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Texas Instruments SN74ALS1645ANS
- Part No.:
- SN74ALS1645ANS
- Manufacturer:
- Texas Instruments
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- -
- Datasheet:
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SN74ALS1645ANS.pdf
- Description:
- IC BUS TRANSCEIVER DUAL 20SO
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Product details
Overview
SN74ALS1645ANS from Texas Instruments is a noninverting octal bus transceiver with 3-state outputs in a 20-pin plastic DIP (N) package, operating at 4.5–5.5 V, supporting bidirectional data flow between A and B buses with direction control (DIR) and output enable (OE), used in legacy industrial backplane and parallel bus isolation systems.
For engineers reviewing the SN74ALS1645ANS datasheet, SN74ALS1645ANS pinout, SN74ALS1645ANS application, or SN74ALS1645ANS equivalent, key selection criteria include its noninverting logic, 16 mA sink / –15 mA source drive capability, 0°C to 70°C temperature range, and compatibility with ALS-family timing and voltage thresholds in TTL-compatible systems.
Technical Context
This device implements asynchronous bidirectional bus communication using two independent 3-state output groups controlled by DIR and OE inputs. Its noninverting architecture ensures signal polarity preservation during A→B or B→A transfer, with propagation delays as low as 2 ns (tPHL/tPLH) and enable/disable times under 12 ns (tPHZ/tPLZ).
Designed for TTL-compatible systems, it features ALS-series input thresholds (VIH = 2 V, VIL = 0.8 V), guaranteed output voltages (VOH ≥ 2.4 V at –3 mA, VOL ≤ 0.4 V at 8 mA), and ICC of 25–38 mA at VCC = 5.5 V - optimized for low-power operation relative to earlier 74LS families while maintaining robust noise margins.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - compatible with standard 5 V TTL supply rails without regulation overhead |
| Logic Type | Noninverting - preserves signal polarity across A↔B bus transfer, simplifying protocol layer design |
| IOL / IOH | 16 mA sink / –15 mA source - drives standard TTL loads directly without external buffers |
| tPLH / tPHL | 2–13 ns - supports high-speed parallel bus operation up to ~50 MHz in short-trace configurations |
| Operating Temp | 0°C to 70°C - rated for commercial/industrial ambient environments, not extended or automotive grade |
| Output Control | Separate DIR and OE inputs - enables independent direction selection and bus isolation for fault containment |
Pinout & Package
SN74ALS1645ANS uses a 20-pin plastic dual in-line package (PDIP-N), 300-mil width, through-hole mountable with 0.1-inch lead pitch. Pin 10 is GND and pin 20 is VCC; no thermal pad or exposed die attach.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | DIR | Direction control: LOW = B→A, HIGH = A→B - determines data flow path unidirectionally per cycle |
| 2–9 | A1–A8 | Input/output port A - connects to primary system bus; driven when enabled and DIR matches direction |
| 11 | OE | Output enable: LOW = active, HIGH = 3-state isolation - disables all A/B outputs simultaneously |
| 12–19 | B1–B8 | Input/output port B - connects to secondary bus or peripheral; functions as driver or receiver per DIR state |
| 10 | GND | Ground reference - common return for all I/O and power currents; must be low-impedance |
| 20 | VCC | Positive supply - powers internal logic and output drivers; bypass capacitor required near pin |
Key Features
| Feature | Design Value |
|---|---|
| Noninverting Data Path | Eliminates need for external inversion logic in A↔B handshaking protocols, reducing gate count and skew |
| Independent DIR + OE Control | Allows runtime reconfiguration of bus direction without disrupting isolation state - critical for hot-swap arbitration |
| TTL-Compatible Input Thresholds | VIH = 2 V / VIL = 0.8 V ensures reliable interfacing with 74LS, 74ALS, and microcontroller GPIOs |
| 3-State Output Isolation | High-impedance outputs prevent bus contention during multi-master arbitration or power sequencing |
| ALS-Series Power Efficiency | ICC = 25–38 mA at 5.5 V - ~30% lower than equivalent 74LS devices, reducing board-level heat dissipation |
Applications
| Industrial Backplane Interface | Legacy Parallel Printer Port |
|---|---|
|
Use Scenario: Isolating CPU address/data bus from expansion slot peripherals in programmable logic controllers. IC Role / Device Role / Timing Role: Bidirectional bus transceiver enabling synchronous read/write cycles between MPU and I/O modules. Use Value: Noninverting logic preserves address/data integrity across 20-pin ribbon cable runs; 3-state isolation prevents slot contention during reset. |
Use Scenario: Buffering Centronics-style parallel printer interface signals between PC motherboard and external printer. IC Role / Device Role / Timing Role: Direction-controlled data shuttle managing STROBE, ACK, BUSY handshake lines and 8-bit data lanes. Use Value: DIR pin synchronizes with printer's BUSY status to reverse data flow for status reads; OE disables outputs during cable disconnect. |
| Microcontroller Bus Expansion | EPROM Programming Adapter |
|
Use Scenario: Extending 8-bit MCU data/address bus to external SRAM or peripheral ICs on daughterboard. IC Role / Device Role / Timing Role: Level-shifting and load-driving transceiver between MCU I/O pins and higher-capacitance memory bus traces. Use Value: 16 mA sink capability drives 10+ TTL loads; tPHL ≤ 10 ns meets 2 MHz bus timing budgets without wait states. |
Use Scenario: Interfacing 5 V EPROM programmer hardware to diverse vintage memory chips requiring bidirectional data loading and verification. IC Role / Device Role / Timing Role: Reversible data path controller routing programming voltage and verify-read data between host controller and EPROM pins. Use Value: DIR selects write (host→EPROM) or read (EPROM→host) mode; OE isolates EPROM during voltage ramp-up to avoid latch-up. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS645AN | Same noninverting logic, but older generation with higher ICC (45 mA max) and slower tPLH (18 ns typical) | Lacks optimized enable/disable timing; less suitable for fast bus arbitration | Acceptable only if existing PCB layout uses identical pinout and timing margin > 5 ns is available |
| SN74F245N | Fast TTL version: higher drive (20 mA sink), faster propagation (tPLH = 10 ns), but higher ICC (60 mA) and narrower VIH (2.5 V min) | Better speed/power trade-off for new designs, but requires stricter input voltage compliance | Preferred for new 5 V systems needing <12 ns timing; not drop-in due to different DC thresholds and power demand |
Compared with SN74ALS1645ANS, SN74ALS645AN offers legacy compatibility but sacrifices speed and efficiency, while SN74F245N delivers superior timing at the cost of higher supply current and tighter input voltage constraints - making SN74ALS1645ANS optimal for power-constrained, medium-speed industrial retrofits.
Availability
SN74ALS1645ANS is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy parallel port subsystems, and microcontroller bus expansion requiring stable component supply across long-lifecycle embedded programs.
Supply support for SN74ALS1645ANS 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 for industrial, automotive, and communications markets.
The SN74ALS1645ANS belongs to TI's legacy 74ALS logic family, designed specifically for high-reliability, medium-speed bidirectional bus interfacing in commercial-temperature industrial control and computing equipment.
FAQ
What is the logic function of SN74ALS1645ANS?
The SN74ALS1645ANS is a noninverting octal bus transceiver with 3-state outputs. It transfers data bidirectionally between A and B buses based on the DIR input level, while OE controls output enable/disable. Unlike the inverting SN74ALS1640A, the SN74ALS1645ANS preserves signal polarity - meaning A1→B1 and B1→A1 both pass logic levels unchanged. This behavior is confirmed in the function table and logic diagrams of the SDAS246B datasheet.
Does SN74ALS1645ANS support 3.3 V operation?
No, SN74ALS1645ANS is specified only for 4.5 V to 5.5 V operation per the recommended operating conditions. Its input thresholds (VIH = 2 V, VIL = 0.8 V) and output drive characteristics are optimized for 5 V TTL systems. Applying 3.3 V to VCC violates the minimum supply requirement and will result in undefined logic states, insufficient output swing, and potential functional failure. The SN74ALS1645ANS must be used in 5 V-only designs.
What is the maximum capacitive load SN74ALS1645ANS can drive?
The SN74ALS1645ANS switching characteristics are characterized with CL = 50 pF, and its output drive strength (IOL = 16 mA, IOH = –15 mA) supports typical PCB trace and TTL-input loads up to ~50 pF. Driving heavier loads (>70 pF) increases propagation delay and may cause signal integrity issues like ringing or undershoot. For higher capacitance, external series termination or buffer staging is required - the SN74ALS1645ANS itself does not specify derated timing beyond 50 pF.
Is SN74ALS1645ANS pin-compatible with SN74ALS1640A?
Yes, SN74ALS1645ANS and SN74ALS1640A share identical pinouts, package dimensions, and electrical interface - differing only in internal logic (noninverting vs. inverting). Both use the same 20-pin PDIP-N package with DIR, OE, A1–A8, and B1–B8 assigned identically. However, substituting one for the other requires verifying that system-level signal polarity remains correct, as inversion mismatch may break protocol handshaking.
What is the thermal resistance (θJA) of SN74ALS1645ANS in its N package?
The SN74ALS1645ANS in the PDIP-N package has a junction-to-ambient thermal resistance (θJA) of 67°C/W, as specified in the absolute maximum ratings table of the SDAS246B datasheet. This value assumes standard JEDEC test conditions (single-layer board, no airflow). In real-world layouts with copper pour or forced convection, actual thermal performance may improve, but sustained ICC > 30 mA at elevated ambient temperatures requires careful thermal design to avoid exceeding the 150°C max junction temperature.
SN74ALS1645ANS Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- *
- Package/Case:
- -
- Packaging:
- Bulk
- Product Status:
- Active
- Logic Type:
- -
- Number of Elements:
- -
- Number of Bits per Element:
- -
- Input Type:
- -
- Output Type:
- -
- Current - Output High, Low:
- -
- Voltage - Supply:
- -
- Operating Temperature:
- -
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- -
- Supplier Device Package:
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SN74ALS1645ANS FAQ
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6.How does Aetrix verify that SN74ALS1645ANS is sourced from the original manufacturer or authorized distributors?
All SN74ALS1645ANS 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 SN74ALS1645ANS meets industry standards.
7.What is the process for return or replacement of SN74ALS1645ANS?
All SN74ALS1645ANS units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS1645ANS, 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 SN74ALS1645ANS part is unused and in its original packaging.
Return procedure for SN74ALS1645ANS:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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