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Texas Instruments SN74LS245DBR
- Part No.:
- SN74LS245DBR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SSOP (0.209", 5.30mm Width)
- Datasheet:
-
SN74LS245DBR.pdf
- Description:
- IC TXRX NON-INVERT 5.25V 20SSOP
- Quantity:
- Payment:
- Shipping:
Inventory:4,834
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Product details
Overview
SN74LS245DBR from Texas Instruments is an octal bus transceiver with 3-state outputs, designed for asynchronous bidirectional data transfer between A and B buses in TTL-level systems. It features direction control (DIR), active-low output enable (OE), 8 ns typical propagation delay, ±15 mA high-level/24 mA low-level output drive, and hysteresis-enhanced noise immunity on bus inputs - used in industrial backplane interfaces and legacy embedded bus isolation.
For engineers reviewing the SN74LS245DBR datasheet, SN74LS245DBR pinout, SN74LS245DBR application, or SN74LS245DBR equivalent, this page delivers verified electrical specs, SSOP-20 package details, functional mode logic, real-world bus-driving use cases, and two validated alternative parts for legacy system maintenance and redesign.
Technical Context
The SN74LS245DBR implements Schottky transistor logic (TTL) with PNP input structures to reduce DC loading on shared bus lines. Its dual-bus architecture supports bidirectional flow controlled by a single DIR pin, while OE independently places all eight channels into high-impedance state for bus isolation.
It operates within 4.75 V–5.25 V supply range at 0°C–70°C ambient, delivering 24 mA sink and –15 mA source capability per channel. Input hysteresis (0.2–0.4 V) improves noise margins, and propagation delays are tightly specified at 8–12 ns under 45 pF load conditions.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | TTL (Schottky LS), compatible with standard 5-V TTL voltage thresholds and drive levels |
| Supply Voltage | 4.75 V–5.25 V - ensures stable operation across commercial temperature range without rail shift |
| Output Drive | 24 mA sink / –15 mA source - sufficient to drive multiple TTL loads or long ribbon cables |
| Propagation Delay | 8–12 ns (tPLH/tPHL) - enables reliable timing in 20–30 MHz bus systems with light capacitive loading |
| Input Hysteresis | 0.2–0.4 V - increases noise immunity on shared bus lines subject to crosstalk or ground bounce |
| ESD Rating | ±2500 V HBM - meets standard handling requirements for board assembly in non-classified environments |
| Thermal Resistance | RθJA = 91.7 °C/W (SSOP) - requires minimal heatsinking in low-power bus interface applications |
Pinout & Package
SN74LS245DBR uses a 20-pin SSOP (Shrink Small Outline Package) with 0.65 mm lead pitch and 7.20 mm × 5.30 mm body size, optimized for high-density PCB layouts while maintaining hand-solderability.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (DIR) | Direction control input | Low = B→A data flow; High = A→B data flow - determines signal path polarity for all 8 channels |
| 2–9 (A1–A8) | Bidirectional I/O (A side) | Connects to local bus; functions as input or output depending on DIR state and OE status |
| 10 (GND) | Ground reference | Primary return path for logic and output currents; must be low-impedance to minimize ground bounce |
| 11–18 (B8–B1) | Bidirectional I/O (B side) | Connects to remote bus or peripheral; mirrors A-side behavior with reversed pin order |
| 19 (OE) | Active-low output enable | Low = all channels enabled; High = all outputs in high-Z - enables bus arbitration and hot-swap isolation |
| 20 (VCC) | Positive supply | 5 V nominal power rail; requires local 0.1 µF bypass capacitor per device to suppress switching noise |
Key Features
| Feature | Design Value |
|---|---|
| 3-State outputs | Enables true bus contention avoidance - all A/B pins enter high-impedance simultaneously when OE = HIGH |
| PNP input structure | Reduces input current draw to ≤0.1 mA per pin, minimizing loading on upstream drivers like MCUs or FPGAs |
| Hysteresis on A/B inputs | 0.2–0.4 V threshold separation prevents chatter during slow-rising or noisy bus transitions |
| Standard '245 pinout | Ensures drop-in compatibility with legacy designs using SN74LS245 variants in SOIC, PDIP, or SSOP packages |
| Commercial temp range | 0°C to 70°C operation - suitable for office, factory floor, and indoor embedded equipment without extended thermal design |
Applications
| Industrial Backplane Interface | Legacy MCU Bus Extension |
|---|---|
|
Use Scenario: Connecting microcontroller subsystems to a shared 8-bit parallel backplane in programmable logic controllers. IC Role / Device Role / Timing Role: Bidirectional level-shifting and drive-strengthening transceiver isolating CPU bus from field I/O modules. Use Value: Enables 24 mA drive per line to overcome 20+ cm ribbon cable capacitance while maintaining <12 ns skew across all 8 bits. |
Use Scenario: Extending GPIO bus of an aging 8051-based controller to external memory or peripheral ICs. IC Role / Device Role / Timing Role: Octal buffer/transceiver providing direction control and output disable for shared address/data multiplexing. Use Value: Replaces discrete transistor buffers with single-package solution, reducing layout area and interconnect inlays by >60%. |
| Test Equipment Data Bus | Factory Automation I/O Hub |
|
Use Scenario: Interfacing DUT (device under test) signals to automated test equipment via parallel digital bus. IC Role / Device Role / Timing Role: Isolating tester logic from DUT during configuration, then enabling synchronized data capture in burst mode. Use Value: OE-controlled high-Z state prevents back-driving during test setup; DIR toggling supports both stimulus and response phases. |
Use Scenario: Centralized I/O expansion module linking PLC CPU to distributed sensor/actuator nodes over flat cable. IC Role / Device Role / Timing Role: Bus repeater strengthening weak MCU outputs to drive multiple opto-isolators and relay drivers. Use Value: 24 mA sink capability directly drives LED indicators and small-signal relays without external driver stages. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS245N | PDIP-20 package; RθJA = 46.1 °C/W; same electrical specs and pinout | Through-hole mounting; higher thermal dissipation; suited for prototyping and low-volume industrial boards | Select when manual assembly, rework, or legacy footprint compatibility is required |
| SN74LS245DWR | SOIC-20 package; RθJA = 79.0 °C/W; identical logic function and timing | Surface-mount but wider 12.8 mm × 7.5 mm body; better thermal performance than SSOP but larger PCB area | Choose for mixed-technology boards where SOIC is already standardized and space permits |
Compared with SN74LS245N and SN74LS245DWR, the SN74LS245DBR offers the smallest PCB footprint (7.2 mm × 5.3 mm) among production-qualified LS245 variants, making it optimal for space-constrained industrial control modules where thermal load remains below 150 mW.
Availability
SN74LS245DBR is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy MCU bus extensions, test equipment data buses, and factory automation I/O hubs requiring stable component supply across long-lifecycle programs.
Supply support for SN74LS245DBR 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 company founded in 1930, specializing in analog, embedded processing, and logic solutions with broad industrial, automotive, and communications reach.
The SN74LS245DBR belongs to TI's legacy TTL logic portfolio, engineered specifically for robust, low-cost bidirectional bus interfacing in commercial-grade industrial and instrumentation systems.
FAQ
What is the maximum operating temperature for the SN74LS245DBR?
The SN74LS245DBR is rated for operation from 0°C to +70°C ambient temperature. This commercial-grade specification aligns with its SSOP packaging and intended use in indoor industrial electronics, not extended-temperature environments. Exceeding 70°C may cause parameter drift or accelerated aging; thermal derating is not defined in the datasheet.
Does the SN74LS245DBR support 3.3-V logic interfaces?
No, the SN74LS245DBR is a 5-V TTL device with VIH(min) = 2.0 V and VIL(max) = 0.8 V. It is not 3.3-V tolerant: direct connection to 3.3-V CMOS outputs risks marginal high-level recognition, and driving 3.3-V inputs may exceed their absolute maximum ratings. Level-shifting circuitry is required for interoperability.
How does the DIR pin control data flow direction in the SN74LS245DBR?
In the SN74LS245DBR, DIR = HIGH enables A→B data transmission; DIR = LOW enables B→A transmission. This single-pin control synchronously configures all eight channels - no per-channel direction selection is possible. The direction remains fixed until DIR changes, independent of OE state.
Can unused channels of the SN74LS245DBR be left floating?
No. Unused A/B channel pins must be terminated to the same logic level on both sides (e.g., tie A4 and B4 to GND or VCC together) to prevent floating inputs from causing excessive current draw or oscillation. Leaving them unconnected violates TI's layout guidelines and risks increased power consumption or erratic behavior.
What is the purpose of the hysteresis on SN74LS245DBR bus inputs?
The hysteresis (0.2–0.4 V) on SN74LS245DBR A/B inputs widens the voltage gap between rising and falling input thresholds, preventing multiple transitions during slow or noisy signal edges - critical for reliable operation on shared, unterminated, or long ribbon-cable buses prone to ringing and crosstalk.
SN74LS245DBR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 20-SSOP (0.209", 5.30mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Logic Type:
- Transceiver, Non-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-SSOP
SN74LS245DBR FAQ
1.How can I place an order for SN74LS245DBR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS245DBR 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 SN74LS245DBR reliable?
The price and inventory of SN74LS245DBR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS245DBR is usually 5 days.
3.What payment methods are accepted for SN74LS245DBR?
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4.How is shipping managed for SN74LS245DBR?
SN74LS245DBR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS245DBR 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 SN74LS245DBR?
For technical support, including SN74LS245DBR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS245DBR requirements.
6.How does Aetrix verify that SN74LS245DBR is sourced from the original manufacturer or authorized distributors?
All SN74LS245DBR 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 SN74LS245DBR meets industry standards.
7.What is the process for return or replacement of SN74LS245DBR?
All SN74LS245DBR units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS245DBR, 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 SN74LS245DBR part is unused and in its original packaging.
Return procedure for SN74LS245DBR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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