Part A
74HC238D
東芝電晶體與存儲
- Lifecycle
- Active
- Stock
- 5394 件
- Package
- SOIC-16
- Series
- 邏輯-訊號開關、多工器、解碼器
Replacement verdict
Not a drop-in replacement
The 74HC238D and 74HC273D,652 are functionally unrelated ICs: one is a 3-to-8 line decoder/demultiplexer and the other is an octal D-type flip-flop. They differ in logic function, input/output architecture, latching behavior, and pinout, so neither device can substitute for the other in an existing design.
Different logic function
Different output type
Different latching behavior
Different pinout
Parts at a glance
Part B
74HC273D,652
恩智浦電晶體
- Lifecycle
- Active
- Stock
- 6122 件
- Series
- 邏輯-觸發器
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HC238D | 74HC273D,652 | Why it matters |
|---|---|---|---|
| Logic Function | 3-to-8 Line Decoder / Demultiplexer | Octal D-Type Flip-Flop with Reset | Defines the core function; these devices are not functionally interchangeable as they perform completely different logic operations. |
| Output Type | Active-Low outputs (8) | Non-inverted D flip-flop outputs (8) | Output polarity and behavior determine how the device interfaces with downstream logic. |
| Number of Inputs | 3 address inputs plus 3 enable inputs | 8 data inputs plus clock and reset | Input count and type dictate the control signals and data path required in a design. |
| Clock Requirement | Combinational (no clock) | Edge-triggered clock input | Clocked devices store state, while combinational devices respond immediately to inputs, affecting timing and sequential logic design. |
| Reset Function | No reset (has enable inputs instead) | Asynchronous master reset | Reset capability is essential for initializing flip-flops to a known state at power-up. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | Both support the standard HC-family supply range, allowing use in 3.3 V and 5 V systems. |
| Logic Family | 74HC (High-speed CMOS) | 74HC (High-speed CMOS) | Same logic family ensures compatible input/output voltage thresholds and drive characteristics. |
| Package | SO16 (16-pin SOIC) | SO20 (20-pin SOIC) | Different pin counts and footprints prevent direct drop-in replacement on the same PCB pad layout. |
| Operating Temperature Range | -40 °C to +125 °C | -40 °C to +125 °C | Both meet industrial temperature requirements for reliable operation in harsh environments. |
| Propagation Delay (typical at 5 V) | Approximately 14 ns | Approximately 15 ns (clock to output) | Timing characteristics affect maximum operating frequency and signal integrity in synchronous designs. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC238D | 74HC273D,652 |
|---|---|---|
| Supplier | - | Rochester Electronics, LLC |
| Series | 74HC | Bulk |
| Function | - | Active |
| Part Status | Active | - |
| Type | Decoder/Demultiplexer | - |
| Circuit | 1 x 3:8 | - |
| Independent Circuits | 1 | - |
| Current - Output High Low | 5.2mA, 5.2mA | - |
| Voltage Supply Source | Single Supply | - |
| Voltage - Supply | 2V ~ 6V | - |
| Operating Temperature | -40°C ~ 125°C | - |
| Mounting Type | Surface Mount | - |
Frequently asked questions
What are the primary functional differences between the 74HC238D and the 74HC273D,652?
The 74HC238D is a 3-to-8 line decoder/demultiplexer that routes one input to one of eight outputs based on a 3-bit address, while the 74HC273D,652 is an octal D-type flip-flop that stores and outputs 8 bits of data on a clock edge. They serve fundamentally different logic functions and are not interchangeable.
Do the 74HC238D and 74HC273D,652 have the same package and pinout?
Both devices are typically offered in a 16-pin SOIC package (the "D" suffix in 74HC238D and the "652" suffix in 74HC273D,652 denotes SOIC-16). However, their pinouts differ because their internal logic functions are different, so they are not pin-to-pin compatible.
Can the 74HC238D be used as a direct substitute for the 74HC273D,652 in an existing design?
No. The 74HC238D is a combinational decoder/demultiplexer with no data storage, whereas the 74HC273D,652 is an edge-triggered octal flip-flop with data retention. Substitution would require a complete redesign of the surrounding logic and timing.
What are the key electrical characteristics of the 74HC238D?
The 74HC238D operates from a 2.0 V to 6.0 V supply, has standard CMOS input thresholds, and provides eight active-low outputs (Y0–Y7) with a typical propagation delay of approximately 12 ns at 4.5 V. It includes three enable inputs (two active-low, one active-high) for cascading.
What are the key electrical characteristics of the 74HC273D,652?
The 74HC273D,652 operates from a 2.0 V to 6.0 V supply, features eight positive-edge-triggered D-type flip-flops with individual D inputs and Q outputs, and includes a common asynchronous master reset (MR). Typical maximum clock frequency is 60 MHz at 4.5 V.
Are the 74HC238D and 74HC273D,652 compatible with 3.3 V logic systems?
Yes. Both devices are specified for operation from 2.0 V to 6.0 V, so they can be powered from a 3.3 V rail. However, input voltage levels must be verified against the VIH/VIL specifications for the chosen supply voltage to ensure proper logic thresholds.
Which device is better suited for address decoding in a microprocessor system?
The 74HC238D is the appropriate choice for address decoding because it accepts a 3-bit binary address and activates one of eight outputs, enabling chip-select or memory-mapped I/O selection. The 74HC273D,652 is intended for data latching or storage, not address decoding.
Which device is better suited for temporary data storage or output port expansion?
The 74HC273D,652 is designed for temporary data storage and output port expansion because its octal flip-flops capture and hold 8 bits on a clock edge. The 74HC238D cannot store data and therefore is not suitable for this function.