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 74HC139D and 74HC166D are functionally unrelated logic ICs and cannot serve as substitutes for one another. The 74HC139D is a dual 2-to-4 line decoder/demultiplexer, while the 74HC166D is an 8-bit parallel-in/serial-out shift register. Their internal architectures, pin functions, and logic operations differ fundamentally, making direct replacement impossible without complete circuit redesign.
Different logic function
Different input/output configuration
Different pin function assignment
Different sequential vs combinational operation
Parts at a glance
Part B
74HC166D
Toshiba Semiconductor and Storage
- Lifecycle
- Active
- Stock
- 8001 PCS
- Package
- SOIC-16
- Series
- Lógica - Registos de Maiúsculas
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HC139D | 74HC166D | Why it matters |
|---|---|---|---|
| Function | Dual 2-to-4 line decoder/demultiplexer | 8-bit parallel-in/serial-out shift register | The core logic function differs, so these devices are not functionally interchangeable in a circuit. |
| Logic Type | Decoder/Demultiplexer | Shift Register | Determines the signal-processing role of the IC within a digital system. |
| Number of Circuits | 2 | 1 | Affects how many independent decoding or shifting operations can be performed per package. |
| Number of Inputs per Circuit | 2 address inputs per decoder | 9 (8 parallel data plus shift/load control) | Input count defines the data width and control complexity supported by the device. |
| Number of Outputs per Circuit | 4 | 1 serial output (plus QH' complement) | Output configuration determines how the device drives downstream logic or data lines. |
| Output Type | Active-low decoded outputs | Serial data output | Output polarity and format must match the receiving circuit for correct operation. |
| Supply Voltage Range | 2 V to 6 V | 2 V to 6 V | Both support standard HC-family supply levels, allowing use in similar logic rails. |
| Propagation Delay | Typically ~14 ns at 4.5 V | Typically ~15 ns at 4.5 V | Timing affects maximum operating frequency and signal integrity in synchronous designs. |
| Package | SOIC-16 | SOIC-16 | Matching package and pin count simplifies PCB footprint compatibility, though pinout functions differ. |
| Operating Temperature Range | -40 °C to +125 °C | -40 °C to +125 °C | Both are suitable for industrial temperature environments. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC139D | 74HC166D |
|---|---|---|
| Supplier | - | Toshiba Semiconductor and Storage |
| Series | 74HC | 74HC |
| Part Status | Obsolete | Active |
| Logic Type | - | Shift Register |
| Output Type | - | Push-Pull |
| Number of Elements | - | 1 |
| Number of Bits per Element | - | 8 |
| Function | - | Parallel or Serial to Serial |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Operating Temperature | -40°C ~ 85°C | -40°C ~ 125°C |
| Mounting Type | Surface Mount | Surface Mount |
| Type | Decoder/Demultiplexer | - |
| Circuit | 1 x 2:4 | - |
| Independent Circuits | 2 | - |
| Current - Output High Low | 5.2mA, 5.2mA | - |
| Voltage Supply Source | Single Supply | - |
Frequently asked questions
What are the primary functions of the 74HC139D and 74HC166D?
The 74HC139D is a dual 2-to-4 line decoder/demultiplexer, while the 74HC166D is an 8-bit parallel-in/serial-out shift register. They serve fundamentally different logic functions and are not interchangeable.
Can the 74HC139D and 74HC166D be used as direct substitutes for each other?
No. The 74HC139D performs address decoding or demultiplexing with two independent 2-to-4 decoders, whereas the 74HC166D performs serial data shifting with parallel load capability. Their pin functions and internal logic are incompatible for direct substitution.
Do the 74HC139D and 74HC166D share the same package and pinout?
Both devices are typically offered in a 16-pin SOIC package (the "D" suffix in Nexperia naming denotes SOIC). However, their pinouts differ because the 74HC139D uses pins for two separate decoders, while the 74HC166D uses pins for parallel inputs, serial input, clock, and control signals.
What are the key control inputs for the 74HC139D?
The 74HC139D has two independent decoders, each with two address inputs (A0, A1) and one active-LOW enable input (E). When enabled, the selected output goes LOW while the other three outputs remain HIGH.
What are the key control inputs for the 74HC166D?
The 74HC166D has a parallel load input (PL), a clock input (CP), a serial data input (DS), and an output enable input (OE). It also has eight parallel data inputs (D0–D7) and a serial output (Q7).
Are the 74HC139D and 74HC166D compatible with standard HC-family logic levels?
Yes. Both devices are members of the 74HC CMOS logic family and operate with standard HC input and output voltage thresholds when powered from a 2 V to 6 V supply, as specified in their respective manufacturer datasheets.
Can the 74HC139D and 74HC166D be used together in the same design?
Yes. They can be used together because they perform complementary functions. For example, a 74HC139D can decode address lines to generate chip-select signals, while a 74HC166D can capture parallel data and shift it out serially to a microcontroller or communication interface.
What supply voltage range do the 74HC139D and 74HC166D support?
Both devices are specified for operation from 2 V to 6 V DC, consistent with the standard 74HC logic family. Actual limits and recommended operating conditions should be confirmed from the specific manufacturer datasheet.