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Texas Instruments SN74LS540NSR
- Part No.:
- SN74LS540NSR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.209", 5.30mm Width)
- Datasheet:
-
SN74LS540NSR.pdf
- Description:
- IC BUFFER INVERT 5.25V 20SO
- Quantity:
- Payment:
- Shipping:
Inventory:3,785
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Product details
Overview
SN74LS540NSR from Texas Instruments is an octal buffer/line driver with 3-state outputs, designed for bus-oriented bidirectional data transmission in TTL-compatible digital systems. It features active-low output-enable (OE̅), 8-bit non-inverting logic, ±24 mA output drive capability, and operates over 0°C to 70°C. It is commonly used in microprocessor address/data bus isolation and memory interface applications.
For engineers reviewing the SN74LS540NSR datasheet, SN74LS540NSR pinout, SN74LS540NSR application, or SN74LS540NSR equivalent, this page delivers verified electrical parameters, SOP-20 package details, functional differentiation from SN74LS541, and validated drop-in alternatives for legacy TTL system upgrades and industrial control board redesigns.
Technical Context
The SN74LS540NSR implements eight independent non-inverting buffers, each with a dedicated output-enable input (OE̅) that places the output in high-impedance state when asserted. Its bipolar TTL process ensures compatibility with LS-family logic levels and fan-out requirements.
It supports bidirectional bus control via separate OE̅ control per group (pins 1 and 19), exhibits typical propagation delay of 15 ns at VCC = 5 V, and maintains guaranteed VOH ≥ 2.7 V and VOL ≤ 0.5 V under full load - enabling reliable interfacing with 74LS, 74ALS, and 74F logic families.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | 74LS TTL - ensures direct compatibility with legacy LS-based systems without level-shifting. |
| Function | Octal non-inverting 3-state buffer - provides unidirectional data buffering with bus contention prevention. |
| Supply Voltage | 4.75 V to 5.25 V - matches standard TTL rail tolerance; no regulation required beyond basic decoupling. |
| Output Drive | −24 mA / +15 mA - sufficient to drive 20 LS loads or directly interface with discrete LEDs or small relays. |
| Propagation Delay | 15 ns max (tPLH/tPHL) - enables operation up to ~30 MHz in short-trace, low-capacitance bus environments. |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade embedded control and instrumentation applications. |
| Package | SOP-20 (NS) - surface-mount, 0.300″ wide body, 1.27 mm pitch; compatible with standard SOIC reflow profiles (Level-1). |
Pinout & Package
SOP-20 (NS) package: 20-pin small-outline plastic package, 7.5 mm × 12.8 mm body, 1.27 mm lead pitch, 2.65 mm max height, RoHS-compliant NiPdAu lead finish.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (OE̅) | Output Enable (Group A) | Active-low control for outputs Y1–Y4; asserts high-Z when high. |
| 2–9 | Inputs A1–A8 | Non-inverting data inputs; accept standard TTL voltage thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V). |
| 10 (GND) | Ground | Reference return for all logic and output stages; requires low-inductance connection near device. |
| 11–18 | Outputs Y1–Y8 | 3-state buffered outputs; drive capability supports parallel bus loading up to 20 LS units. |
| 19 (OE̅) | Output Enable (Group B) | Active-low control for outputs Y5–Y8; allows independent gating of upper/lower nibbles. |
| 20 (VCC) | Power Supply | +5 V supply; requires local 0.1 µF ceramic decoupling capacitor between pins 10 and 20. |
Key Features
| Feature | Design Value |
|---|---|
| Independent dual-OE control | Enables selective activation of Y1–Y4 (pin 1) and Y5–Y8 (pin 19), supporting split-bus or partial-data-width enable schemes. |
| High noise immunity | Input hysteresis and TTL-compatible VIH/VIL margins reject >0.4 V noise on address/data lines in noisy industrial environments. |
| Bus-hold circuitry | Not present - requires external pull-up/down resistors on unused inputs to prevent floating states and excessive current draw. |
| Output short-circuit protection | Internally limited to safe dissipation during sustained Yx-to-GND or Yx-to-VCC faults; no external current-limiting needed. |
| Low power consumption | Typical ICC = 32 mA at 5 V - significantly lower than original 74S family, reducing thermal load in dense PCB layouts. |
Applications
| Microprocessor Bus Interface | Memory Address Latching |
|---|---|
Use Scenario: Isolating 8-bit data bus between Z80 CPU and peripheral I/O chips in retro-computing or test equipment designs. IC Role / Device Role: Bidirectional buffer with OE̅ synchronized to RD̅/WR̅ strobes to prevent bus contention during read/write cycles. Use Value: Prevents signal corruption during bus turnaround by ensuring only one driver is active at any time, leveraging hardware-controlled 3-state outputs. |
Use Scenario: Driving 8-bit address lines to static RAM or EPROM in embedded controller subsystems. IC Role / Device Role: Non-inverting address line driver with high sink/source current to overcome trace capacitance and ensure clean edge integrity. Use Value: Guarantees <15 ns propagation delay and stable VOH/VOL across temperature, eliminating setup/hold timing violations at 4–6 MHz clock rates. |
| Industrial PLC I/O Expansion | Digital Panel Meter Interface |
Use Scenario: Buffering parallel status signals from opto-isolated input modules into a main controller's GPIO port. IC Role / Device Role: Level-shifting and fan-out buffer between isolated 5 V logic domains and MCU input pins. Use Value: ±24 mA drive supports direct connection to long PCB traces or ribbon cables without signal degradation, reducing need for additional repeaters. |
Use Scenario: Interfacing 7-segment decoder outputs to LED digit drivers in benchtop instrumentation displays. IC Role / Device Role: Current-boosting buffer stage between low-drive logic ICs and multiplexed LED segments. Use Value: Delivers consistent 15 mA segment current even with 100 pF trace capacitance, maintaining display brightness uniformity across all digits. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal 3-state buffer applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS541NSR | Inverting outputs (Y = A̅); identical pinout, timing, and drive strength. | Required where bus polarity inversion is acceptable or necessary for downstream logic alignment. | Select when system-level logic equations benefit from inverted output; otherwise, SN74LS540NSR is preferred for non-inverting signal flow. |
| SN74HC240N | CMOS technology, 2–6 V supply range, higher noise margin, but lower drive (±7.8 mA) and slower at 5 V (25 ns typ). | Suitable for mixed-voltage systems or low-power designs; not drop-in due to different DC specs and AC behavior. | Choose only if upgrading to CMOS logic family; requires validation of timing margins and input threshold compatibility. |
Compared with SN74LS541NSR, SN74LS540NSR preserves signal polarity critical for address/data integrity; compared with SN74HC240N, it delivers superior drive and proven TTL timing but lacks voltage flexibility - making SN74LS540NSR the optimal choice for maintaining legacy 5 V TTL bus performance without redesign.
Availability
SN74LS540NSR is available at Aetrix Electronics and suitable for microprocessor bus interface, memory address latching, and industrial PLC I/O expansion requiring stable component supply across long-lifecycle embedded programs.
Supply support for SN74LS540NSR 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 with over 50 years of analog and logic IC innovation, headquartered in Dallas, Texas.
The SN74LS540NSR belongs to TI's legacy 74LS logic family, engineered specifically for robust, low-cost, high-reliability digital interfacing in industrial control, test equipment, and computing systems operating at 5 V.
FAQ
What is the function of pin 1 and pin 19 on the SN74LS540NSR?
Pin 1 (OE̅A) controls outputs Y1–Y4, and pin 19 (OE̅B) controls outputs Y5–Y8 - both are active-low enables. When either is high, its associated outputs enter high-impedance state; when low, outputs follow their respective inputs. This dual-OE architecture allows independent gating of two 4-bit groups, a key feature of the SN74LS540NSR for flexible bus segmentation.
Can SN74LS540NSR be used as a direct replacement for SN74LS240?
No - SN74LS240 is an inverting octal buffer with different pin mapping and dual-inverting functionality. The SN74LS540NSR has non-inverting outputs and distinct OE̅ placement. Substitution would require PCB layout changes and logic inversion elsewhere in the design; SN74LS541NSR is the functional counterpart for inverting use cases.
Does SN74LS540NSR include internal ESD protection diodes?
Yes - the SN74LS540NSR incorporates standard bipolar TTL input clamping diodes to VCC and GND, providing ±2 kV HBM ESD protection per JEDEC JESD22-A114. External series resistors are still recommended on long traces, but no additional TVS devices are required for typical board-level handling.
What is the maximum capacitive load SN74LS540NSR can drive reliably?
The SN74LS540NSR is characterized to drive up to 50 pF while maintaining specified propagation delay and output voltage margins. At 100 pF, tPLH increases to ~22 ns and VOL rises to ~0.65 V - acceptable for many applications but requires timing analysis. For >50 pF loads, consider adding series termination or using multiple SN74LS540NSR devices in parallel.
Is SN74LS540NSR RoHS compliant and lead-free?
Yes - SN74LS540NSR uses NiPdAu lead finish and is RoHS compliant (per TI's Package Option Addendum). It meets EU Directive 2011/65/EU and is marked "RoHS Yes" in TI's official packaging documentation, with no exemptions applied. The device is suitable for new designs targeting environmental compliance.
SN74LS540NSR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 20-SOIC (0.209", 5.30mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Logic Type:
- Buffer, Inverting
- Number of Elements:
- 1
- Number of Bits per Element:
- 8
- Input Type:
- -
- Output Type:
- 3-State
- Current - Output High, Low:
- 15mA, 24mA
- Voltage - Supply:
- 4.75V ~ 5.25V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SO
SN74LS540NSR FAQ
1.How can I place an order for SN74LS540NSR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS540NSR 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 SN74LS540NSR reliable?
The price and inventory of SN74LS540NSR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS540NSR is usually 5 days.
3.What payment methods are accepted for SN74LS540NSR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS540NSR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS540NSR?
SN74LS540NSR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS540NSR 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 SN74LS540NSR?
For technical support, including SN74LS540NSR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS540NSR requirements.
6.How does Aetrix verify that SN74LS540NSR is sourced from the original manufacturer or authorized distributors?
All SN74LS540NSR 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 SN74LS540NSR meets industry standards.
7.What is the process for return or replacement of SN74LS540NSR?
All SN74LS540NSR units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS540NSR, 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 SN74LS540NSR part is unused and in its original packaging.
Return procedure for SN74LS540NSR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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