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HomeProductsIntegrated Circuits (ICs)Logic - Buffers, Drivers, Receivers, TransceiversMC74AC240MEL
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MC74AC240MEL - onsemi

Manufacturer Part Number
MC74AC240MEL
Manufacturer
onsemi
Allelco Part Number
32D-MC74AC240MEL
Warranty
1 Year Allelco Warranty - Find out more
Stock Status:
11,200 pcs available, New & Original
Parts Description
IC BUFFER INVERT 6V SOEIAJ-20
Package
SOEIAJ-20
Data sheet
MC74AC240MEL.pdf

Datasheets

MC74AC(T)240.pdf

HTML Datasheet

MC74AC(T)240.pdf

Environmental Information

onsemi REACH.pdf onsemi RoHS.pdf
RoHs Status
 
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Specifications

MC74AC240MEL Tech Specifications
onsemi - MC74AC240MEL technical specifications, attributes, parameters and parts with similar specifications to onsemi - MC74AC240MEL

Product Attribute Attribute Value
Manufacturer onsemi
Voltage - Supply 2V ~ 6V
Supplier Device Package SOEIAJ-20
Series 74AC
Package / Case 20-SOIC (0.209", 5.30mm Width)
Package Tape & Reel (TR)
Output Type 3-State
Operating Temperature -40°C ~ 85°C (TA)
Product Attribute Attribute Value
Number of Elements 2
Number of Bits per Element 4
Mounting Type Surface Mount
Logic Type Buffer, Inverting
Input Type -
Current - Output High, Low 24mA, 24mA
Base Product Number 74AC240

Environmental & Export Classifications

ATTRIBUTE DESCRIPTION
RoHs Status RoHS non-compliant
Moisture Sensitivity Level (MSL) 3 (168 Hours)
REACH Status REACH Unaffected
ECCN EAR99
HTSUS 8542.39.0001

Parts Introduction

MC74AC240MEL Image
MC74AC240MEL (1)

Manufacturer Part Number

MC74AC240MEL

Manufacturer

onsemi

Introduction

The MC74AC240MEL is a high-performance, low-power, 4-bit buffer/line driver with 3-state outputs. It is designed to provide high-current drive capability and is suitable for driving transmission lines, backplane buses, and other capacitive loads.

Product Features and Performance

Quad 3-state noninverting buffer/line driver

24mA sink/source capability per output

Power supply range of 2V to 6V

High-speed operation with typical propagation delay of 5ns

Low power consumption with typical ICC of 2mA

Inputs are TTL/CMOS compatible

Outputs can be connected directly to buses

Product Advantages

High-drive capability for driving capacitive loads

Low power consumption

High-speed operation

TTL/CMOS compatible inputs

Key Reasons to Choose This Product

Reliable and high-performance buffer/line driver solution

Supports a wide range of power supply voltages

Ideal for driving transmission lines, backplane buses, and other capacitive loads

Excellent choice for high-speed digital systems

Quality and Safety Features

Manufactured using advanced CMOS technology for reliable performance

Meets industry-standard safety and regulatory requirements

Compatibility

Compatible with TTL and CMOS logic families

Application Areas

Suitable for use in a wide range of digital systems, including computer peripherals, industrial control equipment, and telecommunications equipment

Product Lifecycle

The MC74AC240MEL is an obsolete product. Alternative products that may be suitable include the MC74VHC240 and MC74LVT240 series. Customers are advised to contact our website's sales team for more information on available options.

Frequently Asked Questions(FAQ)

How does the MC74AC240MEL handle signal integrity in high-noise environments compared to other 74AC240 variants, and what design considerations are critical for reliable operation?
The MC74AC240MEL features 3-state outputs with ±24mA drive capability across a 2V to 6V supply range, enabling robust noise margin management in noisy industrial or automotive environments. Its 74AC logic family provides faster propagation delays than older HC or HCT families, reducing susceptibility to glitches during switching transitions. When comparing to substitutes like the SN74AC240DBR, the MC74AC240MEL’s SOEIAJ-20 packaging offers slightly improved thermal dissipation due to larger exposed pad geometry, which can enhance stability under sustained high-load conditions. However, because it is RoHS non-compliant, designers must evaluate regulatory constraints when substituting. Proper decoupling capacitance (typically 0.1µF ceramic near VCC) and controlled trace impedance on PCBs are essential to maintain signal fidelity, especially at clock frequencies above 50 MHz.
What are the key differences between the MC74AC240MEL and CD74AC240M in terms of pinout, thermal performance, and suitability for space-constrained applications?
The MC74AC240MEL uses the SOEIAJ-20 package, which has a wider body (5.30mm) and includes an exposed thermal pad for better heat dissipation compared to the standard SOIC version of the CD74AC240M. This makes the MC74AC240MEL more suitable for continuous high-current output scenarios. Pin-to-pin compatibility exists between both packages, but layout adjustments may be required due to differing lead pitches and pad configurations. While both support identical voltage ranges and logic functions, the MC74AC240MEL’s enhanced thermal characteristics make it preferable in compact systems where localized heating could otherwise degrade performance. Designers should verify mechanical clearances and solder joint reliability when migrating from CD74AC240M designs.
At what operating frequency does the propagation delay of the MC74AC240MEL begin to impact system timing margins, and how should this be factored into bus interface design?
With typical tPLH/tPHL values around 3.2 ns at 5V and 55°C, the MC74AC240MEL starts affecting timing budgets significantly beyond 80–100 MHz in synchronous systems. In a 4-bit bidirectional buffer application driving multiple loads, cumulative skew from propagation delay variations can exceed setup/hold windows if not accounted for. For example, in a 16-bit data path using two MC74AC240MEL chips, worst-case delay spread could reach 6.4 ns. Engineers should use simulation tools to model end-to-end latency and incorporate guard bands in clock-to-output timing allocations. Additionally, minimizing capacitive loading on outputs—by limiting fan-out or inserting series resistors—can help preserve edge rates and reduce timing uncertainty.
Can the MC74AC240MEL safely drive long PCB traces without additional buffering, and under what conditions might signal degradation occur?
Yes, but only within practical limits. The MC74AC240MEL’s 24mA output current allows driving traces up to approximately 15 cm at 50 pF load before significant rise time degradation occurs. Beyond this, impedance mismatches, crosstalk, and attenuation become problematic, particularly in multi-drop configurations. At 6V supply, output high voltage remains above 4.9V even under full load, preserving logic levels, but output low voltage may rise toward 0.4V due to IR drop, potentially violating VIH thresholds downstream. For traces longer than 10 cm or in parallel bussing scenarios, external line drivers or repeaters should be considered. Termination resistors may also be necessary to prevent reflections, especially in clock distribution networks.
How does the Moisture Sensitivity Level (MSL) rating of MSL 3 affect storage and assembly handling requirements for the MC74AC240MEL?
As an MSL 3 component (168-hour floor life), the MC74AC240MEL must be stored in dry ambient conditions (<60% RH) and consumed within 168 hours after desiccant packaging is opened unless re-bagged with fresh desiccant. This impacts just-in-time inventory practices and increases risk of popcorning during reflow soldering if mishandled. Manufacturers typically enforce this through controlled warehouse humidity and automated packaging systems. Designers sourcing components directly should implement rigorous ESD-safe handling procedures and document traceability to ensure compliance. Failure to adhere to these guidelines can compromise solder joint integrity and lead to latent failures post-deployment.
Is the MC74AC240MEL compatible with 5V-tolerant inputs from 3.3V logic devices, and what precautions apply when interfacing across voltage domains?
Yes, the MC74AC240MEL accepts inputs down to 0V even when powered at 5V, making it compatible with 3.3V logic families such as LVTTL or LVC. However, when the MC74AC240MEL operates at 2.5V, input high threshold rises to ~1.8V, so direct connection to 3.3V outputs requires ensuring that 3.3V logic swings fully meet this requirement. In mixed-voltage systems, level translation is generally safe due to the AC family’s wide input hysteresis. Still, designers should avoid back-driving the device by connecting unpowered inputs to active signals, as this can cause latch-up or excessive current draw. Using Schottky clamps or pull-down resistors helps mitigate such risks.
What environmental and regulatory limitations should be considered when selecting the MC74AC240MEL over alternative 74AC240 implementations?
The MC74AC240MEL is RoHS non-compliant, meaning it contains lead-based finishes or other restricted substances banned under EU Directive 2011/65/EU. This restricts its use in consumer electronics, medical devices, or any product destined for European markets without exemption. Additionally, while the device operates reliably from -40°C to +85°C, prolonged exposure to corrosive atmospheres or high-humidity environments may accelerate package degradation due to lack of conformal coating options. In contrast, modern substitutes like the SN74AC240NSR offer RoHS compliance and similar performance. Designers must weigh functional equivalence against certification requirements early in the specification phase.
How do input leakage currents and power consumption compare between the MC74AC240MEL and newer CMOS alternatives like the 74LVC240, particularly in battery-powered applications?
The MC74AC240MEL draws static power primarily due to internal biasing structures, resulting in quiescent ICC of ~20 µA per gate at 5V and 25°C. While still low, this exceeds the sub-1 µA typical of 74LVC240 devices, which use advanced CMOS processes with lower subthreshold leakage. In a system requiring 16 buffered lines active continuously, the MC74AC240MEL would consume ~640 µA versus ~16 µA for an equivalent LVC implementation—a factor of 40 difference. For portable or energy-sensitive designs, substituting the MC74AC240MEL with a 74LVC240 variant could significantly extend battery life. However, speed trade-offs (~10 ns slower propagation) and package compatibility must also be evaluated.
What happens to output enable functionality if the OE pins of the MC74AC240MEL are left floating during operation?
Floating OE pins create undefined states that can lead to unintended output activation, causing bus contention or excessive power dissipation. Although the 74AC family exhibits relatively high input impedance, stray capacitance and noise coupling can induce transient logic levels. Best practice dictates tying unused OE inputs directly to VCC (for active-low enable) or GND (for active-high, though MC74AC240MEL uses active-low OE). Leaving them floating violates recommended operating conditions and increases susceptibility to EMI-induced glitches. This risk is amplified in high-impedance transmission lines or long interconnects common in distributed I/O architectures.
Can the MC74AC240MEL be used in hot-swap applications where live insertion into powered backplanes is required?
Not without external protection. Hot-swap events generate inductive kick and inrush current that can exceed the MC74AC240MEL’s absolute maximum ratings momentarily. Without slew-rate control or pre-charge circuits, simultaneous assertion of multiple outputs during insertion may cause internal parasitic thyristor structures to trigger latch-up, especially if supply sequencing isn’t strictly managed. While the device itself doesn’t include built-in hot-swap immunity, adding series current-limiting resistors (e.g., 10Ω) and TVS diodes on outputs can mitigate damage. Alternatively, using dedicated hot-swap controllers upstream ensures gradual enablement and protects both the MC74AC240MEL and connected loads.
How does package parasitics affect switching behavior in the MC74AC240MEL when driving capacitive loads above 100 pF?
The SOEIAJ-20 package introduces higher inductance and resistance compared to smaller SOT-23 implementations, increasing turn-on delay and ringing on large capacitive loads. At 100 pF, rise times may extend beyond 20 ns, approaching the device’s propagation delay budget. This can distort signal edges and increase electromagnetic emissions. To minimize effects, keep output traces short and use low-ESR capacitors for decoupling. If driving >200 pF loads routinely, consider adding source termination or using buffer chains with intermediate isolation. Simulation with IBIS models helps predict real-world performance before prototyping.
Are there timing derating considerations for the MC74AC240MEL when operated near the extremes of its supply voltage or temperature range?
Yes. Propagation delay increases by roughly 15–20% when operating at 2.0V versus 5.0V, and further degrades at elevated temperatures due to reduced carrier mobility. For instance, at 2.0V and 85°C, tPHL might rise to ~4.1 ns, narrowing timing margins in tight-loop feedback systems. Similarly, at -40°C, slight parameter shifts occur but remain within datasheet guarantees. Designers should apply safety factors in critical paths—such as memory interfaces or synchronous buses—accounting for worst-case combinations of VCC = 2.0V and TA = 85°C. Monte Carlo analysis during FPGA co-design phases is advisable for high-reliability applications.
What substitution risks exist when replacing the MC74AC240MEL with SN74AC240DBR in existing PCB layouts, and how can they be mitigated?
The SN74AC240DBR uses a standard SOIC-20 package with 150-mil width, whereas the MC74AC240MEL employs a 20-SOIC variant with 5.30mm width—often referred to as “wide-body SOIC.” While pinouts are identical, footprint mismatch prevents direct replacement without redesign. Additionally, the SN74AC240DBR lacks the exposed thermal pad, reducing thermal conductivity by ~30%. If original design relied on passive cooling via copper pour, junction temperatures could rise by 10–15°C under sustained loads. Mitigation involves updating Gerber files, verifying clearance with adjacent components, and possibly enhancing PCB heatsinking if output currents exceed 15mA per channel.
How does the 3-state output architecture of the MC74AC240MEL impact bus contention scenarios in multi-master systems?
The tri-state feature allows multiple devices to share a common bus by enabling only one driver at a time. However, improper enable sequencing can still result in overlapping active states if OE signals aren’t synchronized. In worst-case scenarios, two MC74AC240MEL chips asserting conflicting logic levels simultaneously could produce shoot-through currents up to 48 mA (sum of both outputs), stressing bond wires and potentially damaging outputs. To prevent this, implement strict arbitration logic or use open-drain configurations with pull-ups. Monitoring OE assertion timing relative to data changes minimizes risk in microcontroller-driven bus architectures.
What role does input capacitance play in determining maximum fan-out for the MC74AC240MEL, and how does this compare to older TTL buffers?
Each input of the MC74AC240MEL presents ~2–3 pF of input capacitance. Driving N loads adds N × Cload to this value, affecting rise/fall times and loading on preceding stages. For example, driving eight 74HC04 gates (each with 5 pF input capacitance) results in 42 pF total load, extending rise time to ~15 ns—well within acceptable limits. Compared to classic 74LS240 buffers with higher input impedance but slower speeds, the MC74AC240MEL supports greater effective fan-out due to stronger drive strength. Still, exceeding 10 driven loads may necessitate staging with additional buffering to maintain signal integrity.
Why might a designer choose the MC74AC240MEL despite its RoHS non-compliance when cost and availability outweigh regulatory concerns?
In legacy industrial equipment or military/aerospace subsystems where obsolescence is a concern, sourcing stable inventory from authorized distributors may justify using non-RoHS parts. The MC74AC240MEL benefits from mature manufacturing processes, extensive qualification history, and broad distributor stock—unlike newer alternatives still ramping up production. Furthermore, its 24mA output current and 6V tolerance provide robustness unmatched by most modern low-voltage CMOS buffers. If the end product avoids regulated regions and prioritizes lifecycle continuity over compliance, the MC74AC240MEL remains a viable choice pending planned migration to compliant substitutes in next-gen revisions.

Parts with Similar Specifications

The three parts on the right have similar specifications to onsemi MC74AC240MEL

Product Attribute MC74AC240MELG MC74AC241MEL MC74AC240ML1 MC74AC240M
Part Number MC74AC240MELG MC74AC241MEL MC74AC240ML1 MC74AC240M
Manufacturer onsemi onsemi onsemi onsemi
Voltage - Supply - - - -
Operating Temperature - -40°C ~ 85°C 0°C ~ 70°C -40°C ~ 85°C
Logic Type - - - -
Number of Elements - - - -
Current - Output High, Low - - - -
Number of Bits per Element - - - -
Package / Case - 196-LFBGA 16-DIP (0.300', 7.62mm) 64-VFQFN Exposed Pad
Mounting Type - Surface Mount Through Hole Surface Mount
Package - Tape & Reel (TR) Tube Tape & Reel (TR)
Series - - - -
Base Product Number - DAC34H84 MAX500 ADS62P42
Supplier Device Package - 196-NFBGA (12x12) 16-PDIP 64-VQFN (9x9)
Input Type - - - Differential
Output Type - Current - Unbuffered Voltage - Buffered -

MC74AC240MEL Datasheet PDF

Download MC74AC240MEL pdf datasheets and onsemi documentation for MC74AC240MEL - onsemi.

Datasheets
MC74AC(T)240.pdf
HTML Datasheet
MC74AC(T)240.pdf
Environmental Information
onsemi REACH.pdf onsemi RoHS.pdf

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MC74AC240MEL Image

MC74AC240MEL

onsemi
32D-MC74AC240MEL

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