Part A
74HC138D
Компания Toshiba Semiconductor и Storage
- Lifecycle
- Active
- Stock
- 2131 ПКС
- Package
- SOIC-16
- Series
- Логика - коммутаторы сигнала, мультиплексеры, декодеры
Replacement verdict
Not a drop-in replacement
The 74HC138D and 74HC154D,652 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,652 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,652
Компания NXP USA Inc.
- Lifecycle
- Active
- Stock
- 2528 ПКС
- Package
- SOIC-24
- Series
- Логика - коммутаторы сигнала, мультиплексеры, декодеры
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,652 | 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 8 outputs while a 4-to-16 device selects 16, so they are not directly interchangeable in address decoding depth. |
| Number of Outputs | 8 | 16 | Determines how many peripheral or memory lines can be selected; the 74HC154D,652 can drive twice as many outputs. |
| Number of Address Inputs | 3 | 4 | Affects the required address bus width and the decoding range; the 74HC154D,652 needs one additional address line. |
| Enable Inputs | 3 (two active-low, one active-high) | 2 (both active-low) | Enable configuration affects cascading and board-level control logic; the 74HC138D offers more flexible enable gating. |
| Output Type | Active-low | Active-low | Both provide active-low outputs, so polarity is compatible, but the selected output count differs. |
| Package | SO16 | SO24 | Footprint and pin count differ, so PCB layout and assembly are not drop-in compatible. |
| Pin Count | 16 | 24 | A different pin count means the devices cannot share the same socket or land pattern. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | Both support common 2 V to 6 V HC-family logic levels, so supply compatibility is generally maintained. |
| Propagation Delay | Typically about 15 ns at 4.5 V | Typically about 20 ns at 4.5 V | Timing differences can affect high-speed address decoding and setup/hold margins. |
| Logic Family | HC | HC | Same logic family means compatible input thresholds and output drive characteristics, but function and pinout still differ. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC138D | 74HC154D,652 |
|---|---|---|
| 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 primary functional differences between the 74HC138D and the 74HC154D,652?
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,652 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,652 provides twice the output count and requires one additional address line.
Are the 74HC138D and 74HC154D,652 pin-compatible?
No. The 74HC138D is typically supplied in a 16-pin package (SO16 or DIP-16), while the 74HC154D,652 is supplied in a 24-pin package (SO24 or DIP-24). The 74HC154D,652 has additional address inputs and eight more outputs, so the pin counts and pin functions differ. They cannot be interchanged on the same PCB footprint without redesign.
What are the supply voltage and logic family specifications for both devices?
Both the 74HC138D and 74HC154D,652 are 74HC high-speed CMOS devices. They operate from a nominal supply voltage (VCC) of 2.0 V to 6.0 V, with 5 V being the typical operating condition. They are compatible with LSTTL input thresholds when operated at 5 V, and both feature standard CMOS noise margins and low power consumption.
How do the enable/control inputs differ between the 74HC138D and 74HC154D,652?
The 74HC138D has three enable inputs: two active-LOW (E1, E2) and one active-HIGH (E3). All three must be in their active state to enable the selected output. The 74HC154D,652 has two active-LOW enable inputs (E1, E2), both of which must be LOW to enable decoding. This difference affects how each device is cascaded or gated in a system.
Can the 74HC138D be used to expand the 74HC154D,652 to decode more than 16 lines?
Yes, in principle. Because the 74HC154D,652 has active-LOW enable inputs, additional 74HC154D,652 devices can be enabled by the outputs of a 74HC138D or similar decoder to build a larger decoder tree. However, the exact wiring and timing must be validated against the propagation delays and fan-out specifications in the respective manufacturer datasheets.
What are the typical propagation delay and output drive characteristics of these devices?
Both devices are 74HC-family parts and typically exhibit propagation delays in the range of approximately 10 ns to 20 ns at 5 V VCC, depending on load and manufacturer. Standard 74HC outputs typically sink or source around 4 mA to 5.2 mA at 5 V, which is sufficient for driving LSTTL or CMOS inputs but not high-current loads such as LEDs without external buffering. Exact values must be taken from the specific manufacturer datasheet.
Which device is more suitable for memory address decoding in an 8-bit system?
The 74HC138D is commonly used for 8-bit address decoding because its 3-to-8 structure matches the lower three address lines and provides eight chip-select outputs. The 74HC154D,652 is more appropriate when 16 select lines are required, such as in larger memory arrays or I/O expansion. The choice depends on the number of address lines and the required number of decoded outputs in the target design.
Do both devices have the same operating temperature range and package options?
Both are typically offered in commercial and industrial temperature grades, with industrial versions commonly rated from -40 °C to +85 °C or -40 °C to +125 °C depending on the manufacturer. Package options differ: the 74HC138D is commonly available in SO16 and DIP-16, while the 74HC154D,652 is commonly available in SO24 and DIP-24. Specific temperature grades and package variants must be confirmed from the manufacturer datasheet for the exact orderable part number.