SN74ALS253 - Dual 4:1 Mux 3-State ALS TTL | Texas Instruments
MPN： SN74ALS253 ✗ 停產SN74ALS253 概覽
A multiplexer is a combinational logic device that selects one of several input signals and forwards it to a single output, serving as a fundamental building block in the digital logic hierarchy between basic gates and larger bus-oriented logic systems. The 74-family lineage spans standard TTL (74), Schottky (74S), Low-Power Schottky (74LS), Advanced Low-Power Schottky (74ALS), and CMOS variants such as 74HC and 74HCT.
Key features include full binary decoding with internal inverters and drivers feeding AND-OR gate structures, 3-state outputs that directly drive bus-organized data lines, and the ALS speed-power advantage over LS parts: faster propagation with substantially lower supply current. It is the 3-state version of the ALS153 and SN74AS153, permitting multiplexing from n lines to one line and parallel-to-serial conversion.
Typical applications include bus-organized system data selection, parallel-to-serial data conversion, n-line to 1-line multiplexing in industrial controllers, and legacy TTL system maintenance and repair where ALS-era timing margins must be preserved.
Design consideration: as an older bipolar TTL family, the SN74ALS253 requires a regulated 5V supply and presents TTL-level input thresholds; when integrating into mixed-voltage modern designs, verify logic-level compatibility or consider CMOS substitutes such as 74HC253 with attention to timing.
直接替換替代品，適用於 SN74ALS253 — 相同封裝，腳位對腳位相容。需重新設計 PCB 的不同封裝零件不列入。
SN74AS253A
✅ 直接替換📋 參考替代品（不在目錄中）
SN74LS253
✅ 直接替換 ⚠️ 規格未經驗證📋 參考替代品（不在目錄中）
SN74F253
✅ 直接替換 ⚠️ 規格未經驗證📋 參考替代品（不在目錄中）
SN54ALS253
✅ 直接替換📋 參考替代品（不在目錄中）
SN74HC253
✅ 直接替換 ⚠️ 規格未經驗證📋 參考替代品（不在目錄中）
CD74HC253
✅ 直接替換 ⚠️ 規格未經驗證📋 參考替代品（不在目錄中）
74F253
✅ 直接替換 ⚠️ 規格未經驗證📋 參考替代品（不在目錄中）
SN74ALS253 最大額定值與電氣特性
| 功能 | Dual 1-of-4 Data Selector/Multiplexer with 3-State Outputs |
| Technology Family | ALS (Advanced Low-Power Schottky TTL) |
| 通道數 | 2 x 4:1 |
| 供應電壓 | 5 V (nominal) |
| 輸出類型 | 3-State |
| Output Control | Separate active-low OE per section |
| Select Inputs | 2 (common A, B) |
| 功能特色 | 3-state version of ALS153 / SN74AS153 |
| 工作溫度 | 0C to 70C (SN74 series) |
| Package Options | PDIP-16 (N), SOIC-16 (D), CERPACK (FK), CDIP (J) |
| 安裝類型 | Through Hole (N) / Surface Mount (D) |
| 腳位數 | 16 |
| Applications | Multiplexing from n lines to one line; parallel-to-serial conversion |
| Military Version | SN54ALS253 (J ceramic package) |
SN74ALS253 腳位配置
| 腳位 1 | OE1 — Output control 1 (active-low, 3-state enable) |
| 腳位 2 | B — Select input B (common, MSB) |
| 腳位 3 | 1C0 — Data input 1C0 |
| 腳位 4 | 1C1 — Data input 1C1 |
| 腳位 5 | 1C2 — Data input 1C2 |
| 腳位 6 | 1C3 — Data input 1C3 |
| 腳位 7 | 1Y — 3-state output 1Y |
| 腳位 8 | GND — Ground |
| 腳位 9 | 2Y — 3-state output 2Y |
| 腳位 10 | 2C0 — Data input 2C0 |
| 腳位 11 | 2C1 — Data input 2C1 |
| 腳位 12 | 2C2 — Data input 2C2 |
| 腳位 13 | 2C3 — Data input 2C3 |
| 腳位 14 | A — Select input A (common, LSB) |
| 腳位 15 | OE2 — Output control 2 (active-low, 3-state enable) |
| 腳位 16 | VCC — Supply voltage (5 V nominal) |
典型應用
SN74ALS253 適用於 6 應用s: Bus-Organized System Data Selection, Parallel-to-Serial Data Conversion, Legacy TTL System Maintenance and Repair, Multiplexing n Lines to One Line, Data-Acquisition Front-End Channel Selection, Address and Control-Word Selection in Industrial Controllers.
Bus-Organized System Data Selection
The SN74ALS253 is purpose-built for bus-organized systems where its 3-state outputs interface with and drive shared data lines, per the TI datasheet. Each section's independent active-low OE allows both mux halves to time-share one bus line: one drives while the other floats in high impedance. The ALS drive capability maintains solid logic levels across typical TTL bus loading, and the fast ALS propagation keeps bus turnaround glitches short. Decoupling and controlled bus capacitance (kept within TTL derating limits) are the main performance considerations.
推薦
Parallel-to-Serial Data Conversion
The datasheet explicitly cites parallel-to-serial conversion as a primary application: stepping the common select inputs A and B through binary sequence 00, 01, 10, 11 serializes one 4-bit word per mux. The ALS family speed ensures each channel settles well within typical counter-clock periods, while the 3-state output gates the data stream onto a shared line. Using a 2-bit binary counter (e.g., 74HC163 family) to drive the select lines yields a clean, glitch-minimized serial data stream for telemetry or legacy serial links.
推薦
Legacy TTL System Maintenance and Repair
Repairing 1980s-1990s industrial controllers, test equipment, and minicomputer boards often requires exact ALS-family devices to preserve timing margins designed around ALS propagation delay and supply current. The SN74ALS253 drops onto original 16-pin DIP footprints with no PCB rework. Where ALS stock is exhausted, LS or AS variants in the same pinout keep systems running, though timing verification against the original design's worst-case paths is recommended when substituting across TTL subfamilies.
推薦
Multiplexing n Lines to One Line
The datasheet notes the SN74ALS253 permits multiplexing from n lines to one line by cascading multiple devices whose 3-state outputs share a common line, with each device enabled in turn via its OE control. Two devices give 8-to-1 selection, four give 16-to-1, and so on. ALS propagation delay of each level remains short, so enable decode adds minimal latency. This topology is common in legacy data-acquisition front ends routing multiple sensor channels to a single ADC input stage.
推薦
Data-Acquisition Front-End Channel Selection
In legacy instrumentation, the SN74ALS253 selects among up to eight analog-conditioned logic-level channels feeding comparators or digital sampling stages, with the 3-state output isolating inactive sections from the shared sense line. Its separate OE per half enables redundant-channel architectures where a backup mux takes over seamlessly. Because it is a digital mux, signals must be logic-level; for true analog switching, an analog multiplexer such as the CD4052 or MPC506 is the appropriate companion or substitute.
推薦
Address and Control-Word Selection in Industrial Controllers
Industrial PLC I/O boards of the ALS era used dual 4:1 muxes to choose between local and remote address or control-word sources, selected by a mode line driving the OE inputs. The SN74ALS253's independent output controls make source-switchover glitch-manageable, and its TTL thresholds interface directly with bipolar-era controller logic. The ALS low supply current relative to LS reduced backplane power budgets. Modern retrofits should confirm 5V availability and consider HC253 substitutes if timing margins permit.
推薦
推薦產品摘要
工程參考資料，適用於 SN74ALS253 — 比較、設計指引及合規資訊。
選型指南
與替代品比較
| 參數 | 本產品 | SN74AS253A | SN74LS253 | SN74HC253 | CD74HC253 |
|---|---|---|---|---|---|
| Package | PDIP-16 (N) / SOIC-16 (D) | PDIP-16 (N) / SOIC-16 (D) - same | PDIP-16 (N) - same | PDIP-16 (N) / SOIC-16 (D) - same | PDIP-16 (N) / SOIC-16 (D) - same |
| Brand | Texas Instruments | Texas Instruments | Texas Instruments | Texas Instruments | Renesas Electronics |
| Technology Family | ALS TTL | AS TTL | LS TTL | HC CMOS | HC CMOS |
| Function | Dual 4:1 mux, 3-state outputs | Dual 4:1 mux, 3-state outputs | Dual 4:1 mux, 3-state outputs | Dual 4:1 mux, 3-state outputs | Dual 4:1 mux, 3-state outputs |
| Supply Voltage (nominal) | 5 V | 5 V | 5 V | 2 V to 6 V | 2 V to 6 V |
| Relative Supply Current | Low-moderate (ALS) | High (AS) | Moderate (LS) | Very low (CMOS) | Very low (CMOS) |
| Lifecycle Status | Obsolete | Obsolete/EOL | Obsolete/EOL | Active | Active |
主要差異化特點
- ALS speed-power advantage (對比SN74LS253)
- Independent 3-state control per section (對比SN74LS153)
- Exact legacy timing fidelity (對比SN74HC253)
設計說明
Power the SN74ALS253 from a regulated 5V supply (TTL 4.75V-5.25V recommended range per ALS family conventions). Place a 0.1uF ceramic decoupling capacitor within a few millimeters of the VCC pin; bipolar TTL draws transient current spikes on output transitions, so also include bulk 10uF local capacitance for boards with multiple ALS devices. CMOS substitutes (74HC253) tolerate 2V-6V but check threshold compatibility with surrounding TTL logic before changing families.
When a 3-state output is disabled (OE high), the shared bus line floats and can oscillate or pick up noise. Add a pull-up or pull-down resistor (e.g., 4.7k to 10k) on bus lines that may be undriven, or use bus-hold logic if available. Keep bus stubs short; ALS transition times are fast enough that long unterminated bus runs exhibit reflections visible as glitches at receiver inputs.
Do not confuse the OE polarity: both output controls are active-LOW (outputs enabled when OE = L). Driving OE from a reset controller that asserts high will leave both mux outputs disabled at power-up. Also, select inputs A and B are common to both sections; per-section selection is not possible. When substituting CMOS HC253 for ALS in repairs, verify propagation delay against the original system's setup/hold budget before committing.
合規資訊
Obsolete bipolar TTL part predating modern compliance documentation; ceramic (J/FK) package options historically contained lead. Verify with TI product page or broker for specific date codes.
