Part A
74HC139D
Toshiba Semiconductor and Storage
- Lifecycle
- Active
- Stock
- 4290 PCS
- Package
- SOIC-16
- Series
- Lógica - Conmutadores de sinais, Multiplexers, Decodificadores
Replacement verdict
Not a drop-in replacement
The 74HC125D and 74HC139D are not functionally interchangeable despite sharing the same 74HC logic family and SOIC-14 package. The 74HC125D provides four independent non-inverting tri-state buffers with active-low output enable, while the 74HC139D is a dual 2-to-4 line decoder/demultiplexer with active-low enable inputs. Their internal logic functions, pin assignments, and signal flow are fundamentally different, so substituting one for the other is not possible without a complete circuit redesign.
Different logic function
Different pinout
Different input/output configuration
Different enable scheme
Parts at a glance
Part B
74HC125D
Toshiba Semiconductor and Storage
- Lifecycle
- Active
- Stock
- 3803 PCS
- Package
- SOIC-14
- Series
- Lógica - Buffers, Drivers, Receivers, Transceivers
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HC125D | 74HC139D | Why it matters |
|---|---|---|---|
| Logic Function | Quad Buffer/Line Driver with 3-state outputs | Dual 2-to-4 Line Decoder/Demultiplexer | The core logic function determines whether the devices are functionally interchangeable; these are fundamentally different functions and cannot substitute for each other. |
| Number of Channels | 4 | 2 decoders (each 2-to-4) | Channel count affects how many independent signals can be handled, impacting circuit design and board layout. |
| Output Type | 3-state (tri-state) | Active LOW outputs | Output type determines bus-sharing capability and signal polarity, which are critical for interfacing with other logic. |
| Control Inputs | Output Enable (active LOW) per channel | Address inputs (A0, A1) and Enable (active LOW) per decoder | Control input structure defines how the device is driven and sequenced within a system. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | The supply voltage range must match the system rail to ensure reliable operation and logic-level compatibility. |
| Package | SO14 (SOIC-14) | SO16 (SOIC-16) | Package footprint and pin count affect PCB layout and mechanical compatibility; different pin counts prevent direct drop-in replacement. |
| Logic Family | HC (High-speed CMOS) | HC (High-speed CMOS) | Same logic family ensures compatible input thresholds, output drive, and speed characteristics. |
| Operating Temperature Range | -40 °C to +125 °C | -40 °C to +125 °C | Temperature range must cover the application environment for reliable performance. |
| Propagation Delay (typical) | ~11 ns at 4.5 V | ~13 ns at 4.5 V | Propagation delay affects timing margins in high-speed digital circuits. |
| Pin Count | 14 | 16 | Different pin counts mean the devices are not pin-compatible and cannot be swapped without layout changes. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC139D | 74HC125D |
|---|---|---|
| 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 functional differences between the 74HC125D and the 74HC139D?
The 74HC125D contains four independent non-inverting buffers with 3-state outputs, while the 74HC139D contains two independent 2-to-4 line decoders/demultiplexers with active-LOW outputs. They are not functionally equivalent and cannot be used interchangeably.
Are the 74HC125D and 74HC139D pin-compatible?
No. Both use a 16-pin SOIC package, but their pin functions differ. The 74HC125D uses pins for four buffer inputs, four 3-state outputs, and two output-enable pins, while the 74HC139D uses pins for two address inputs, two enable inputs, and eight active-LOW decoder outputs.
Can the 74HC125D and 74HC139D operate from the same supply voltage range?
Yes. Both are 74HC-family CMOS devices specified for a supply voltage range of 2.0 V to 6.0 V, with typical operation at 5.0 V.
What is the logic function of the 74HC125D?
The 74HC125D provides four independent non-inverting buffer gates with 3-state outputs. Each buffer has an active-LOW output enable pin; when enabled, the output follows the input, and when disabled, the output enters a high-impedance state.
What is the logic function of the 74HC139D?
The 74HC139D provides two independent 2-to-4 line decoders/demultiplexers. Each decoder accepts two address inputs and one active-LOW enable input, and produces four mutually exclusive active-LOW outputs.
Are the 74HC125D and 74HC139D interchangeable in a PCB design?
No. Although both are 16-pin SOIC devices in the 74HC family, their internal logic, pin assignments, and output types differ. Substitution requires a complete review of pin functions, signal polarity, and timing against the target design.
Do both devices support 3-state outputs?
No. The 74HC125D has 3-state outputs that can be placed in high-impedance mode via active-LOW enable pins. The 74HC139D has active-LOW decoder outputs that are always driven and do not provide a high-impedance state.