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 74HC574D and 74HC595D are not functionally interchangeable despite sharing the same 74HC logic family and SOIC-16 package. The 74HC574D is an octal D-type flip-flop with 3-state outputs intended for parallel data storage, while the 74HC595D is an 8-bit serial-in/parallel-out shift register with an integrated output latch and 3-state outputs intended for serial-to-parallel conversion. Their internal architectures, pin functions, and control signal sets differ fundamentally, so neither device can directly substitute for the other in an existing design without significant circuit redesign.
Different logic function
Different pin functions
Different control interface
Different data flow direction
Parts at a glance
Part B
74HC574D
Toshiba Semiconductor et stockage
- Lifecycle
- Active
- Stock
- 3287 PCS
- Package
- SOIC-20
- Series
- Logique - Triggers
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HC574D | 74HC595D | Why it matters |
|---|---|---|---|
| Logic Function | Octal D-type flip-flop, 3-state | 8-bit serial-in/serial or parallel-out shift register with output latches, 3-state | Defines the fundamental behavior; these devices are not functionally interchangeable as they perform different logic operations. |
| Number of Outputs | 8 (parallel) | 8 (parallel) plus serial output | The 74HC595D provides an additional serial output for cascading, which the 74HC574D lacks. |
| Data Input Type | Parallel (8-bit) | Serial (1-bit) | Determines how data is loaded; parallel loading is faster for wide data, while serial loading reduces pin count. |
| Output Type | 3-state | 3-state | Both feature 3-state outputs, allowing connection to a shared bus, but the control logic differs. |
| Latch/Register Stages | Single register (flip-flop) | Two stages: shift register and output latch | The 74HC595D can hold output data stable while shifting new data, enabling glitch-free updates; the 74HC574D updates outputs directly on clock edge. |
| Package | SOIC-20 (D suffix) | SOIC-16 (D suffix) | Different pin counts and footprints prevent direct PCB drop-in replacement. |
| Pin Count | 20 | 16 | Pin count affects board layout and available I/O; they are not pin-compatible. |
| Supply Voltage Range | 2 V to 6 V | 2 V to 6 V | Both operate over the standard HC family voltage range, so power supply compatibility is maintained. |
| Propagation Delay (typical at 5 V) | ~20 ns | ~20 ns (shift) / ~20 ns (latch) | Similar speed performance, but the 74HC595D has additional delay through two stages. |
| Maximum Clock Frequency | ~50 MHz | ~50 MHz | Both can operate at similar clock rates, but the 74HC595D requires more clock cycles to load data serially. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC595D | 74HC574D |
|---|---|---|
| Series | 74HC | 74HC |
| Part Status | Active | Active |
| Logic Type | Shift Register | - |
| Output Type | Tri-State | Tri-State, Non-Inverted |
| Number of Elements | 1 | 1 |
| Number of Bits per Element | 8 | 8 |
| Function | Serial to Parallel, Serial | Standard |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Operating Temperature | -40°C ~ 125°C | -40°C ~ 85°C (TA) |
| Mounting Type | Surface Mount | Surface Mount |
| Type | - | D-Type |
| Clock Frequency | - | 59 MHz |
| Max Propagation Delay @ V Max CL | - | 33ns @ 6V, 150pF |
| Trigger Type | - | Positive Edge |
| Current - Output High Low | - | 7.8mA, 7.8mA |
| Current - Quiescent (Iq) | - | 4 µA |
| Input Capacitance | - | 5 pF |
Frequently asked questions
What is the fundamental functional difference between the 74HC574D and the 74HC595D?
The 74HC574D is an octal D-type flip-flop with 3-state outputs, used for parallel data storage and buffering. The 74HC595D is an 8-bit serial-in, parallel-out shift register with a storage register and 3-state outputs, used for serial-to-parallel data conversion.
Can the 74HC574D and 74HC595D be used interchangeably in a design?
No. They have different internal architectures and pin functions. The 74HC574D provides parallel D-type inputs and parallel 3-state outputs, while the 74HC595D provides a serial input, shift register, storage register, and parallel 3-state outputs. Direct substitution is not possible without redesigning the data interface.
How many pins do the 74HC574D and 74HC595D have, and are they pin-compatible?
Both devices are typically offered in a 16-pin package (e.g., SOIC-16). However, they are not pin-compatible because the pin functions differ. For example, the 74HC574D has eight parallel data inputs (D0–D7), while the 74HC595D uses pins for serial input (DS), shift clock (SHCP), storage clock (STCP), and output enable (OE), among others.
What are the typical output drive capabilities of the 74HC574D and 74HC595D?
Both are 74HC-series CMOS devices and typically provide standard CMOS output drive. Verified datasheets from manufacturers such as Nexperia, Texas Instruments, or ON Semiconductor specify output current per pin (e.g., ±4 mA or ±6 mA at specified VCC) and absolute maximum ratings. Designers must consult the specific manufacturer datasheet for exact drive strength and derating information.
Which device is better suited for expanding the number of output pins on a microcontroller?
The 74HC595D is generally preferred for output pin expansion because it requires only three control lines (serial data, shift clock, storage clock) and can be cascaded to drive many outputs. The 74HC574D requires a parallel data bus and address decoding, consuming more I/O pins on the host controller.
Do both the 74HC574D and 74HC595D have 3-state outputs?
Yes. Both devices feature 3-state outputs that can be placed in a high-impedance state via an output enable (OE) control pin. This allows the outputs to be connected to a shared bus without contention when disabled.
What are the typical operating voltage and temperature ranges for the 74HC574D and 74HC595D?
Both are 74HC-series high-speed CMOS devices. Standard specifications include an operating supply voltage range of 2.0 V to 6.0 V and an ambient operating temperature range of –40 °C to +125 °C for many industrial-grade versions. Always verify the exact ratings from the specific manufacturer datasheet, as ranges can vary by part variant and package.
Can the 74HC595D be used to drive LEDs directly, and how does this compare to the 74HC574D?
Both devices can sink or source limited current per output as specified in their datasheets. The 74HC595D is commonly used for LED driving because its serial interface reduces pin count and allows cascading. The 74HC574D can also drive LEDs but requires a parallel data source. In both cases, total package power dissipation and per-pin current limits must be respected, and external drivers may be required for high-current LEDs.