Part A
74HC138D
東芝セミコンダクター・アンド・ストレージ
- Lifecycle
- Active
- Stock
- 2131 個数
- Package
- SOIC-16
- Series
- ロジック - 信号スイッチ、マルチプレクサ、デコーダ
Replacement verdict
Not a drop-in replacement
The 74HC138D and 74HC154D,653 are not functionally interchangeable. The 74HC138D is a 3-to-8 line decoder/demultiplexer with three address inputs and eight mutually exclusive active-LOW outputs, while the 74HC154D,653 is a 4-to-16 line decoder/demultiplexer with four address inputs and sixteen mutually exclusive active-LOW outputs. The differing address bus width, output channel count, and package footprint prevent direct substitution without circuit redesign.
Different channel count
Different address inputs
Different package footprint
Different logic function
Parts at a glance
Part B
74HC154D,653
パナソニック電子部品
- Lifecycle
- Active
- Stock
- 4133 個数
- Package
- SOIC-24
- Series
- ロジック - 信号スイッチ、マルチプレクサ、デコーダ
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HC138D | 74HC154D,653 | Why it matters |
|---|---|---|---|
| Function | 3-to-8 line decoder/demultiplexer | 4-to-16 line decoder/demultiplexer | Defines the decoding width; a 3-to-8 device selects 1 of 8 outputs while a 4-to-16 device selects 1 of 16, so they are not pin-compatible substitutes. |
| Number of Outputs | 8 | 16 | Determines how many peripheral or memory lines can be selected, directly affecting system address space and board routing. |
| Number of Address Inputs | 3 | 4 | Sets the number of select bits required from the host; more inputs allow a larger decode space but need additional control lines. |
| Package / Pin Count | SO16 (16 pins) | SO24 (24 pins) | Different footprints and pin counts prevent drop-in replacement and require PCB layout changes. |
| Enable Inputs | 3 (two active-low, one active-high) | 2 (both active-low) | Enable structure affects cascading, gating logic, and how the device is disabled or expanded in a larger decoder tree. |
| Output Type | Active-low outputs | Active-low outputs | Both sink current when selected, so they interface similarly to loads, but the selected line polarity must match the target logic. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | Compatible logic-level operation across 2 V to 6 V allows use in both 3.3 V and 5 V systems. |
| Logic Family | 74HC CMOS | 74HC CMOS | Same family means comparable input thresholds, noise margins, and drive characteristics, simplifying mixed-family interfacing. |
| Propagation Delay (typical) | Approx. 15 ns at 5 V | Approx. 20 ns at 5 V | Timing differences can affect setup/hold margins in high-speed address decoding and may require timing re-validation. |
| Output Drive Current | ±4 mA at 5 V | ±4 mA at 5 V | Similar drive strength means both can directly drive standard CMOS inputs, but fan-out and load capacitance must still be checked. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC138D | 74HC154D,653 |
|---|---|---|
| Supplier | - | Rochester Electronics, LLC |
| Series | 74HC | 74HC |
| Part Status | Active | Active |
| Type | Decoder/Demultiplexer | Decoder/Demultiplexer |
| Circuit | 1 x 3:8 | 1 x 4:16 |
| Independent Circuits | 1 | 1 |
| Current - Output High Low | 5.2mA, 5.2mA | 5.2mA, 5.2mA |
| Voltage Supply Source | Single Supply | Single Supply |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Operating Temperature | -40°C ~ 125°C | -40°C ~ 125°C |
| Mounting Type | Surface Mount | Surface Mount |
Frequently asked questions
What are the main functional differences between the 74HC138D and the 74HC154D,653?
The 74HC138D is a 3-to-8 line decoder/demultiplexer with three binary select inputs (A0, A1, A2) and eight mutually exclusive active-LOW outputs. The 74HC154D,653 is a 4-to-16 line decoder/demultiplexer with four binary select inputs (A0–A3) and sixteen mutually exclusive active-LOW outputs. Both are HC-family CMOS devices, but the 74HC154D,653 provides twice the output count and requires one additional select input.
Are the 74HC138D and 74HC154D,653 pin-compatible?
No. The 74HC138D is typically supplied in a 16-pin package (SO16 or DIP-16), while the 74HC154D,653 is supplied in a 24-pin package (SO24). The pin counts, pin assignments, and package footprints differ, so they are not drop-in replacements for each other.
What are the supply voltage and logic family specifications for both devices?
Both the 74HC138D and 74HC154D,653 are 74HC-series high-speed CMOS devices. They operate over a supply voltage range of 2.0 V to 6.0 V, with typical operation at 5.0 V. They are compatible with standard CMOS and TTL logic levels when used within the specified supply range.
How do the enable inputs differ between the 74HC138D and the 74HC154D,653?
The 74HC138D has three enable inputs: two active-LOW (E1, E2) and one active-HIGH (E3). All three must be in their active state for the device to decode. The 74HC154D,653 has two active-LOW enable inputs (E1, E2), and both must be LOW for the device to decode. This difference affects how each device is cascaded or gated in a system.
Can the 74HC138D be used to build a 4-to-16 decoder equivalent to the 74HC154D,653?
Yes, two 74HC138D devices can be combined with external logic to form a 4-to-16 decoder. The fourth select bit is used to enable one of the two 74HC138D devices while disabling the other. However, this requires additional components and board space compared to using a single 74HC154D,653, which integrates the full 4-to-16 decoding function in one package.
What are the output drive characteristics of the 74HC138D and 74HC154D,653?
Both devices provide standard 74HC CMOS output drive. They are specified to drive standard CMOS and TTL loads within the 74HC family limits. For exact output current ratings (source and sink), refer to the respective manufacturer datasheets, as these parameters are specified under defined test conditions and may vary slightly between manufacturers.
Which device is more suitable for memory address decoding in a microprocessor system?
The choice depends on the address space size. The 74HC138D is suitable for decoding up to 8 address lines or chip-select regions using 3 select bits. The 74HC154D,653 is suitable for decoding up to 16 regions using 4 select bits. For systems requiring more chip-select outputs without additional glue logic, the 74HC154D,653 is the more direct solution.
Are the 74HC138D and 74HC154D,653 interchangeable in existing designs?
No, they are not directly interchangeable. Differences in pin count, package footprint, number of select inputs, number of outputs, and enable input configuration mean that a direct substitution would require PCB redesign and logic revalidation. Always verify against the specific manufacturer datasheet before considering any replacement.