74HCT245D vs 74HCT7403D,518

The 74HCT245D is an octal bus transceiver with 3-state outputs, designed for bidirectional asynchronous communication between data buses. The 74HCT7403D,518 is a quad 2-input NAND buffer with open-drain outputs, intended for logic gating and wired-OR applications. They serve fundamentally different logic functions and are not pin-to-pin or function-to-function equivalents.

No. The 74HCT245D is typically supplied in a 20-pin SOIC package, while the 74HCT7403D,518 is supplied in a 14-pin SOIC package. Pin counts, pin assignments, and package dimensions differ, so they cannot be interchanged on the same PCB footprint without redesign.

Yes. Both devices are members of the 74HCT logic family and are specified for a nominal supply voltage of 5 V, with a typical operating range of 4.5 V to 5.5 V. This allows them to be used in the same 5 V logic system, provided the functional and pinout differences are respected.

The 74HCT245D provides standard 3-state push-pull outputs with symmetrical source and sink current capability, typically ±6 mA per output. The 74HCT7403D,518 has open-drain outputs, which can sink current but cannot source current, and typically sink 4 mA. The open-drain configuration requires external pull-up resistors for logic-high output levels.

The 74HCT245D is the correct choice for bidirectional bus interfacing. It features an octal transceiver with direction control and output enable inputs, allowing data to flow in either direction between two buses. The 74HCT7403D,518 is a unidirectional logic gate and cannot perform bus transceiver functions.

No. The 74HCT245D supports 3-state outputs, enabling high-impedance isolation from the bus when disabled. The 74HCT7403D,518 has open-drain outputs, which are not 3-state; when the output transistor is off, the output is pulled high by an external resistor rather than entering a high-impedance state.

For the 74HCT245D, the typical propagation delay from A to B or B to A is approximately 12 ns at 5 V. For the 74HCT7403D,518, the typical propagation delay from input to output is approximately 15 ns at 5 V. Exact values depend on load conditions and should be verified from the respective manufacturer datasheets.

No. The two devices differ in logic function, pin count, package, output type, and control signals. The 74HCT7403D,518 cannot perform bidirectional bus transceiver operations, lacks 3-state outputs, and has a different pinout. Direct replacement is not possible without significant circuit redesign.