74HC573D vs 74HC540D

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.

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.

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.

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.

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.

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.

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.

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.