Part A
74HC595D
Toshiba Semiconductor et stockage
- Lifecycle
- Active
- Stock
- 4369 PCS
- Package
- SOIC-16
- Series
- Logique - Registre à décalage
Replacement verdict
Not a drop-in replacement
The 74HC595D and 74HC540D,652 are functionally unrelated ICs and cannot serve as substitutes for one another. The 74HC595D is an 8-bit serial-in/parallel-out shift register with output latches and tri-state outputs, while the 74HC540D,652 is an 8-bit inverting octal buffer/line driver with tri-state outputs. Their internal logic, pin functions, and intended applications differ fundamentally, so direct replacement is not feasible in any design.
Different logic function
Different input type
Different output type
Different pinout
Parts at a glance
Part B
74HC540D,652
NXP USA Inc.
- Lifecycle
- Active
- Stock
- 2550 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 | 74HC595D | 74HC540D,652 | Why it matters |
|---|---|---|---|
| Logic Function | 8-bit serial-in/parallel-out shift register with output latches | Octal inverting buffer/line driver with 3-state outputs | The core function determines whether the device can serialize data (shift register) or only buffer/invert signals, making them non-substitutable for each other's primary role. |
| Output Type | Parallel, 3-state (registered) | 3-state, inverting | Output configuration affects how the device drives loads and whether it can share a bus; the 595 has latched parallel outputs while the 540 provides inverting 3-state outputs. |
| Number of Outputs | 8 | 8 | Both provide 8 outputs, so channel count alone does not differentiate them, but the output behavior differs. |
| Input Type | Serial (with shift register clock and latch clock) | Parallel | Input architecture dictates the data loading method; the 595 accepts serial data while the 540 accepts parallel inputs. |
| Propagation Delay (typical) | ~14 ns at 5 V (shift clock to output) | ~8 ns at 5 V (input to output) | Speed affects timing margins in high-frequency designs; the 540 is generally faster for direct buffering applications. |
| Supply Voltage Range | 2 V to 6 V | 2 V to 6 V | Both operate over the standard HC-family voltage range, so supply compatibility is equivalent. |
| Output Current (per pin) | ±6 mA (typical at 5 V) | ±6 mA (typical at 5 V) | Drive strength is similar, but the 540 is often used for bus driving while the 595 drives latched outputs. |
| Package | SO16 (D package) | SO20 (D package) | Different pin counts and footprints prevent direct drop-in replacement without layout changes. |
| Operating Temperature Range | -40 °C to +125 °C | -40 °C to +125 °C | Both support industrial temperature ranges, so environmental compatibility is equivalent. |
| Latch/Register Feature | Yes (output latch register) | No | The 595 can hold output states independently of the shift register, enabling stable parallel output; the 540 has no storage element. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC595D | 74HC540D,652 |
|---|---|---|
| Supplier | - | Rochester Electronics, LLC |
| Series | 74HC | 74HC |
| Part Status | Active | Active |
| Logic Type | Shift Register | Buffer, Inverting |
| Number of Elements | 1 | 1 |
| Number of Bits per Element | 8 | 8 |
| Output Type | Tri-State | 3-State |
| Current - Output High Low | - | 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 |
| Function | Serial to Parallel, Serial | - |
Frequently asked questions
What are the primary functional differences between the 74HC595D and the 74HC540D,652?
The 74HC595D is an 8-bit serial-in, parallel-out shift register with a storage register and 3-state output registers, used to expand GPIO. The 74HC540D,652 is an 8-bit inverting 3-state buffer/line driver with Schmitt-trigger inputs, used for signal buffering and driving. They are not functionally interchangeable.
Are the 74HC595D and 74HC540D,652 pin-compatible?
No. The 74HC595D uses a 16-pin SO package with serial data, shift clock, latch clock, output enable, and serial output pins. The 74HC540D,652 uses a 20-pin SO package with eight inputs, eight inverted outputs, and two output-enable pins. Pin counts and pin functions differ.
Can the 74HC595D directly replace the 74HC540D,652 in an existing design?
No. The 74HC595D is a serial-to-parallel shift register, while the 74HC540D,652 is an inverting octal buffer. Their logic functions, pinouts, and package sizes are different, so a direct replacement is not possible without redesigning the circuit.
What are the output drive capabilities of the 74HC595D and 74HC540D,652?
Both devices are HC-family CMOS parts. The 74HC595D provides standard CMOS outputs suitable for low-power logic interfacing. The 74HC540D,652 is specified as a line driver/buffer with higher output drive intended for bus or line driving. Exact current ratings should be verified from the respective manufacturer datasheets.
Do both devices operate at the same supply voltage range?
Yes. Both the 74HC595D and 74HC540D,652 are 74HC-series devices and typically operate from 2.0 V to 6.0 V. Verify the exact recommended operating conditions in the manufacturer datasheet for the specific part number and package.
Which device is better for expanding microcontroller output pins?
The 74HC595D is intended for output expansion because it converts serial data into eight parallel outputs using only three control lines. The 74HC540D,652 does not perform serial-to-parallel conversion and is used for buffering or inverting existing parallel signals.
Are the logic input thresholds and Schmitt-trigger characteristics the same?
No. The 74HC540D,652 includes Schmitt-trigger inputs, which provide hysteresis for slow or noisy input signals. The 74HC595D uses standard CMOS input structures without specified Schmitt-trigger hysteresis. Input threshold behavior should be confirmed from the respective datasheets.
What package options are relevant for the 74HC595D and 74HC540D,652?
The 74HC595D is commonly supplied in a 16-pin SO package. The 74HC540D,652 is commonly supplied in a 20-pin SO package. Package footprint, pin count, and thermal characteristics differ, so PCB layout changes are required when switching between them.