Part A
74HC151D
Toshiba Semiconductor et stockage
- Lifecycle
- Active
- Stock
- 3388 PCS
- Package
- SOIC-16
- Series
- Logique - commutateurs de signaux, multiplexeurs, décodeurs
Replacement verdict
Not a drop-in replacement
The 74HC123D and 74HC151D serve fundamentally different logic functions and cannot be used interchangeably in existing designs. The 74HC123D is a dual retriggerable monostable multivibrator for pulse generation, while the 74HC151D is an 8-to-1 multiplexer for data selection. Their divergent functional architectures, pin assignments, and signal path requirements make direct substitution impossible without complete circuit redesign.
Different logic function
Different pin assignment
Different input configuration
Different output behavior
Parts at a glance
Part B
74HC123D
NXP USA Inc.
- Lifecycle
- Active
- Stock
- 3320 PCS
- Package
- SOIC-16
- Series
- Logique - multivibrateurs
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 | 74HC151D | Why it matters |
|---|---|---|---|
| Function | Dual retriggerable monostable multivibrator with reset | Single 8-input multiplexer | The core logic function differs completely, so these parts are not functionally interchangeable in a circuit. |
| Logic Type | Monostable multivibrator | Data selector/multiplexer | Determines the signal-processing behavior and the role the IC plays in the system. |
| Number of Circuits | 2 | 1 | Affects how many independent channels or functions can be implemented with one package. |
| Number of Inputs per Circuit | 2 (trigger inputs) plus reset | 8 data inputs plus 3 select inputs | Input count defines the interfacing requirements and the complexity of the surrounding circuit. |
| Number of Outputs per Circuit | 2 (Q and complementary Q) | 1 (Y) plus complementary output | Output configuration affects signal routing and whether inverted outputs are available. |
| Propagation Delay | Typically around 20 ns at 5 V | Typically around 14 ns at 5 V | Timing performance influences maximum operating frequency and system speed margins. |
| Supply Voltage Range | 2 V to 6 V | 2 V to 6 V | Both support standard HC-family supply rails, but the functional difference still prevents direct substitution. |
| Package Type | SOIC-16 | SOIC-16 | Matching package and pin count can allow board-level compatibility, but pin functions must still be verified. |
| Pin Count | 16 | 16 | Same pin count does not guarantee pinout compatibility, especially for different logic functions. |
| Operating Temperature Range | -40 °C to +125 °C | -40 °C to +125 °C | Both are suitable for industrial temperature environments, but this does not overcome the functional mismatch. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC151D | 74HC123D |
|---|---|---|
| Series | 74HC | 74HC |
| Part Status | Active | Active |
| Type | Multiplexer | - |
| Circuit | 1 x 8:1 | - |
| Independent Circuits | 1 | 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 ~ 125°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 74HC151D?
The 74HC123D is a dual retriggerable monostable multivibrator that generates output pulses of a defined width determined by external resistor and capacitor values. The 74HC151D is an 8-input digital multiplexer that selects one of eight data inputs based on a 3-bit binary address and routes it to a single output.
Can the 74HC123D and 74HC151D be used interchangeably in a circuit?
No. They perform fundamentally different logic functions. The 74HC123D is a timing device for pulse generation, while the 74HC151D is a data selection device. Substitution requires a complete redesign of the surrounding circuit.
Do the 74HC123D and 74HC151D share the same package and pinout?
Both devices are typically offered in a 16-pin SOIC package (the "D" suffix in NXP and similar naming conventions). However, their pin functions differ entirely. The 74HC123D uses pins for trigger inputs, reset, external timing components, and outputs, while the 74HC151D uses pins for eight data inputs, three select inputs, an enable input, and complementary outputs.
What are the key timing specifications for the 74HC123D?
The 74HC123D output pulse width is set by an external resistor (R_ext) and capacitor (C_ext) according to the approximate formula t_W = K × R_ext × C_ext, where K is typically 0.45 to 0.55 for the HC family. It supports retriggering, meaning a new trigger pulse during the output pulse extends the pulse width. Exact limits must be verified from the manufacturer datasheet.
What are the key selection specifications for the 74HC151D?
The 74HC151D selects one of eight data inputs (D0–D7) based on the 3-bit address inputs (A, B, C). It features a strobe/enable input that forces the output low when inactive. Propagation delay and input/output voltage levels are specified in the manufacturer datasheet for the 74HC family.
Are both devices compatible with standard 74HC logic levels?
Yes. Both the 74HC123D and 74HC151D are members of the 74HC CMOS logic family and operate with standard 2 V to 6 V supply voltages, with input and output levels compatible with other 74HC and many 74LS devices under proper conditions.
Which device is suitable for debouncing a mechanical switch?
The 74HC123D is suitable for switch debouncing because its monostable action can generate a single clean output pulse from a noisy input edge. The 74HC151D is not intended for debouncing; it is a multiplexer for data selection.
Can the 74HC151D be used to expand the input count of a microcontroller?
Yes. The 74HC151D can multiplex eight digital signals into one output, allowing a microcontroller to read multiple inputs using only three address lines and one data line. The 74HC123D cannot perform this function.