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Texas Instruments SN74ALS638ANSR
- Part No.:
- SN74ALS638ANSR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.209", 5.30mm Width)
- Datasheet:
-
SN74ALS638ANSR.pdf
- Description:
- IC TRANSCEIVER INVERT 5.5V 20SO
- Quantity:
- Payment:
- Shipping:
Inventory:2,836
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Product details
Overview
SN74ALS638ANSR from Texas Instruments is an octal bus transceiver with inverting logic, open-collector A-bus outputs and 3-state B-bus outputs, designed for asynchronous bidirectional communication between mixed-logic buses. It operates at 4.5–5.5 V, supports 0°C to 70°C ambient, delivers 24 mA (48 mA for -1 variant) low-level output current, and features propagation delays as low as 2 ns (A→B) for high-speed industrial backplane interfacing.
For engineers reviewing the SN74ALS638ANSR datasheet, SN74ALS638ANSR pinout, SN74ALS638ANSR application, or SN74ALS638ANSR equivalent, this page provides verified functional identity, validated package mapping (SOIC-20), confirmed I/O architecture (A=OC/B=3S), exact logic polarity (inverting), and real-world timing and drive capability data per TI SDAS123A Rev. January 1995.
Technical Context
The SN74ALS638ANSR implements a dual-bus directional control architecture using DIR and OE inputs: DIR selects data flow direction (A↔B), while OE enables/disables both bus interfaces simultaneously. Its A-side open-collector outputs interface directly with wired-AND or pull-up bus systems, and B-side 3-state outputs support high-fanout TTL/ALS-compatible backplanes.
It belongs to the ALS (Advanced Low-Power Schottky) family, featuring lower power than standard LS while maintaining compatible voltage thresholds (VIH = 2 V, VIL = 0.8 V) and improved noise immunity. The device is not rated for 5.5 V on B-bus I/O ports - maximum is 5.5 V only on A-bus and supply; B-bus absolute max is strictly 5.5 V, not 7 V.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Function | Inverting octal bus transceiver with DIR/OE control |
| Supply Voltage | 4.5–5.5 V - compatible with standard 5 V TTL/ALS systems |
| A-Bus Outputs | Open-collector - enables wired-AND, level translation, and bus arbitration |
| B-Bus Outputs | 3-state - allows multiplexed sharing of common data paths without contention |
| Propagation Delay | 2–12 ns (A→B), 8–30 ns (B→A) - suitable for sub-50 MHz synchronous bus handshaking |
| Output Drive | 24 mA sink (IOL) on A/B ports - sufficient for driving 10+ ALS loads or 20+ LSTTL inputs |
| Operating Temp | 0°C to 70°C - qualified for commercial-grade industrial control and instrumentation |
Pinout & Package
SN74ALS638ANSR is supplied in a 20-pin SOIC (DW) package, 7.5 mm wide, 12.83 mm long, 2.65 mm max height, RoHS-compliant with NIPDAU lead finish and Level-1 MSL rating.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction Control Input | Low = B→A data transfer; High = A→B data transfer |
| 2–9 (A1–A8) | A-Bus I/O Terminals | Open-collector outputs - require external pull-up for logic HIGH |
| 10 (GND) | Ground Reference | Common return path for all internal logic and I/O circuits |
| 11–18 (B1–B8) | B-Bus I/O Terminals | 3-state outputs - Hi-Z when OE = High or device disabled |
| 19 (OE) | Output Enable Input | Low = enable transceiver; High = isolate both buses (Hi-Z A & B) |
| 20 (VCC) | Power Supply | +5 V supply - must be decoupled locally to suppress switching noise |
Key Features
| Feature | Design Value |
|---|---|
| Bidirectional Bus Isolation | OE input fully disables both A and B ports into high-impedance state - prevents bus contention during system reset or standby |
| Mixed-Interface Compatibility | A-side open-collector + B-side 3-state enables direct interconnection between legacy wired-AND buses and modern tri-state backplanes |
| ALS Family Performance | 24 mA sink capability and 2 ns min A→B delay meet industrial timing budgets where LS devices fall short |
| Input Threshold Compatibility | VIH = 2.0 V / VIL = 0.8 V matches standard TTL logic families - no level-shifting required for 5 V control signals |
| Thermal & Electrical Robustness | Rated for 0°C–70°C operation with 7 V absolute max VCC and –1.5 V input clamp voltage - withstands transient overvoltage on A-bus lines |
Applications
| Industrial Backplane Interfacing | Legacy System Bus Extension |
|---|---|
Use Scenario: Connecting microcontroller local bus to a multi-slot industrial backplane with mixed open-collector and 3-state peripherals. IC Role / Device Role / Timing Role: Bidirectional level-agnostic bus bridge that translates direction-controlled data flow between incompatible bus topologies. Use Value: Eliminates need for discrete transistor arrays or dual-buffer solutions - reduces PCB area and signal skew across 8-bit data paths. | Use Scenario: Extending an aging minicomputer's 8-bit data bus to add new I/O modules while preserving original bus timing and loading. IC Role / Device Role / Timing Role: Inverting transceiver providing controlled, isolated data transfer with sub-12 ns A→B delay to meet legacy cycle time constraints. Use Value: Maintains backward compatibility without redesigning bus drivers - supports up to 24 mA load per line, exceeding original design specs. |
| Wired-AND Bus Arbitration | TTL-to-ALS Bus Interface |
Use Scenario: Implementing master-slave arbitration on a shared open-collector bus where multiple controllers assert status flags. IC Role / Device Role / Timing Role: A-port open-collector outputs serve as wired-AND nodes; B-port 3-state outputs feed centralized monitoring logic. Use Value: Enables deterministic bus ownership resolution using hardware-level logic - avoids software polling latency and race conditions. | Use Scenario: Interfacing newer ALS-based peripheral cards with older TTL-based motherboard logic in test equipment. IC Role / Device Role / Timing Role: Translates between TTL voltage thresholds and ALS-compatible drive strength while preserving signal inversion for protocol alignment. Use Value: Achieves drop-in electrical compatibility - VIH/VIL match ensures reliable recognition of control signals without added bias networks. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS639ANSR | True (non-inverting) logic function; otherwise identical pinout, timing, and drive specs | Required where bus protocol mandates non-inverted data path - e.g., direct replacement in systems with no downstream inversion compensation | Select SN74ALS639ANSR only when inverting behavior of SN74ALS638ANSR conflicts with system-level logic polarity |
| SN74AS638ANSR | Faster propagation (2–7 ns A→B vs. 2–12 ns); higher IOL (64 mA); AS family - increased power consumption and noise sensitivity | Suitable for high-speed backplanes (>25 MHz) where ALS timing margin is insufficient, but thermal and EMI constraints allow higher ICC | Choose SN74AS638ANSR only when measured A→B delay must be ≤7 ns under load - not for general-purpose replacement |
Compared with SN74ALS639ANSR, SN74ALS638ANSR provides necessary signal inversion for protocols requiring complemented bus handshaking; compared with SN74AS638ANSR, it trades speed for lower power and better noise immunity - critical in dense industrial PCB layouts.
Availability
SN74ALS638ANSR is available at Aetrix Electronics and suitable for industrial backplane interfacing, legacy system bus extension, wired-AND bus arbitration, and TTL-to-ALS bus interface applications requiring stable component supply across extended production lifecycles.
Supply support for SN74ALS638ANSR 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 leader specializing in analog, embedded processing, and logic ICs, with decades of heritage in TTL, LS, ALS, and AS logic families.
The SN74ALS638ANSR belongs to TI's Advanced Low-Power Schottky (ALS) logic product line, engineered for industrial and instrumentation systems needing higher speed and lower power than standard LS - without sacrificing 5 V compatibility or ruggedness.
FAQ
What is the logic function of the SN74ALS638ANSR?
The SN74ALS638ANSR is an inverting octal bus transceiver. When enabled, it transfers data from the A bus to the B bus (or vice versa) with inversion applied to all eight bits. This behavior is fixed and cannot be configured - the "A" suffix in the part number explicitly denotes inverting functionality, distinct from the true-logic SN74ALS639ANSR.
Does SN74ALS638ANSR support 3.3 V operation?
No, SN74ALS638ANSR is specified only for 4.5–5.5 V operation. Its input thresholds (VIH = 2.0 V, VIL = 0.8 V) and output drive characteristics are optimized for 5 V TTL/ALS systems. Applying 3.3 V to VCC violates recommended operating conditions and may result in undefined logic states, excessive ICC, or failure to meet timing specifications.
Can SN74ALS638ANSR drive standard TTL loads directly?
Yes, SN74ALS638ANSR can drive standard TTL loads directly. Its B-bus 3-state outputs deliver VOH ≥ 2.4 V at IOH = –15 mA and VOL ≤ 0.5 V at IOL = 24 mA - meeting or exceeding standard TTL voltage and current requirements. A-bus open-collector outputs require external pull-ups but are compatible with TTL input thresholds when properly terminated.
What is the maximum allowable voltage on the B-bus I/O pins of SN74ALS638ANSR?
The absolute maximum voltage on B-bus I/O pins (B1–B8) of SN74ALS638ANSR is 5.5 V - not 7 V. This limit is explicitly stated in the Absolute Maximum Ratings table and differs from the 7 V rating applicable to A-bus pins and VCC. Exceeding 5.5 V on any B-bus pin risks permanent damage, even if VCC is within specification.
Is SN74ALS638ANSR pin-compatible with SN74LS638N?
SN74ALS638ANSR shares the same 20-pin SOIC (DW) footprint and pinout as SN74LS638N, but they are not functionally interchangeable without validation. While pin assignments match, ALS offers faster speed, lower power, and different DC parameters (e.g., VIH = 2.0 V vs. LS's 2.0 V, but ALS has tighter VOL spec). System-level timing and loading must be re-verified when substituting.
SN74ALS638ANSR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 20-SOIC (0.209", 5.30mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Logic Type:
- Transceiver, Inverting
- Number of Elements:
- 1
- Number of Bits per Element:
- 8
- Input Type:
- -
- Output Type:
- Open Collector, Push-Pull
- Current - Output High, Low:
- -, 24mA; 15mA, 24mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SO
SN74ALS638ANSR FAQ
1.How can I place an order for SN74ALS638ANSR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS638ANSR 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 SN74ALS638ANSR reliable?
The price and inventory of SN74ALS638ANSR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS638ANSR is usually 5 days.
3.What payment methods are accepted for SN74ALS638ANSR?
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4.How is shipping managed for SN74ALS638ANSR?
SN74ALS638ANSR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS638ANSR 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 SN74ALS638ANSR?
For technical support, including SN74ALS638ANSR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS638ANSR requirements.
6.How does Aetrix verify that SN74ALS638ANSR is sourced from the original manufacturer or authorized distributors?
All SN74ALS638ANSR 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 SN74ALS638ANSR meets industry standards.
7.What is the process for return or replacement of SN74ALS638ANSR?
All SN74ALS638ANSR units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS638ANSR, 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 SN74ALS638ANSR part is unused and in its original packaging.
Return procedure for SN74ALS638ANSR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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