Part A
74HC238D
Компания Toshiba Semiconductor и Storage
- Lifecycle
- Active
- Stock
- 5394 ПКС
- Package
- SOIC-16
- Series
- Логика - коммутаторы сигнала, мультиплексеры, декодеры
Replacement verdict
Not a drop-in replacement
The 74HC238D and 74HC244D,653 are functionally unrelated ICs: one is a 3-to-8 line decoder/demultiplexer and the other is an octal non-inverting buffer/line driver with 3-state outputs. They differ in logic function, channel count, output type, and pinout, so neither device can substitute for the other in an existing design.
Different logic function
Different channel count
Different output type
Different pinout
Parts at a glance
Part B
74HC244D,653
Компания NXP USA Inc.
- Lifecycle
- Active
- Stock
- 6812 ПКС
- Package
- SOIC-20
- Series
- Логика - буферы, драйверы, приемники, передатчики
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 | 74HC244D,653 | Why it matters |
|---|---|---|---|
| Logic Function | 3-to-8 Line Decoder / Demultiplexer | Octal Buffer / Line Driver (3-State) | The core function differs fundamentally; one decodes binary inputs to one of eight outputs, while the other buffers eight signals. They are not functionally interchangeable. |
| Number of Outputs | 8 (active-LOW, one selected at a time) | 8 (independent, 3-state) | Although both have eight outputs, the decoder activates only one output per input combination, whereas the buffer drives all outputs independently. |
| Output Type | Active-LOW, non-3-state | 3-State (high-impedance capable) | 3-state outputs allow bus sharing and isolation; the decoder's outputs cannot be placed in high-impedance, limiting bus applications. |
| Number of Inputs | 3 address inputs plus 3 enable inputs | 8 data inputs plus 2 output-enable inputs | Input count and configuration determine how the device interfaces with surrounding logic and control signals. |
| Propagation Delay (typical at 5V) | Approximately 14 ns | Approximately 13 ns | Timing affects maximum operating frequency and signal integrity in synchronous systems; similar but not identical delays may matter in tight timing budgets. |
| Output Drive Current (per output) | ±4 mA (standard HC drive) | ±6 mA (standard HC drive) | Drive current determines fan-out and ability to drive loads such as LEDs or long traces; the buffer offers slightly higher drive. |
| Supply Voltage Range | 2 V to 6 V | 2 V to 6 V | Both support the standard HC supply range, allowing use in 3.3 V and 5 V systems. |
| Package | SO16 (SOIC-16) | SO20 (SOIC-20) | 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, suitable for harsh environments. |
| Logic Family | 74HC (High-Speed CMOS) | 74HC (High-Speed CMOS) | Same logic family ensures compatible input thresholds and output levels, but the differing functions still prevent direct substitution. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC238D | 74HC244D,653 |
|---|---|---|
| Supplier | - | Rochester Electronics, LLC |
| Series | 74HC | 74HC |
| Part Status | Active | Active |
| Logic Type | - | Buffer, Non-Inverting |
| Number of Elements | - | 2 |
| Number of Bits per Element | - | 4 |
| Output Type | - | 3-State |
| Current - Output High Low | 5.2mA, 5.2mA | 7.8mA, 7.8mA |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Operating Temperature | -40°C ~ 125°C | -40°C ~ 125°C (TA) |
| Mounting Type | Surface Mount | Surface Mount |
| Type | Decoder/Demultiplexer | - |
| Circuit | 1 x 3:8 | - |
| Independent Circuits | 1 | - |
| Voltage Supply Source | Single Supply | - |
Frequently asked questions
What are the primary functional differences between the 74HC238D and the 74HC244D,653?
The 74HC238D is a 3-to-8 line decoder/demultiplexer that takes a 3-bit binary address and activates one of eight mutually exclusive outputs. The 74HC244D,653 is an octal non-inverting buffer/line driver with 3-state outputs, designed to drive bus lines or buffer memory address registers. They serve entirely different logic functions and are not functionally interchangeable.
Are the 74HC238D and 74HC244D,653 pin-compatible?
No. Both devices are typically offered in a 16-pin SOIC package, but their pinouts differ. The 74HC238D assigns pins to address inputs (A0, A1, A2), enable inputs (E1, E2, E3), and eight decoded outputs (Y0–Y7). The 74HC244D,653 assigns pins to eight data inputs (A1–A8), eight data outputs (Y1–Y8), and two output-enable pins (1OE, 2OE). Direct PCB substitution is not possible without layout changes.
Can the 74HC238D and 74HC244D,653 operate from the same supply voltage?
Yes. Both are 74HC-family CMOS devices and are specified for a standard operating supply voltage range of 2.0 V to 6.0 V, with typical use at 5.0 V. This shared supply range allows them to coexist in the same logic system without level-shifting.
What is the difference in output drive capability between the 74HC238D and the 74HC244D,653?
The 74HC244D,653 is specified with a higher output drive capability, typically ±6 mA at 5 V, making it suitable for bus driving and line buffering. The 74HC238D provides standard 74HC-family output drive, typically ±4 mA at 5 V, which is adequate for driving standard CMOS or TTL inputs but not heavy bus loads.
Does the 74HC244D,653 have 3-state outputs while the 74HC238D does not?
Correct. The 74HC244D,653 features 3-state outputs controlled by two active-low output-enable pins (1OE and 2OE), allowing its outputs to be placed in a high-impedance state for bus sharing. The 74HC238D has standard push-pull outputs with no high-impedance state; its outputs are either HIGH or LOW depending on the address and enable inputs.
Can the 74HC238D be used to drive the inputs of a 74HC244D,653?
Yes. The 74HC238D outputs are standard CMOS push-pull and can directly drive the inputs of the 74HC244D,653, provided both devices operate from the same supply voltage and the fan-out limits of the 74HC238D are respected. This combination is common when decoded select signals need to be buffered before driving a bus or cable.
What are the typical propagation delay differences between the 74HC238D and the 74HC244D,653?
At a 5 V supply and 25 °C, the 74HC238D typically exhibits a propagation delay from address input to output of approximately 14 ns to 20 ns. The 74HC244D,653 typically exhibits a propagation delay from data input to output of approximately 10 ns to 15 ns. Exact values depend on load capacitance and supply voltage, and should be verified against the respective manufacturer datasheets.
Are the 74HC238D and 74HC244D,653 interchangeable in a multiplexed bus application?
No. The 74HC238D is a decoder/demultiplexer that selects one of eight outputs based on a binary address, while the 74HC244D,653 is an octal buffer with 3-state outputs intended for bidirectional or shared bus interfacing. Replacing one with the other would require redesigning the logic function, enable scheme, and bus control, and cannot be done as a direct drop-in substitution.