Part A
74HC573D
Toshiba Halbleiter und Speicher
- Lifecycle
- Active
- Stock
- 3424 Stückzahl
- Package
- SOIC-14
- Series
- Logic-Verriegelungen
Replacement verdict
Not a drop-in replacement
The 74HC540D and 74HC573D are not functionally interchangeable despite sharing the same 74HC logic family and DIP-20/SOIC-20 package footprint. The 74HC540D is an inverting octal buffer/line driver with 3-state outputs intended for bus driving, while the 74HC573D is a transparent octal D-type latch with 3-state outputs intended for data storage and bus interfacing. Their internal logic functions, pin functions, and control signal behavior differ fundamentally, so direct substitution is not possible without circuit redesign.
Different logic function
Different output polarity
Different control signals
Different pin functions
Parts at a glance
Part B
74HC540D
Toshiba Halbleiter und Speicher
- Lifecycle
- Active
- Stock
- 5312 Stückzahl
- Package
- SOIC-20
- Series
- Logic c Puffer, Treiber, Empfänger, Transceiver
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 | 74HC573D | Why it matters |
|---|---|---|---|
| Logic Function | Octal buffer/line driver with 3-state outputs, inverting | Octal D-type transparent latch with 3-state outputs | Defines the core function; a buffer drives signals while a latch stores data, so they are not functionally interchangeable. |
| Output Type | Inverting | Non-inverting | Inverted versus non-inverted outputs change the logic polarity seen by downstream circuits. |
| Data Storage | None (combinational buffer) | Transparent D-type latch | A latch can hold data between clock edges, while a buffer cannot, affecting timing and circuit architecture. |
| Control Inputs | Output enable (OE1, OE2) | Latch enable (LE) and output enable (OE) | Different control pins determine how the device is enabled and when data is captured or driven. |
| Number of Channels | 8 | 8 | Matching channel count allows similar bus width handling in a design. |
| Supply Voltage Range | 2 V to 6 V | 2 V to 6 V | Compatible supply range ensures both parts can operate in the same logic-level environment. |
| Output Drive Current | ±6 mA (typical at 4.5 V) | ±6 mA (typical at 4.5 V) | Similar drive strength affects fan-out and ability to drive loads or transmission lines. |
| Package | SO16 (SOIC-16) | SO16 (SOIC-16) | Identical package footprint allows the same PCB layout to accommodate either device. |
| Pin Count | 16 | 16 | Same pin count is necessary for physical compatibility in a shared socket or footprint. |
| Propagation Delay | ~8 ns (typical at 4.5 V) | ~14 ns (typical at 4.5 V) | Different delays affect timing margins and maximum operating frequency in synchronous designs. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC573D | 74HC540D |
|---|---|---|
| Series | 74HC | 74HC |
| Part Status | Active | Active |
| Logic Type | D-Type Latch | Buffer, Inverting |
| Circuit | 8:8 | - |
| Output Type | Tri-State | 3-State |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Independent Circuits | 1 | - |
| Delay Time - Propagation | 26ns | - |
| Current - Output High Low | 7.8mA, 7.8mA | 7.8mA, 7.8mA |
| Operating Temperature | -40°C ~ 85°C | -40°C ~ 85°C (TA) |
| Mounting Type | Surface Mount | Surface Mount |
| Number of Elements | - | 1 |
| Number of Bits per Element | - | 8 |
Frequently asked questions
What are the primary functional differences between the 74HC540D and the 74HC573D?
The 74HC540D is an octal inverting buffer/line driver with 3-state outputs, featuring two active-low output enable pins that control four outputs each. The 74HC573D is an octal D-type transparent latch with 3-state outputs, featuring a latch enable (LE) pin and a single active-low output enable (OE) pin. The 74HC540D provides signal buffering and inversion without storage, while the 74HC573D can capture and hold data, making it suitable for data bus interfacing and temporary storage applications.
Are the 74HC540D and 74HC573D pin-compatible?
No. Although both devices are typically offered in a 20-pin package such as SOIC-20 or TSSOP-20, their pin functions differ. The 74HC540D uses pins 1 and 19 as active-low output enable inputs (OE1 and OE2), with pin 10 as GND and pin 20 as VCC. The 74HC573D uses pin 1 as the output enable (OE), pin 11 as the latch enable (LE), pin 10 as GND, and pin 20 as VCC. Because the control pin assignments and internal signal paths differ, they are not direct drop-in replacements.
Can the 74HC540D and 74HC573D be used interchangeably in a design?
No, they cannot be used interchangeably without design changes. The 74HC540D inverts the input signal and has no data storage capability, while the 74HC573D provides non-inverting transparent latching. A circuit designed for one device would require logic and timing modifications to function correctly with the other. The output enable control schemes also differ: the 74HC540D has two active-low enables, whereas the 74HC573D has one active-low enable plus a latch enable input.
What are the typical operating voltage and logic family specifications for both devices?
Both the 74HC540D and 74HC573D belong to the 74HC high-speed CMOS logic family. They typically operate over a supply voltage range of 2.0 V to 6.0 V, with characterized performance at 4.5 V and 6.0 V. Input thresholds and output drive characteristics are consistent with standard 74HC specifications. These parameters should be verified against the specific manufacturer datasheet, as minor variations may exist between suppliers.
What is the difference in output drive capability between the 74HC540D and 74HC573D?
Both devices are specified with standard 74HC output drive, typically capable of driving 15 LSTTL loads or providing ±4 mA output current at 4.5 V and ±5.2 mA at 6.0 V per output. The 74HC540D is often characterized as a line driver with symmetrical output drive, while the 74HC573D provides similar drive strength for bus-oriented applications. Exact drive current ratings should be confirmed from the manufacturer datasheet for the specific part number and package.
Which device is more suitable for bus-oriented applications?
The 74HC573D is generally more suitable for bus-oriented applications because it includes a transparent D-type latch that can hold data while the bus is used for other purposes. The 74HC573D also features a single output enable pin that places all eight outputs in high-impedance state, which is convenient for bus sharing. The 74HC540D is better suited for pure buffering, driving, and inverting applications where data storage is not required.
Do both devices feature 3-state outputs?
Yes, both the 74HC540D and 74HC573D feature 3-state outputs. When the output enable conditions are met, the outputs are placed in a high-impedance state, allowing multiple devices to share a common bus. On the 74HC540D, two active-low enable pins control the high-impedance state in two groups of four outputs. On the 74HC573D, a single active-low output enable pin controls all eight outputs simultaneously.
What are the typical propagation delay characteristics of these devices?
Both devices are 74HC-family CMOS logic and typically exhibit propagation delays in the range of approximately 10 ns to 20 ns at 4.5 V supply, depending on load conditions and manufacturer. The 74HC540D propagation delay is specified from input to output, while the 74HC573D has separate specifications for data-to-output and latch-enable-to-output paths. For accurate timing analysis, the specific manufacturer datasheet and operating conditions must be consulted.