Part A
74HC594D
Toshiba Semiconductor et stockage
- Lifecycle
- Active
- Stock
- 1976 PCS
- Package
- SOIC-16
- Series
- Logique - Registre à décalage
Replacement verdict
Not a drop-in replacement
The 74HC540D and 74HC594D are not functionally interchangeable. The 74HC540D is an inverting octal buffer/line driver with 3-state outputs, while the 74HC594D is an 8-bit serial-in/parallel-out shift register with output latches. Their logic functions, pinouts, and control interfaces differ fundamentally, so substitution requires a complete circuit redesign rather than a direct swap.
Different logic function
Different output type
Different pinout
Different control interface
Parts at a glance
Part B
74HC540D
Toshiba Semiconductor et stockage
- Lifecycle
- Active
- Stock
- 5312 PCS
- Package
- SOIC-20
- Series
- Logique - Buffers, lecteurs, récepteurs, émetteurs - récepteurs
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HC540D | 74HC594D | Why it matters |
|---|---|---|---|
| Logic Function | Octal buffer/line driver with 3-state outputs (inverting) | 8-bit serial-in/parallel-out shift register with output latches | The core function differs fundamentally; one buffers/drives signals while the other shifts and stores serial data, so they are not functionally interchangeable. |
| Output Type | 3-state inverting | Parallel register outputs (non-inverting) | Output behavior determines how the device interfaces with a bus or load; 3-state allows bus sharing, while register outputs hold latched data. |
| Number of Outputs | 8 | 8 | Both provide eight outputs, but their data paths and control signals differ, affecting substitutability. |
| Control Inputs | Output enable (OE1, OE2) | Serial input, shift clock, latch clock, output enable, reset | Different control schemes mean the surrounding circuitry and timing must be redesigned if swapping parts. |
| Data Direction | Parallel in, parallel out (buffered) | Serial in, parallel out | Data flow direction and format are incompatible, preventing direct substitution in most designs. |
| Supply Voltage Range | 2 V to 6 V | 2 V to 6 V | Both operate over the standard HC supply range, so voltage compatibility is not a differentiator. |
| Package | SO16 (D package) | SO16 (D package) | Same package footprint allows physical compatibility on a PCB, but electrical function still differs. |
| Propagation Delay (typical) | ~8 ns at 5 V | ~15 ns at 5 V (shift clock to output) | Timing differences affect maximum operating frequency and signal integrity in synchronous systems. |
| Output Drive Current | ±6 mA (standard HC) | ±6 mA (standard HC) | Similar drive capability means both can drive comparable loads, but functional differences remain decisive. |
| Primary Application | Bus buffering, signal driving, 3-state interfacing | Serial-to-parallel data conversion, LED/relay driving, I/O expansion | Intended use cases are distinct, so they serve different roles in a system and are not substitutes. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC594D | 74HC540D |
|---|---|---|
| Series | 74HC | 74HC |
| Part Status | Active | Active |
| Logic Type | Shift Register | Buffer, Inverting |
| Output Type | Push-Pull | 3-State |
| Number of Elements | 1 | 1 |
| Number of Bits per Element | 8 | 8 |
| Function | Serial to Parallel, Serial | - |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Operating Temperature | -40°C ~ 125°C | -40°C ~ 85°C (TA) |
| Mounting Type | Surface Mount | Surface Mount |
| Current - Output High Low | - | 7.8mA, 7.8mA |
Frequently asked questions
What are the primary functional differences between the 74HC540D and the 74HC594D?
The 74HC540D is an octal inverting buffer/line driver with 3-state outputs, designed for bus-oriented applications. The 74HC594D is an 8-bit serial-in/parallel-out shift register with an 8-bit output latch, used for serial-to-parallel data conversion and I/O expansion.
Are the 74HC540D and 74HC594D pin-compatible?
No. The 74HC540D is typically supplied in a 20-pin package (e.g., SO20), while the 74HC594D is typically supplied in a 16-pin package (e.g., SO16). They have different pin counts and pin functions, so they are not pin-compatible.
Can the 74HC540D and 74HC594D be used together in the same design?
Yes. They serve different functions and can be used together. For example, a 74HC594D can drive parallel data lines, and a 74HC540D can buffer or isolate those lines from a bus, provided the logic levels and supply voltages are compatible.
What are the output drive capabilities of the 74HC540D and 74HC594D?
Both devices are part of the 74HC family and typically provide standard CMOS output drive. The 74HC540D is specified with symmetrical output drive capable of driving bus lines, while the 74HC594D provides standard push-pull outputs for its parallel outputs. Exact drive currents should be verified from the respective manufacturer datasheets.
Do both the 74HC540D and 74HC594D operate at the same supply voltage range?
Yes. Both are 74HC series devices and typically operate over a supply voltage range of 2.0 V to 6.0 V. However, always confirm the specific operating range from the manufacturer datasheet for the exact part number and package.
Which device is better suited for serial-to-parallel data conversion?
The 74HC594D is specifically designed for serial-to-parallel data conversion because it contains an 8-bit shift register and an 8-bit output latch. The 74HC540D does not perform serial-to-parallel conversion; it is an octal buffer/line driver.
Can the 74HC540D be used to drive the inputs of the 74HC594D?
Yes, provided the logic levels and supply voltages are compatible. The 74HC540D can buffer or invert signals before they reach the 74HC594D inputs. Note that the 74HC540D is inverting, so the logic polarity must be considered in the design.
Are the 74HC540D and 74HC594D available in the same package types?
No. The 74HC540D is commonly available in 20-pin packages such as SO20, while the 74HC594D is commonly available in 16-pin packages such as SO16. Package options may vary by manufacturer, so verify the specific ordering code.