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SN74ALS642AN
Texas Instruments
BUS TRANSCEIVER, ALS SERIES
3348 Pcs New Original In Stock
Element Bit per Element Output
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*Quantity
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Minimum 1
5.0 / 5.0
- (104 Ratings)
SN74ALS642AN
Product Overview
9200146
DiGi Electronics Part Number
SN74ALS642AN-DGManufacturer
Texas Instruments
SN74ALS642AN
Description
BUS TRANSCEIVER, ALS SERIESInventory
3348 Pcs New Original In Stock
Element Bit per Element Output
Quantity
Minimum 1
Minimum 1
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Warranty & Returns
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SN74ALS642AN Technical Specifications
Category
Logic, Buffers, Drivers, Receivers, Transceivers
Packaging
Bulk
Series
*
Product Status
Active
Base Product Number
74ALS642
Datasheet & Documents
HTML Datasheet
SN74ALS642AN-DG
Environmental & Export Classification
RoHS Status
RoHS non-compliant
Moisture Sensitivity Level (MSL)
3 (168 Hours)
REACH Status
REACH Affected
ECCN
EAR99
HTSUS
8542.39.0001
Additional Information
Other Names
TEXTISSN74ALS642AN
2156-SN74ALS642AN
Standard Package
133
Reviews
5.0/5.0-(Show up to 5 Ratings)
Dec 02, 2025
포장 패키지가 견고해서 제품이 전혀 손상되지 않았어요. 배송도 정시에 이루어져서 추천합니다.
Dec 02, 2025
快速且可靠的送貨服務，包裝安全，讓我很滿意這次購物。
Dec 02, 2025
The variety they provide helps in creating tailored solutions for different applications.
Dec 02, 2025
I am thoroughly satisfied with how quickly my order was processed and delivered.
Dec 02, 2025
Received my order within a record time, and the package was intact thanks to careful packing.
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Frequently Asked Questions (FAQ)
What are the critical design considerations when replacing SN74ALS642AN with a modern 3.3V bus transceiver in a legacy 5V TTL system?
When replacing SN74ALS642AN with a lower-voltage alternative like the SN74LVC642A, ensure level-shifting compatibility between 3.3V outputs and 5V inputs. The SN74ALS642AN operates at 5V VCC and has TTL-compatible input thresholds (V_IH ≥ 2V), whereas 3.3V LVC devices may not reliably drive 5V TTL inputs without pull-ups or level translators. Use a bidirectional voltage translator (e.g., TXB0108) if signal direction changes dynamically, or verify that the replacement’s V_OH meets the legacy system’s V_IH requirement—typically requiring ≥2.4V at 4mA load. Failing to address this can cause logic errors or marginal noise margins in high-speed backplane applications.
Can the SN74ALS642AN be safely used in a mixed-voltage system where some nodes operate at 3.3V and others at 5V without damage?
No, the SN74ALS642AN is not 3.3V-tolerant on its inputs when powered at 5V. Applying 3.3V logic signals directly to its inputs may cause excessive current through the input protection diodes if the input voltage exceeds VCC + 0.5V. While 3.3V is below this threshold when VCC = 5V, marginal power sequencing or transient overshoot could risk latch-up or long-term reliability degradation. For safe mixed-voltage operation, use a level-shifting buffer or ensure all inputs are driven from 5V-compatible sources. Consider alternatives like the SN74AVC642A for true voltage-agnostic interfacing.
How does the SN74ALS642AN compare to the SN74HC642N in terms of speed, power, and noise immunity for industrial control backplanes?
The SN74ALS642AN offers faster propagation delay (~7.5 ns typical) and better noise immunity due to its TTL input thresholds (V_IH = 2V, V_IL = 0.8V), making it more robust in electrically noisy industrial environments compared to the SN74HC642N, which uses CMOS thresholds (≈0.7×VCC and ≈0.3×VCC). However, the HC version consumes significantly less static power and supports full rail-to-rail output swing. In high-density backplanes where ground bounce and crosstalk are concerns, the ALS family’s controlled edge rates and stronger output drive (24mA I_OH/I_OL) provide better signal integrity—but at the cost of higher dynamic power. Choose SN74ALS642AN when signal integrity outweighs power efficiency.
What are the reliability risks of using SN74ALS642AN in high-humidity environments given its MSL-3 rating and non-RoHS status?
The SN74ALS642AN’s MSL-3 (168-hour floor life) indicates moderate moisture sensitivity, requiring dry storage and baking if exposed to ambient humidity >30% RH for extended periods before reflow. In high-humidity operating environments, the non-RoHS construction (likely containing leaded solder and older encapsulants) may increase susceptibility to conductive anodic filament (CAF) formation or corrosion over time, especially under bias. Mitigate risk by conformal coating the PCB, maintaining environmental controls (<60% RH), and avoiding continuous high-voltage stress on unused pins. For harsh environments, consider hermetically sealed or newer RoHS-compliant alternatives like the SN74AUP642A, despite requiring level translation.
Is it safe to parallel multiple SN74ALS642AN outputs to increase drive strength in a high-capacitance bus application?
Paralleling SN74ALS642AN outputs is not recommended due to potential current hogging and thermal imbalance. Although each output can source/sink 24mA, slight variations in output voltage thresholds between devices can cause one driver to carry disproportionate current, leading to localized heating and premature failure. Additionally, the ALS series lacks built-in current limiting or thermal shutdown. Instead, use a single higher-drive buffer (e.g., SN74ABT642A with 64mA output) or distribute load across separate enable-controlled channels. If paralleling is unavoidable, add small series resistors (10–22Ω) per output to balance current and reduce ringing—but validate stability with worst-case capacitive loading and temperature rise simulations.
Quality Assurance (QC)
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SN74ALS642AN CAD Models
Texas Instruments SN74ALS642AN PCB symbols & footprints
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