ALS29845NT

Overview

SN74ALS29845NT from Texas Instruments is an 8-bit noninverting D-type latch with three-state outputs, designed for bus interface applications in TTL-compatible systems. It features buffered OC1/OC2/OC3 control inputs, power-up high-impedance outputs, and supports ±24 mA high-level / +48 mA low-level output drive at 5 V. Used in address/data bus expansion and I/O port buffering.

For engineers reviewing the SN74ALS29845NT datasheet, SN74ALS29845NT pinout, SN74ALS29845NT application, or SN74ALS29845NT equivalent, key selection criteria include bus-structured pinout compatibility, 3-state output timing (tPLH/tPHL ≤ 8 ns @ 5 V), latch transparency behavior, and operation across 0°C to 70°C industrial temperature range.

Technical Context

This device implements eight independent transparent D-type latches with asynchronous preset (PRE) and clear (CLR), where PRE and CLR operate independently of clock (C) and override data input. Output enable is controlled by three buffered OC inputs (OC1, OC2, OC3), allowing flexible 3-state activation without affecting internal latch state.

Logic operation follows a defined function table: outputs enter high-impedance (Z) when any OC input is high; Q retains prior state when OCs are low and C is stable; data propagates on C high-to-low transition. Power-up and power-down default to high-Z, preventing bus contention during supply ramp.

Key Specifications

Pinout & Package

SN74ALS29845NT is supplied in a 24-pin plastic DIP (Dual In-line Package) with 300-mil width, pin-compatible with industry-standard through-hole PCB layouts.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 8-bit bus latch applications.

Compared with SN74ALS29845NT, SN74ALS244N provides no storage capability and cannot replace it in address/data capture roles, while SN74LS373N offers functional equivalence with reduced drive strength, slower timing, and simplified output control - making SN74ALS29845NT preferable for high-fanout, multi-control bus systems.

Availability

SN74ALS29845NT is available at Aetrix Electronics and suitable for memory address latching, I/O port expansion, parity bus buffering, and legacy system bus isolation requiring stable component supply and long-term industrial availability.

Supply support for SN74ALS29845NT 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, delivering analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74ALS29845NT belongs to TI's legacy Advanced LS (ALS) logic family, engineered for high-speed, low-power 5 V TTL bus interfacing in mid-1980s computing and instrumentation systems.

FAQ

What is the logic family and voltage rating of the SN74ALS29845NT?

The SN74ALS29845NT belongs to the Advanced Low-Power Schottky (ALS) TTL logic family and operates strictly within 4.75 V to 5.25 V supply range. Its input thresholds (VIH ≥ 2 V, VIL ≤ 0.8 V) and output drive levels are fully compatible with standard 5 V TTL systems, ensuring interoperability with legacy microprocessors, peripherals, and bus controllers without level translation.

Does the SN74ALS29845NT support true three-state control with multiple enable inputs?

Yes, the SN74ALS29845NT implements three independent buffered output control inputs - OC1, OC2, and OC3 - wired in OR logic. Any one of these inputs driven high places all eight outputs (1Q–8Q) into high-impedance state, enabling flexible bus arbitration schemes. This differs from single-OE latches and supports complex bus sharing protocols in multi-master systems.

How does the SN74ALS29845NT behave during power-up and power-down?

The SN74ALS29845NT guarantees high-impedance outputs during both power-up and power-down transitions. This prevents bus contention and signal corruption when VCC is ramping, a critical feature for hot-swap-capable or gracefully powered systems. The outputs remain in Z-state until VCC stabilizes and control inputs settle - no external reset sequencing is required.

Can the SN74ALS29845NT be used as a replacement for the SN74LS373N?

The SN74ALS29845NT shares functional similarity with the SN74LS373N as an 8-bit D latch but is not pin-compatible due to different pin assignments (e.g., OC1/OC2/OC3 vs single OE) and added PRE/CLR functionality. While both perform latching, SN74ALS29845NT offers higher drive, faster timing, and multi-control flexibility - substitution requires PCB layout revision and firmware adaptation for OC logic.

What are the absolute maximum ratings for the SN74ALS29845NT?

The SN74ALS29845NT has an absolute maximum supply voltage of 7 V, input voltage limit of 7 V, and disabled 3-state output voltage tolerance of 5.5 V. Storage temperature ranges from –65°C to +150°C. Exceeding these limits may cause permanent damage. Functional operation is only guaranteed within recommended conditions: VCC = 4.75–5.25 V and TA = 0°C to 70°C.