Part A
74HC138D
Toshiba Semiconductor and Storage
- Lifecycle
- Active
- Stock
- 2131 PCS
- Package
- SOIC-16
- Series
- Logic - Signal Switches, Multiplexers, Decoders
Replacement verdict
Not a drop-in replacement
The 74HC138D and 74HC165D,653 are functionally unrelated logic ICs and cannot serve as substitutes for one another. The 74HC138D is a 3-to-8 line decoder/demultiplexer with active-low outputs, while the 74HC165D,653 is an 8-bit parallel-in/serial-out shift register. Their differing logic functions, pinouts, and I/O configurations make direct replacement impossible without complete circuit redesign.
Different logic function
Different pinout
Different I/O direction
Different output type
Parts at a glance
Part B
74HC165D,653
Nexperia USA Inc.
- Lifecycle
- Active
- Stock
- 9205 PCS
- Series
- Logic - Shift Registers
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 | 74HC165D,653 | Why it matters |
|---|---|---|---|
| Logic Function | 3-to-8 line decoder/demultiplexer | 8-bit parallel-in/serial-out shift register | Defines the core function; these devices perform fundamentally different operations and are not functionally interchangeable. |
| Number of Pins | 16 | 16 | Pin count affects package footprint and PCB layout compatibility. |
| Package / Case | SOIC-16 (SOT109-1) | SOIC-16 (SOT109-1) | Same package allows drop-in mechanical compatibility on an existing PCB footprint. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | Determines compatibility with the system power rail and logic level family. |
| Output Type | Active-LOW decoded outputs (8) | Serial output (Q7, Q7bar) with parallel inputs | Output behavior dictates how the device interfaces with downstream logic or loads. |
| Number of Inputs | 3 address inputs plus 3 enable inputs | 8 parallel data inputs plus control inputs | Input count and type determine how many signals the device can accept and process. |
| Propagation Delay (typical) | ~14 ns at 4.5 V | ~14 ns at 4.5 V | Affects maximum operating frequency and timing margins in the system. |
| Operating Temperature Range | -40 °C to +125 °C | -40 °C to +125 °C | Ensures the device meets the environmental requirements of the target application. |
| Logic Family | 74HC (High-speed CMOS) | 74HC (High-speed CMOS) | Same logic family ensures compatible input thresholds and output drive levels. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC138D | 74HC165D,653 |
|---|---|---|
| Series | 74HC | 74HC |
| Part Status | Active | Active |
| Logic Type | - | Shift Register |
| Output Type | - | Complementary |
| Number of Elements | - | 1 |
| Number of Bits per Element | - | 8 |
| Function | - | Parallel or Serial to Serial |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Operating Temperature | -40°C ~ 125°C | -40°C ~ 125°C |
| Mounting Type | Surface Mount | Surface Mount |
| Base Product Number | - | 74HC165 |
| Type | Decoder/Demultiplexer | - |
| Circuit | 1 x 3:8 | - |
| Independent Circuits | 1 | - |
| Current - Output High Low | 5.2mA, 5.2mA | - |
| Voltage Supply Source | Single Supply | - |
Frequently asked questions
What are the primary functional differences between the 74HC138D and the 74HC165D,653?
The 74HC138D is a 3-to-8 line decoder/demultiplexer that takes three binary select inputs and activates one of eight mutually exclusive outputs. The 74HC165D,653 is an 8-bit parallel-in/serial-out shift register that loads eight parallel data bits and shifts them out serially. They perform fundamentally different logic functions and are not interchangeable.
Are the 74HC138D and 74HC165D,653 pin-compatible?
No. The 74HC138D is typically supplied in a 16-pin SOIC package with inputs A0, A1, A2, enable inputs E1, E2, E3, and outputs Y0 through Y7. The 74HC165D,653 is supplied in a 16-pin SOIC package with parallel data inputs D0 through D7, serial input DS, clock, shift/load, and complementary serial outputs Q7 and Q7. The pin functions and assignments differ, so they cannot be used as drop-in replacements for each other.
Can the 74HC138D and 74HC165D,653 operate from the same supply voltage?
Yes. Both devices are members of the 74HC logic family and are specified for a nominal supply voltage range of 2.0 V to 6.0 V, with 5 V being the most common operating condition. This allows them to be used in the same 3.3 V or 5 V logic system without level shifting between them.
What is the function of the enable inputs on the 74HC138D compared with the control inputs on the 74HC165D,653?
The 74HC138D has three enable inputs (two active-low and one active-high) that must all be asserted for the selected output to become active. The 74HC165D,653 uses a shift/load input to select between parallel loading and serial shifting, and a clock input to advance the shift register. These control schemes serve different purposes and are not equivalent.
Which device is suitable for expanding the number of inputs to a microcontroller?
The 74HC165D,653 is the appropriate choice for input expansion because it captures eight parallel input bits and shifts them serially into a microcontroller, reducing the required pin count. The 74HC138D is intended for output decoding or demultiplexing, not for input expansion.
Which device is suitable for selecting one of eight peripheral devices or memory banks?
The 74HC138D is suitable for this application because its 3-to-8 decoding function activates exactly one of eight outputs based on a 3-bit address, which is commonly used for chip-select or address decoding. The 74HC165D,653 does not provide address decoding and cannot perform this function.
Do both devices support the same operating temperature range?
Both the 74HC138D and the 74HC165D,653 are typically specified for the industrial temperature range of -40 °C to +125 °C or -40 °C to +85 °C depending on the exact manufacturer and suffix. Designers should confirm the specific ordering part number and datasheet because temperature grades can vary between suppliers.
Can the 74HC138D and 74HC165D,653 be used together in the same design?
Yes. Because both are 74HC-family devices with compatible supply voltage ranges and logic levels, they can be used together. A common configuration uses the 74HC138D for address decoding or output selection while the 74HC165D,653 handles parallel-to-serial input acquisition, with both sharing the same logic supply and ground.