Part A
74HC574D
Toshiba Semiconductor and Storage
- Lifecycle
- Active
- Stock
- 3287 PCS
- Package
- SOIC-20
- Series
- Lógica - Flip Flops
Replacement verdict
Not a drop-in replacement
The 74HC574D and 74HC540D,652 are not functionally interchangeable despite sharing the 74HC logic family and similar SO package formats. The 74HC574D is an octal D-type flip-flop with three-state outputs that latches data on a clock edge, while the 74HC540D,652 is an octal inverting buffer/line driver with three-state outputs that responds combinationally to input changes. Their differing logic functions, output polarity, and control architectures make direct substitution impossible without redesigning the surrounding circuit.
Different logic function
Different output polarity
Different control architecture
Different timing behavior
Parts at a glance
Part B
74HC540D,652
NXP USA Inc.
- Lifecycle
- Active
- Stock
- 2550 PCS
- Package
- SOIC-20
- Series
- Lógica - Buffers, Drivers, Receivers, Transceivers
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 | 74HC540D,652 | Why it matters |
|---|---|---|---|
| Logic Function | Octal D-type flip-flop with 3-state outputs | Octal buffer/line driver with 3-state outputs | Determines the fundamental behavior; a flip-flop stores data on a clock edge, while a buffer only passes signals through, so they are not functionally interchangeable. |
| Number of Flip-Flops / Buffers | 8 | 8 | Both provide eight channels, so the channel count matches, but the internal function differs. |
| Output Type | 3-state, non-inverting | 3-state, inverting | Inverting versus non-inverting outputs changes the logic polarity, which affects signal integrity and requires design changes if substituted. |
| Clock Input | Yes (edge-triggered) | No | A clock input allows synchronous data capture; without it, the buffer cannot store or synchronize data. |
| Output Enable Control | Yes (OE) | Yes (OE1, OE2) | Both have output enable, but the 74HC540D,652 uses two enable pins for more flexible bus control. |
| Propagation Delay (typical) | ~20 ns at 4.5 V | ~12 ns at 4.5 V | Faster propagation delay improves timing margins in high-speed circuits. |
| Supply Voltage Range | 2 V to 6 V | 2 V to 6 V | Both support the same wide voltage range, allowing use in 3.3 V and 5 V systems. |
| Package | SOIC-20 | SOIC-20 | Identical package and pin count simplify PCB layout and assembly compatibility. |
| Operating Temperature Range | -40°C to +125°C | -40°C to +125°C | Same temperature range ensures both parts can be used in industrial and automotive environments. |
| Pin Count | 20 | 20 | Equal pin count means the same footprint, but pin functions differ, so direct drop-in replacement is not possible. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC574D | 74HC540D,652 |
|---|---|---|
| Supplier | - | Rochester Electronics, LLC |
| Series | 74HC | 74HC |
| Part Status | Active | Active |
| Logic Type | - | Buffer, Inverting |
| Number of Elements | 1 | 1 |
| Number of Bits per Element | 8 | 8 |
| Output Type | Tri-State, Non-Inverted | 3-State |
| Current - Output High Low | 7.8mA, 7.8mA | 7.8mA, 7.8mA |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Operating Temperature | -40°C ~ 85°C (TA) | -40°C ~ 125°C (TA) |
| Mounting Type | Surface Mount | Surface Mount |
| Function | Standard | - |
| Type | D-Type | - |
| Clock Frequency | 59 MHz | - |
| Max Propagation Delay @ V Max CL | 33ns @ 6V, 150pF | - |
| Trigger Type | Positive Edge | - |
| Current - Quiescent (Iq) | 4 µA | - |
| Input Capacitance | 5 pF | - |
Frequently asked questions
What are the primary functional differences between the 74HC574D and the 74HC540D,652?
The 74HC574D is an octal D-type flip-flop with 3-state outputs that captures data on the rising edge of the clock (CP) and presents it on the outputs. The 74HC540D,652 is an octal inverting buffer/line driver with 3-state outputs that provides non-clocked, inverting signal buffering controlled by two active-low output enable pins (OE1 and OE2).
Are the 74HC574D and 74HC540D,652 pin-to-pin compatible?
No. The 74HC574D uses a 20-pin package with a clock input (CP), eight D inputs, eight 3-state outputs, and a single output enable (OE). The 74HC540D,652 uses a 20-pin package with eight inputs, eight inverting 3-state outputs, and two active-low output enables (OE1 and OE2) but no clock pin. The pin functions and control logic differ, so they are not direct drop-in replacements.
Can the 74HC574D be used to replace the 74HC540D,652 in an existing design?
Not directly. The 74HC574D is edge-triggered and stores data, while the 74HC540D,652 is a combinational inverting buffer. Replacing one with the other requires redesigning the control logic, timing, and signal polarity, and verifying that the 3-state enable behavior and propagation delays meet the system requirements.
What are the output drive capabilities of the 74HC574D and 74HC540D,652?
Both devices are 74HC-series CMOS logic and typically provide symmetrical output drive specified as ±6 mA at 4.5 V and ±7.8 mA at 6 V per output, according to standard 74HC family datasheets. Actual drive strength should be confirmed on the specific manufacturer datasheet for the exact part number and package.
What is the difference in output polarity between the 74HC574D and the 74HC540D,652?
The 74HC574D provides non-inverting outputs: the logic level present at a D input when the clock rises appears at the corresponding Q output. The 74HC540D,652 provides inverting outputs: the logic level at each input appears inverted at the corresponding output when the device is enabled.
How do the 3-state output enable controls differ between the two devices?
The 74HC574D has a single active-low output enable (OE) that, when high, places all eight outputs in high-impedance state. The 74HC540D,652 has two active-low output enables (OE1 and OE2); both must be low to enable the outputs, and if either is high the outputs are in high-impedance state. This allows more flexible bus control in the 74HC540D,652.
Are the 74HC574D and 74HC540D,652 interchangeable in bus-oriented applications?
No, they serve different roles. The 74HC574D is typically used for registered data storage and synchronous bus driving, while the 74HC540D,652 is used for inverting buffering and line driving of combinational signals. Substitution requires matching the required function, timing, polarity, and enable logic to the system architecture.
What supply voltage range and logic family do the 74HC574D and 74HC540D,652 share?
Both are 74HC high-speed CMOS devices. The standard 74HC family operating supply voltage range is 2.0 V to 6.0 V, with typical operation at 5 V. Input thresholds and output levels are CMOS-compatible, and both devices are specified for operation over the standard 74HC temperature range. Verify exact limits on the manufacturer datasheet for the specific orderable part number.