Part A
74HC139D
Toshiba Halbleiter und Speicher
- Lifecycle
- Active
- Stock
- 4290 Stückzahl
- Package
- SOIC-16
- Series
- Logic.Signal Schalter, Multiplexer, Decoder
Replacement verdict
Not a drop-in replacement
The 74HC126D and 74HC139D are not functionally interchangeable. The 74HC126D is a quad bus buffer with 3-state outputs, while the 74HC139D is a dual 2-to-4 line decoder/demultiplexer. Their logic functions, pin configurations, and output characteristics are fundamentally different, making direct substitution impossible without circuit redesign.
Different logic function
Different output type
Different pinout
Different channel count
Parts at a glance
Part B
74HC126D
Toshiba Halbleiter und Speicher
- Lifecycle
- Active
- Stock
- 7257 Stückzahl
- Package
- SOIC-14
- Series
- Logic c Puffer, Treiber, Empfänger, Transceiver
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HC126D | 74HC139D | Why it matters |
|---|---|---|---|
| Logic Function | Quad Buffer with 3-State Outputs | Dual 2-to-4 Line Decoder/Demultiplexer | The core logic function determines whether the parts can substitute for each other; these are fundamentally different functions and are not functionally interchangeable. |
| Number of Channels | 4 | 2 | Channel count affects how many independent signal paths can be handled, impacting circuit design and board layout. |
| Output Type | 3-State | Push-Pull (Active Low) | Output type determines whether outputs can be tied to a shared bus and how they drive connected loads. |
| Control Inputs | Output Enable (active high) per channel | Address inputs (A0, A1) and enable (active low) per decoder | Control input scheme defines how the device is activated and selected within a system. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | Supply voltage range must match the system rail to ensure reliable logic levels and safe operation. |
| Propagation Delay (typical at 5 V) | ~11 ns | ~13 ns | Propagation delay affects timing margins and maximum operating frequency in synchronous designs. |
| Output Drive Current | ±6 mA (at 5 V) | ±4 mA (at 5 V) | Drive current determines the ability to drive loads such as LEDs, other logic inputs, or transmission lines. |
| Package | SOIC-14 | SOIC-16 | Package footprint and pin count must match the PCB layout for physical compatibility. |
| Pin Count | 14 | 16 | Pin count affects board layout and whether the part can be dropped into an existing footprint. |
| Operating Temperature Range | -40 °C to +125 °C | -40 °C to +125 °C | Temperature range ensures the device operates reliably in the target environment. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC139D | 74HC126D |
|---|---|---|
| Series | 74HC | 74HC |
| Part Status | Obsolete | Active |
| Type | Decoder/Demultiplexer | - |
| Circuit | 1 x 2:4 | - |
| Independent Circuits | 2 | - |
| Current - Output High Low | 5.2mA, 5.2mA | 7.8mA, 7.8mA |
| Voltage Supply Source | Single Supply | - |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Operating Temperature | -40°C ~ 85°C | -40°C ~ 125°C (TA) |
| Mounting Type | Surface Mount | Surface Mount |
| Logic Type | - | Buffer, Non-Inverting |
| Number of Elements | - | 4 |
| Number of Bits per Element | - | 1 |
| Output Type | - | 3-State |
Frequently asked questions
What are the primary functions of the 74HC126D and 74HC139D?
The 74HC126D is a quad non-inverting 3-state buffer with active-HIGH output enable pins, used for signal buffering and bus driving. The 74HC139D is a dual 2-to-4 line decoder/demultiplexer with active-LOW outputs, used for address decoding and data routing.
Can the 74HC126D and 74HC139D be used interchangeably in a design?
No. They perform fundamentally different logic functions. The 74HC126D provides buffered 3-state outputs controlled by individual enable pins, while the 74HC139D decodes a 2-bit binary input into one of four mutually exclusive active-LOW outputs. Substitution requires a complete redesign of the surrounding logic.
Do the 74HC126D and 74HC139D share the same package and pinout?
Both devices are commonly offered in a 16-pin SOIC package (the "D" suffix in Nexperia naming denotes SO16). However, their pinouts are not identical because their internal logic and pin functions differ. The 74HC126D uses pins for four buffer inputs, four outputs, and four enable controls, while the 74HC139D uses pins for two sets of 2-bit address inputs, four active-LOW outputs per decoder, and two active-LOW enable inputs.
What are the key electrical characteristics of the 74HC126D?
The 74HC126D operates from a 2.0 V to 6.0 V supply, features 3-state non-inverting outputs, and provides high noise immunity typical of HC-family CMOS logic. It has standard symmetrical output drive and is specified for operation over the -40 °C to +125 °C temperature range in the SO16 package.
What are the key electrical characteristics of the 74HC139D?
The 74HC139D operates from a 2.0 V to 6.0 V supply and contains two independent 2-to-4 decoders. Each decoder has two active-LOW enable inputs (Ea and Eb) and four active-LOW outputs (Y0 to Y3). It is a standard HC-family CMOS device specified over the -40 °C to +125 °C temperature range in the SO16 package.
Are the 74HC126D and 74HC139D compatible with 3.3 V and 5 V logic systems?
Yes. Both devices are specified for a supply voltage range of 2.0 V to 6.0 V, which covers both 3.3 V and 5 V logic levels. Their CMOS inputs and outputs are compatible with standard HC-family logic thresholds when operated at the corresponding supply voltage.
What is the difference in output drive capability between the 74HC126D and 74HC139D?
Both devices are standard HC-family CMOS logic and are specified with symmetrical output drive typical of the 74HC series. The 74HC126D is a buffer intended for driving bus lines and similar loads, while the 74HC139D is a decoder whose outputs are also standard HC-family CMOS outputs. Detailed drive current specifications should be verified from the respective manufacturer datasheets.
Which device is better suited for address decoding in a microprocessor system?
The 74HC139D is the appropriate choice for address decoding because it is a dual 2-to-4 decoder/demultiplexer designed to select one of four outputs based on a 2-bit address. The 74HC126D is a quad 3-state buffer and does not perform decoding; it is used for signal buffering and bus isolation instead.