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Texas Instruments SN74ALS137AD
- Part No.:
- SN74ALS137AD
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
SN74ALS137AD.pdf
- Description:
- IC DECODER/DEMUX 1X3:8 16SOIC
- Quantity:
- Payment:
- Shipping:
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Product details
Overview
SN74ALS137AD from Texas Instruments is a 3-line to 8-line decoder/demultiplexer with integrated 3-bit address latch and dual output enables (G1, G2). It operates at 4.5–5.5 V, delivers 4 mA low-level output drive, supports 0°C to 70°C operation, and features glitch-free strobed-address decoding for bus-oriented systems.
For engineers reviewing the SN74ALS137AD datasheet, SN74ALS137AD pinout, SN74ALS137AD application, or SN74ALS137AD equivalent, key selection criteria include latch-enable timing (tsu = 10 ns), propagation delay (tPLH/tPHL ≤ 20 ns), output enable independence, and SOIC-16 package compatibility in legacy industrial control and memory address decoding designs.
Technical Context
This device implements positive-logic decoding with latched address inputs (A, B, C) controlled by LE, enabling stable output selection during address transitions. Output states are independently gated by active-low G1 and active-high G2 - both must be asserted (G1 = H, G2 = L) for valid Y0–Y7 outputs.
The SN74ALS137AD uses ALS (Advanced Low-Power Schottky) bipolar technology, delivering higher speed than standard LS while maintaining TTL-compatible voltage thresholds (VIH = 2 V, VIL = 0.8 V) and 5-V supply operation. All outputs are totem-pole, not open-collector, and drive high/low actively without external pull-ups.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | 3-to-8 decoder with transparent latch and dual output enables - enables stored-address decoding without output glitches during bus arbitration. |
| Supply Voltage | 4.5 V to 5.5 V - compatible with standard 5-V TTL logic rails; absolute max 7 V prevents damage during transient overvoltage. |
| Output Drive | IOL = 4 mA (min), IOH = −0.4 mA - sufficient to directly drive multiple TTL inputs or small capacitive loads (<50 pF) without buffering. |
| Propagation Delay | tPLH/tPHL ≤ 20 ns (A/B/C → Y, VCC = 4.5–5.5 V, CL = 50 pF) - supports >25 MHz address strobe rates in synchronous bus systems. |
| Latch Timing | tsu = 10 ns (A/B/C before LE↑), th = 5 ns (after LE↑) - defines minimum setup window for reliable address capture in strobed control logic. |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade embedded systems, not extended industrial or automotive environments. |
| Logic Family | ALS (Advanced Low-Power Schottky) - provides 2× speed vs. standard LS with comparable power (ICC = 5–11 mA typical). |
Pinout & Package
SN74ALS137AD is supplied in a 16-pin SOIC (D) package, 300-mil width, with gull-wing leads and standard JEDEC MO-012AC footprint. Pin 1 is marked with a notch or dot; pin numbering follows counterclockwise convention from top-left corner.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (G2) | Active-high output enable | When high, forces all outputs Y0–Y7 high regardless of select or latch state - used for hierarchical enable/disable in multi-device decode trees. |
| 2 (G1) | Active-low output enable | When low, enables output drivers only if G2 is also low - dual-enable architecture allows independent gating of decoder sections. |
| 3 (C) | Most-significant address input | Third bit of 3-bit binary address (CBA); latched on LE rising edge - determines Y4–Y7 vs. Y0–Y3 group selection. |
| 4 (B) | Mid-significance address input | Second bit of address; sampled and held with A and C - forms full 3-bit latch for static output selection. |
| 5 (A) | Least-significant address input | First bit of address; synchronized to LE edge - eliminates race conditions between address change and output update. |
| 6 (Y0) | Active-low decoded output | Asserted low when latched address = 000₂ and G1/G2 enabled - drives one of eight mutually exclusive device selects or memory chip enables. |
| 7 (Y1) | Active-low decoded output | Asserted low when latched address = 001₂ - each Yx corresponds to unique 3-bit code; all others remain high. |
| 8 (Y2) | Active-low decoded output | Asserted low when latched address = 010₂ - outputs are fully decoded and non-overlapping; no shared enable required per output. |
| 9 (Y3) | Active-low decoded output | Asserted low when latched address = 011₂ - supports direct connection to chip-select lines of peripheral ICs without inversion logic. |
| 10 (Y4) | Active-low decoded output | Asserted low when latched address = 100₂ - enables 1-of-8 decoding for I/O port expansion or interrupt vector routing. |
| 11 (Y5) | Active-low decoded output | Asserted low when latched address = 101₂ - all eight outputs available simultaneously; no internal multiplexing or time-division. |
| 12 (Y6) | Active-low decoded output | Asserted low when latched address = 110₂ - supports memory-mapped peripheral addressing where each device occupies unique 1-byte or 1-word space. |
| 13 (Y7) | Active-low decoded output | Asserted low when latched address = 111₂ - final output completes full 3-bit decode space; complements address latch function. |
| 14 (NC) | No internal connection | Unbonded pad; must remain unconnected - no routing, grounding, or pulling required; avoids unintended parasitic coupling. |
| 15 (LE) | Latch-enable control | Rising-edge triggered; captures A/B/C values at transition - enables synchronous address sampling aligned to system clock or strobe signal. |
| 16 (VCC) | Positive supply | +5 V nominal power rail; decoupling capacitor (0.1 µF) required within 1 cm for stable switching performance. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated 3-bit address latch | Eliminates need for external D-latches in strobed address decode paths - reduces component count and board area in bus interface logic. |
| Dual independent output enables | G1 (active-low) and G2 (active-high) allow hierarchical enable tree construction - simplifies cascading across multiple SN74ALS137AD devices for 1-of-16 or larger decode. |
| Glitch-free output behavior | Latched address prevents momentary invalid outputs during address transitions - critical for reliable chip-select generation in shared-bus microprocessor systems. |
| ALS bipolar process | Delivers 20 ns max propagation delay with 11 mA max ICC - achieves speed/power balance superior to standard LS while retaining TTL voltage compatibility. |
| TTL-compatible input thresholds | VIH = 2 V min, VIL = 0.8 V max - ensures interoperability with 74LS, 74F, and microcontroller GPIO without level-shifting circuitry. |
Applications
| Memory Address Decoding | Peripheral Select Logic |
|---|---|
|
Use Scenario: Microprocessor-based system with 8-bit data bus and 16-bit address bus requires discrete decoding of upper address bits to select RAM, ROM, and I/O chips. IC Role / Device Role / Timing Role: SN74ALS137AD latches A13–A15 and decodes them into eight independent chip-select signals (CS0–CS7), synchronized to WR or MREQ strobe. Use Value: Eliminates race conditions between address settling and CS assertion, ensuring reliable memory access timing without added wait states. |
Use Scenario: Industrial PLC backplane with modular I/O cards needs dedicated select lines for up to eight analog input modules. IC Role / Device Role / Timing Role: SN74ALS137AD acts as central address decoder, using module slot ID (A0–A2) and backplane enable to assert individual module enables. Use Value: Provides deterministic, non-glitching enable timing across all modules - prevents spurious register reads/writes during hot-swap or configuration changes. |
| Bus-Oriented Strobed Control | Legacy System Address Expansion |
|
Use Scenario: Vintage computer design (e.g., Z80-based) requires synchronized address latching for DMA controller or video display list addressing. IC Role / Device Role / Timing Role: SN74ALS137AD captures address on rising edge of DMA acknowledge (LE), then decodes to select VRAM page or I/O register bank. Use Value: Enables precise timing alignment between bus master handshaking and peripheral selection - critical for cycle-accurate video timing generation. |
Use Scenario: Retrofit upgrade of 1980s instrumentation system adds new sensor interface cards requiring additional address space beyond original decoder capability. IC Role / Device Role / Timing Role: SN74ALS137AD cascades with existing 74LS138 via G1/G2 enables to expand from 1-of-8 to 1-of-16 decoding without redesigning control logic. Use Value: Maintains backward compatibility while adding new hardware - leverages pinout and timing equivalence to minimize PCB rework. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar 3-to-8 decoder-with-latch applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS138N | No internal latch; requires external latch or synchronous address bus - lacks LE input and transparent latch functionality. | Suitable only where address is stable prior to enable assertion; cannot support strobed or asynchronous address capture. | Select SN74ALS138N only if system already provides latched address signals - avoids redundant latch logic but loses SN74ALS137AD's integrated timing control. |
| SN74AS137N | Faster propagation delay (12.5 ns max vs. 20 ns), higher ICC (15–24 mA), and stronger drive (IOL = 20 mA) - AS family trade-off: speed vs. power. | Better suited for high-speed bus systems (>40 MHz strobe rates) where timing margin is critical and power budget allows. | Choose SN74AS137N when SN74ALS137AD's 20 ns delay is insufficient - verify thermal management and supply regulation for doubled current draw. |
Compared with SN74ALS137AD, SN74ALS138N removes latch functionality entirely - requiring external synchronization - while SN74AS137N retains identical pinout and logic but trades 2× speed for 2× power consumption and reduced noise margin.
Availability
SN74ALS137AD is available at Aetrix Electronics and suitable for legacy system repair, industrial control retrofitting, and educational electronics labs requiring stable component supply of discontinued yet widely documented TTL logic.
Supply support for SN74ALS137AD 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 solutions with broad industrial and automotive reach.
The SN74ALS137AD belongs to TI's legacy ALS logic family, designed specifically for high-reliability, medium-speed digital control systems where latch-synchronized decoding and TTL compatibility were essential design requirements.
FAQ
What is the operating temperature range for SN74ALS137AD?
The SN74ALS137AD is characterized for operation from 0°C to 70°C - this commercial-grade range aligns with standard office and indoor industrial environments. It is not rated for extended temperature operation like the military-grade SN54ALS137A (−55°C to 125°C), and thermal derating is not supported beyond the specified limits. Always maintain ambient PCB temperature within this window during continuous operation.
Does SN74ALS137AD have open-collector outputs?
No, SN74ALS137AD features totem-pole (push-pull) outputs - each Y0–Y7 actively drives high or low without requiring external pull-up resistors. This differs from open-collector variants like the 74ALS138, which mandate external pull-ups for wired-AND operation. The SN74ALS137AD's outputs are TTL-compatible and designed for direct connection to standard logic inputs.
Can SN74ALS137AD replace SN74LS137 in an existing design?
Yes, SN74ALS137AD is a direct functional and pin-compatible upgrade to SN74LS137 - it shares identical pinout, logic function, and DC specifications (VIH/VIL, VOH/VOL), while offering faster propagation delay (20 ns vs. 30 ns typical) and lower power (ICC ≈ 8 mA vs. 15 mA). No PCB changes are needed, but verify timing margins with the improved speed.
What happens to outputs when G1 is low and G2 is high?
When G1 is low and G2 is high, all outputs Y0–Y7 are forced high regardless of latch state, address inputs, or LE condition - this is defined in the function table as a global disable state. This behavior allows safe, simultaneous deactivation of all downstream devices during reset or power-up sequencing without relying on address stability.
Is SN74ALS137AD still in active production?
No, SN74ALS137AD is marked "Obsolete" by Texas Instruments per official packaging documentation. However, Aetrix Electronics maintains verified, traceable inventory sourced from authorized legacy channels, supporting long-term maintenance of deployed systems where redesign is impractical or cost-prohibitive.
SN74ALS137AD Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 16-SOIC (0.154", 3.90mm Width)
- Packaging:
- Bulk
- Product Status:
- Obsolete
- Type:
- Decoder/Demultiplexer
- Circuit:
- 1 x 3:8
- Independent Circuits:
- 1
- Current - Output High, Low:
- 400µA, 8mA
- Voltage Supply Source:
- Single Supply
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SOIC
SN74ALS137AD FAQ
1.How can I place an order for SN74ALS137AD through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS137AD on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for SN74ALS137AD reliable?
The price and inventory of SN74ALS137AD are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS137AD is usually 5 days.
3.What payment methods are accepted for SN74ALS137AD?
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Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS137AD?
SN74ALS137AD orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS137AD order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for SN74ALS137AD?
For technical support, including SN74ALS137AD datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS137AD requirements.
6.How does Aetrix verify that SN74ALS137AD is sourced from the original manufacturer or authorized distributors?
All SN74ALS137AD products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that SN74ALS137AD meets industry standards.
7.What is the process for return or replacement of SN74ALS137AD?
All SN74ALS137AD units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS137AD, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The SN74ALS137AD part is unused and in its original packaging.
Return procedure for SN74ALS137AD:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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