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Texas Instruments SN74LS145N
- Part No.:
- SN74LS145N
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74LS145N.pdf
- Description:
- IC DECODER 1 X 4:10 16DIP
- Quantity:
- Payment:
- Shipping:
Inventory:383
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Product details
Overview
SN74LS145N from Texas Instruments is a TTL BCD-to-decimal decoder/driver IC in 16-pin PDIP package, operating from 4.75 V to 5.25 V, with typical propagation delay of 35 ns and output sink current capability of 40 mA per line. It drives common-anode LED displays directly in industrial control panels and legacy instrumentation systems.
For engineers reviewing the SN74LS145N datasheet, SN74LS145N pinout, SN74LS145N application, or SN74LS145N equivalent, key selection criteria include its open-collector outputs, BCD input compatibility, 0°C to 70°C commercial temperature range, and direct LED-driving capability without external transistors.
Technical Context
The SN74LS145N implements active-low decoded decimal outputs (Y0–Y9) driven by four binary-coded decimal inputs (A0–A3), with all ten outputs disabled when input code exceeds 9 (1010–1111). Its open-collector outputs allow wired-OR logic and direct interface to LEDs, relays, or lamps requiring high-sink drive.
It belongs to the 74LS logic family and uses bipolar Schottky transistor technology for improved speed-power trade-off over standard 74TTL. Input thresholds are compatible with LS-TTL voltage levels, and it requires no external pull-ups for basic decoding operation when used with current-limiting resistors on outputs.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | 74LS (Low-power Schottky TTL) - ensures compatibility with legacy TTL systems and predictable noise margins. |
| Supply Voltage | 4.75 V to 5.25 V - mandates regulated +5 V rail; not tolerant of undervoltage or overvoltage conditions. |
| Propagation Delay | 35 ns max (tPLH/tPHL) - supports synchronous decoding up to ~10 MHz clock rates in cascaded or gated applications. |
| Output Sink Current | 40 mA per output (min) - enables direct driving of standard LEDs (with series resistor) or small solenoids without buffer stages. |
| Input Compatibility | LS-TTL input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V) - interoperable with 74LS, 74ALS, and microcontroller GPIOs with 5 V logic levels. |
| Operating Temperature | 0°C to 70°C - rated for commercial-grade environments only; unsuitable for extended industrial or automotive under-hood use. |
Pinout & Package
SN74LS145N is housed in a 16-pin plastic dual in-line package (PDIP-N), 0.300-inch wide body, with standard through-hole mounting and 0.1-inch pin pitch. Pin 1 is marked by a notch or dot at the left end of the top edge.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (A3) | BCD input bit 3 (MSB) | Accepts high/low logic level to define most significant digit of 4-bit BCD code. |
| 2 (A2) | BCD input bit 2 | Second BCD weight (2² = 4); must be stable before enable conditions are met. |
| 3 (A1) | BCD input bit 1 | Third BCD weight (2¹ = 2); part of synchronous input set determining active output line. |
| 4 (A0) | BCD input bit 0 (LSB) | Least significant BCD bit (2⁰ = 1); completes 4-bit code that selects one of ten outputs. |
| 5–6, 8–11 (Y0–Y9) | Active-low decoded outputs | Open-collector outputs; each sinks current when corresponding BCD value is present (e.g., A3–A0 = 0000 → Y0 low). |
| 7 (GND) | Ground reference | Return path for all internal logic and output sink currents; must be low-impedance connection. |
| 12–14, 16 (NC) | No-connect terminals | Internally unconnected; must remain unconnected on PCB to avoid parasitic coupling or ESD paths. |
| 15 (VCC) | Positive supply | +5 V DC power input; requires local 0.1 µF ceramic decoupling capacitor placed within 1 cm. |
Key Features
| Feature | Design Value |
|---|---|
| Open-collector outputs | Enable wired-OR logic, level translation to higher voltages (e.g., 12 V lamps), and direct LED drive with single series resistor per segment. |
| BCD input validation | Outputs Y0–Y9 go high-impedance for invalid codes (10–15), preventing false activation in noisy or misaligned data streams. |
| High sink current per output | 40 mA rating allows driving multiple parallel LEDs or electromechanical indicators without external drivers, reducing BOM count. |
| Standard 74LS timing | 35 ns propagation delay ensures synchronization with other 74LS devices in legacy digital systems without added wait states. |
Applications
| Industrial Panel Meters | Legacy Test Equipment Displays |
|---|---|
Use Scenario: Driving 7-segment or discrete LED arrays in analog-to-digital panel meters with manual BCD output from ADC or counter ICs. IC Role / Device Role / Timing Role: BCD-to-decimal decoder translating 4-bit digital values into individual digit-enable lines for multiplexed or static LED display control. Use Value: Eliminates need for discrete transistor arrays or additional logic gates, lowering system cost and board space in fixed-function instrumentation. | Use Scenario: Controlling indicator lamps on benchtop oscilloscopes, function generators, or logic analyzers where status or mode selection is encoded in BCD. IC Role / Device Role / Timing Role: Active-low driver enabling visual feedback for channel selection, trigger mode, or calibration state via dedicated lamp outputs. Use Value: Provides robust, high-current sinking capability to drive incandescent or high-brightness LEDs directly, improving reliability over marginal GPIO-driven solutions. |
| Electromechanical Relay Boards | Fixed-Function Industrial Controllers |
Use Scenario: Selecting one of ten relay coils in sequence-based automation systems using rotary encoder or thumbwheel switch BCD inputs. IC Role / Device Role / Timing Role: Decoding mechanical switch BCD output to activate individual relay drivers, with open-collector outputs interfacing to ULN2003 or similar Darlington arrays. Use Value: Ensures deterministic coil activation without ghosting or crosstalk due to invalid input codes being suppressed (outputs float for 10–15). | Use Scenario: Implementing fixed-state machine logic in PLC I/O modules where BCD-encoded sensor data triggers discrete output actions. IC Role / Device Role / Timing Role: Standalone decoder providing deterministic, low-latency mapping from BCD input bus to ten independent control lines for valve, solenoid, or alarm activation. Use Value: Delivers predictable timing (35 ns) and noise-immune TTL input thresholds, critical for deterministic response in hardwired safety interlocks. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar BCD-to-decimal decoder applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS42N | Same 74LS family, identical pinout and BCD decoding function, but includes internal input clamping diodes and slightly tighter propagation delay (30 ns max). | Valid for same LED/display and relay-board roles; preferred where tighter timing margin or enhanced ESD input protection is required. | Select SN74LS42N if system-level ESD immunity or sub-35 ns timing is critical; otherwise SN74LS145N remains fully interchangeable in legacy designs. |
| 74HC42N | CMOS version with wider supply range (2 V–6 V), lower power, but 5 V-only compatible input thresholds and 17 ns propagation delay; not pin-compatible (different pin assignment for VCC/GND). | Suitable only in new 5 V CMOS designs with redesigned layout; cannot drop-in replace SN74LS145N due to incompatible pinout and drive strength mismatch. | Choose 74HC42N only for new low-power 5 V systems with full layout redesign; avoid for repair or drop-in replacement of SN74LS145N. |
Compared with SN74LS42N, SN74LS145N offers identical functionality and pinout but lacks input clamping diodes, making it slightly more susceptible to input transients; compared with 74HC42N, SN74LS145N provides guaranteed 40 mA sink drive and proven reliability in legacy 5 V TTL systems, despite higher quiescent current.
Availability
SN74LS145N is available at Aetrix Electronics and suitable for industrial panel meters, legacy test equipment displays, and fixed-function controller designs requiring stable component supply across long-lifecycle programs.
Supply support for SN74LS145N 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 ICs with broad industrial, automotive, and aerospace qualification programs.
The SN74LS145N belongs to TI's legacy 74LS logic product line, designed specifically for reliable, low-cost BCD decoding in commercial-grade digital systems where TTL compatibility and direct LED drive are essential.
FAQ
What is the maximum sink current per output of the SN74LS145N?
The SN74LS145N guarantees a minimum output sink current of 40 mA per active-low output (Y0–Y9) under specified VCC and temperature conditions. This rating allows direct driving of standard LEDs with appropriate current-limiting resistors or interfacing to relay driver ICs like the ULN2003. Exceeding this current risks output transistor degradation or thermal shutdown in sustained operation.
Does the SN74LS145N support invalid BCD code suppression?
Yes, the SN74LS145N disables all outputs (Y0–Y9 go high-impedance) when the BCD input code is outside the valid range of 0000–1001 (decimal 0–9). Inputs 1010 through 1111 (decimal 10–15) result in no active output, preventing erroneous activation in systems with incomplete or misaligned BCD data - a key reliability feature in industrial control interfaces.
Can the SN74LS145N be used with a 3.3 V microcontroller?
No, the SN74LS145N is not compatible with 3.3 V logic systems. Its inputs require LS-TTL voltage thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V), but its VCC must be 4.75–5.25 V. A 3.3 V microcontroller GPIO cannot reliably drive SN74LS145N inputs without level-shifting circuitry, and connecting SN74LS145N outputs to 3.3 V inputs risks overvoltage damage unless open-collector pull-up resistors are configured to 3.3 V.
What is the propagation delay of the SN74LS145N and how does it affect timing?
The SN74LS145N has a maximum propagation delay of 35 ns (tPLH and tPHL) under standard load and supply conditions. This delay determines the minimum time between stable BCD input and valid output assertion, enabling reliable operation in synchronous systems clocked up to approximately 10 MHz when cascaded with other 74LS devices. Timing-critical designs must account for this delay in setup/hold budgets.
Is the SN74LS145N RoHS compliant?
Yes, the SN74LS145N is RoHS compliant, as confirmed by Texas Instruments' packaging documentation. It features NiPdAu (NIPDAU) lead finish and meets EU Directive 2011/65/EU requirements. The "Yes" RoHS flag applies to all active orderable variants including SN74LS145N, SN74LS145N.A, and SN74LS145NE4 - verified in TI's official packaging addendum dated 15-Jul-2026.
SN74LS145N Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 16-DIP (0.300", 7.62mm)
- Packaging:
- Bulk
- Product Status:
- Active
- Type:
- Decoder
- Circuit:
- 1 x 4:10
- Independent Circuits:
- 1
- Current - Output High, Low:
- -, 80mA
- Voltage Supply Source:
- Single Supply
- Voltage - Supply:
- 4.75V ~ 5.25V
- Operating Temperature:
- 0°C ~ 70°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 16-PDIP
SN74LS145N FAQ
1.How can I place an order for SN74LS145N through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS145N 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 SN74LS145N reliable?
The price and inventory of SN74LS145N are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS145N is usually 5 days.
3.What payment methods are accepted for SN74LS145N?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS145N transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS145N?
SN74LS145N orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS145N 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 SN74LS145N?
For technical support, including SN74LS145N datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS145N requirements.
6.How does Aetrix verify that SN74LS145N is sourced from the original manufacturer or authorized distributors?
All SN74LS145N 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 SN74LS145N meets industry standards.
7.What is the process for return or replacement of SN74LS145N?
All SN74LS145N units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS145N, 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 SN74LS145N part is unused and in its original packaging.
Return procedure for SN74LS145N:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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