Part A
74HC574D
Компания Toshiba Semiconductor и Storage
- Lifecycle
- Active
- Stock
- 3287 ПКС
- Package
- SOIC-20
- Series
- Логика - Flip Flops
Replacement verdict
Not a drop-in replacement
The 74HC540D and 74HC574D are not functionally interchangeable despite sharing the same 74HC CMOS logic family and DIP-20/SO-20 package footprint. The 74HC540D is an inverting octal buffer/line driver with 3-state outputs controlled by two active-low output enable pins, while the 74HC574D is an octal D-type flip-flop with 3-state outputs that latches data on a positive clock edge. Their internal logic functions, control pin assignments, and signal timing behavior are fundamentally different, so neither device can directly substitute for the other in an existing design without circuit redesign.
Different logic function
Different control interface
Different timing behavior
Different pin function mapping
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 | 74HC574D | Why it matters |
|---|---|---|---|
| Logic Function | Octal buffer/line driver with 3-state outputs, inverting | Octal D-type flip-flop with 3-state outputs, positive edge triggered | Defines the core behavior; a buffer passes signals combinationally while a flip-flop latches data on a clock edge, so they are not functionally interchangeable. |
| Output Type | 3-state, inverting | 3-state, non-inverting | Inverting versus non-inverting outputs change the logic polarity seen by downstream circuitry. |
| Clock Input | None | Yes (CP, positive edge triggered) | A clocked device stores data synchronously, whereas an unclocked buffer responds immediately to input changes. |
| Number of Output Enable Controls | 2 (active-low OE1, OE2) | 1 (active-low OE) | Different enable configurations affect how the outputs can be gated or multiplexed in a bus system. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | Both operate over the standard HC-family supply range, so power supply compatibility is identical. |
| Number of Channels | 8 | 8 | Matching channel count means both can handle the same bus width. |
| Package | SO16 (SOIC-16) | SO16 (SOIC-16) | Identical package and pin count allow the same PCB footprint, though pin functions differ. |
| Logic Family | 74HC | 74HC | Same logic family ensures compatible input thresholds and output drive characteristics. |
| Propagation Delay (typical) | Approximately 8 ns at 5 V | Approximately 14 ns at 5 V (clock to output) | Timing differences affect maximum operating frequency and setup/hold requirements in synchronous designs. |
Need help validating a replacement?
Send your BOM and application constraints for technical and sourcing review.
Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC574D | 74HC540D |
|---|---|---|
| Series | 74HC | 74HC |
| Part Status | Active | Active |
| Function | Standard | - |
| Type | D-Type | - |
| Output Type | Tri-State, Non-Inverted | 3-State |
| Number of Elements | 1 | 1 |
| Number of Bits per Element | 8 | 8 |
| 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 | 7.8mA, 7.8mA |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Current - Quiescent (Iq) | 4 µA | - |
| Input Capacitance | 5 pF | - |
| Operating Temperature | -40°C ~ 85°C (TA) | -40°C ~ 85°C (TA) |
| Mounting Type | Surface Mount | Surface Mount |
| Logic Type | - | Buffer, Inverting |
Frequently asked questions
What are the primary functional differences between the 74HC540D and the 74HC574D?
The 74HC540D is an octal inverting buffer/line driver with 3-state outputs, featuring two active-low output enable pins (OE1 and OE2). The 74HC574D is an octal D-type flip-flop with 3-state outputs, featuring a clock input (CP) and an output enable pin (OE). The 74HC540D is combinational logic, while the 74HC574D is sequential logic with edge-triggered storage.
Are the 74HC540D and 74HC574D pin-to-pin compatible?
No. Although both are typically offered in a 20-pin SOIC package (D suffix), their pin functions differ. The 74HC540D has two output enable pins and no clock, while the 74HC574D has a clock input and a single output enable. Pin assignments for control signals and data flow are not identical, so they cannot be interchanged without circuit redesign.
Can the 74HC540D and 74HC574D be used in the same application interchangeably?
No. The 74HC540D provides real-time inverting buffering of input signals, whereas the 74HC574D latches data on a clock edge and holds it. Substitution would require changes to the control logic and timing, and would alter the circuit's functionality from combinational to sequential.
What are the output drive capabilities of the 74HC540D and 74HC574D?
Both devices are 74HC series CMOS logic and typically provide symmetrical output drive of ±4 mA at 5 V VCC (standard 74HC family). However, actual drive strength should be verified from the specific manufacturer datasheet, as some variants may differ. Both feature 3-state outputs for bus-oriented applications.
Do both the 74HC540D and 74HC574D have 3-state outputs?
Yes. Both the 74HC540D and 74HC574D feature 3-state outputs, allowing them to be connected to a shared bus. The 74HC540D places outputs in high-impedance state when either OE1 or OE2 is high. The 74HC574D places outputs in high-impedance state when OE is high, independent of the clock.
What is the difference in propagation delay between the 74HC540D and 74HC574D?
The 74HC540D propagation delay (tPD) is typically in the range of 8–15 ns at 5 V VCC, depending on load and manufacturer. The 74HC574D has a similar propagation delay from clock to output, but also requires setup and hold times for the D inputs relative to the clock edge. Exact values must be taken from the specific manufacturer datasheet.
Which device is better for bus driving applications, the 74HC540D or 74HC574D?
Both are suitable for bus driving due to their 3-state outputs. The 74HC540D is used for inverting buffering of bus signals without storage. The 74HC574D is used when data must be captured and held on a clock edge before being placed on the bus. The choice depends on whether registered (sequential) or non-registered (combinational) behavior is required.
Are the 74HC540D and 74HC574D available in the same package options?
Both are commonly available in a 20-pin SOIC package with the D suffix (e.g., 74HC540D, 74HC574D). They may also be offered in other packages such as TSSOP or DIP by various manufacturers. Package availability should be confirmed with the specific manufacturer or distributor.