Part A
74HC139D
Компания Toshiba Semiconductor и Storage
- Lifecycle
- Active
- Stock
- 4290 ПКС
- Package
- SOIC-16
- Series
- Логика - коммутаторы сигнала, мультиплексеры, декодеры
Replacement verdict
Not a drop-in replacement
The 74HC123D and 74HC139D are functionally unrelated logic ICs and cannot serve as substitutes for one another. The 74HC123D is a dual retriggerable monostable multivibrator with timing and pulse-generation functions, while the 74HC139D is a dual 2-to-4 line decoder/demultiplexer with address-decoding functions. Their internal architectures, pin functions, and application roles differ fundamentally, so direct replacement is not feasible in any design.
Different logic function
Different output type
Different pin function
Different application role
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HC123D | 74HC139D | Why it matters |
|---|---|---|---|
| Function | Dual retriggerable monostable multivibrator with reset | Dual 2-to-4 line decoder/demultiplexer | These devices perform completely different logic functions, so they are not functionally interchangeable in a circuit. |
| Logic Type | Monostable multivibrator (one-shot) | Decoder/demultiplexer | The logic type determines the device's role in signal generation versus signal routing/selection. |
| Number of Circuits | 2 | 2 | Both integrate two independent units per package, but each unit performs a different function. |
| Number of Inputs per Circuit | 2 (trigger inputs) plus reset | 2 (address/select inputs) plus enable | Input count and type affect how the device interfaces with surrounding logic and control signals. |
| Number of Outputs per Circuit | 1 (pulse output) with complementary output | 4 (decoded outputs) | Output count and configuration determine fan-out and the number of signals the device can drive. |
| Output Type | Push-pull (CMOS) | Push-pull (CMOS), active low | Output polarity and drive style affect compatibility with downstream logic inputs. |
| Supply Voltage Range | 2 V to 6 V | 2 V to 6 V | Both operate over the standard HC-family supply range, allowing use in similar power environments. |
| Propagation Delay | Typically ~25 ns at 4.5 V | Typically ~14 ns at 4.5 V | Propagation delay influences timing margins and maximum operating frequency in the target design. |
| Package | SO16 (SOIC-16) | SO16 (SOIC-16) | Matching package and pin count simplifies PCB footprint compatibility, though pinouts differ. |
| Operating Temperature Range | -40 °C to +125 °C | -40 °C to +125 °C | Both support industrial temperature ranges, making them suitable for similar environmental conditions. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC139D | 74HC123D |
|---|---|---|
| Series | 74HC | 74HC |
| Part Status | Obsolete | Active |
| Type | Decoder/Demultiplexer | - |
| Circuit | 1 x 2:4 | - |
| Independent Circuits | 2 | 2 |
| Current - Output High Low | 5.2mA, 5.2mA | 5.2mA, 5.2mA |
| Voltage Supply Source | Single Supply | - |
| Voltage - Supply | 2V ~ 6V | 2 V ~ 6 V |
| Operating Temperature | -40°C ~ 85°C | -40°C ~ 85°C |
| Mounting Type | Surface Mount | Surface Mount |
| Logic Type | - | Monostable |
| Schmitt Trigger Input | - | Yes |
| Propagation Delay | - | 40 ns |
Frequently asked questions
What are the primary functions of the 74HC123D and 74HC139D?
The 74HC123D is a dual retriggerable monostable multivibrator that generates a single output pulse of a specified width for each trigger input. The 74HC139D is a dual 2-to-4 line decoder/demultiplexer that routes one of four outputs low based on a 2-bit binary address.
Can the 74HC123D and 74HC139D be used interchangeably in a circuit?
No. They perform fundamentally different logic functions. The 74HC123D is a timing device for pulse generation, while the 74HC139D is a combinational logic decoder/demultiplexer. Substitution requires a complete redesign of the surrounding circuit.
Do the 74HC123D and 74HC139D share the same package and pinout?
Both devices are commonly offered in a 16-pin SOIC package (the "D" suffix in 74HC123D and 74HC139D typically denotes SOIC). However, their pinouts are not identical because their internal functions and input/output requirements differ. Always verify the specific pin assignment from the manufacturer datasheet before layout.
What are the key timing specifications for the 74HC123D?
The 74HC123D output pulse width is set by an external resistor (REXT) and capacitor (CEXT) according to the formula tW ≈ K × REXT × CEXT, where K is typically 0.45 to 0.55 for the HC family. It supports retriggering and has a trigger propagation delay typically in the range of 20–30 ns at 5 V.
What are the key propagation delays for the 74HC139D?
The 74HC139D typically has a propagation delay from address inputs (A0, A1) to outputs (Y0–Y3) of about 15–20 ns at 5 V, and from enable inputs (E1, E2) to outputs of about 12–18 ns at 5 V. These values vary with supply voltage and load capacitance.
Are both the 74HC123D and 74HC139D compatible with 5 V and 3.3 V logic systems?
Both are 74HC series devices, which typically operate over a supply voltage range of 2 V to 6 V. They are therefore compatible with both 5 V and 3.3 V logic levels when used within that range, but input threshold voltages and output drive strengths must be checked against the specific datasheet for the target supply voltage.
Which device is better for generating a delayed pulse, and which for selecting one of several outputs?
The 74HC123D is the correct choice for generating a delayed or retriggerable pulse because it is a monostable multivibrator. The 74HC139D is the correct choice for selecting one of four outputs based on a binary address because it is a decoder/demultiplexer.
Do the 74HC123D and 74HC139D have the same output drive capability?
Both are standard 74HC CMOS devices and typically provide symmetrical output drive of about ±4 mA at 5 V. However, actual drive current depends on the specific manufacturer and supply voltage. Always consult the datasheet for the exact output current ratings.