Overview
The SN74HC245PWG4, produced by Texas Instruments, is an octal bus transceiver with 3-state outputs. This device is designed for asynchronous two-way communication between data buses, making it versatile for various digital logic applications. The SN74HC245PWG4 allows data transmission from the A bus to the B bus or from the B bus to the A bus, depending on the logic level at the direction-control (DIR) input. The output-enable (OE) input can be used to disable the device, effectively isolating the buses.
Key Specifications
| Parameter | Min | Typ | Max | Unit |
|---|---|---|---|---|
| VCC Supply Voltage | 2 | 5 | 6 | V |
| VIH High-Level Input Voltage (VCC = 2 V) | 1.5 | 1.5 | V | |
| VIH High-Level Input Voltage (VCC = 4.5 V) | 3.15 | 3.15 | V | |
| VIH High-Level Input Voltage (VCC = 6 V) | 4.2 | 4.2 | V | |
| VIL Low-Level Input Voltage (VCC = 2 V) | 0.5 | 0.5 | V | |
| VIL Low-Level Input Voltage (VCC = 4.5 V) | 1.35 | 1.35 | V | |
| VIL Low-Level Input Voltage (VCC = 6 V) | 1.8 | 1.8 | V | |
| TA Operating Free-Air Temperature | -40 | 85 | °C | |
| tpd Propagation Delay (A or B to A or B) at VCC = 5 V, CL = 50 pF | 15 | 21 | 32 | ns |
| IOH High-Level Output Current | -20 | µA | ||
| IO Continuous Output Current | ±35 | mA |
Key Features
- Wide operating voltage range from 2 V to 6 V.
- High-current 3-state outputs capable of driving bus lines directly or up to 15 LSTTL loads.
- Control-function implementation minimizes external timing requirements.
- Data transmission from the A bus to the B bus or from the B bus to the A bus, controlled by the DIR input.
- Output-enable (OE) input to disable the device and isolate the buses.
- Low drive and slow edge rates to minimize output ringing, overshoot, and undershoot.
Applications
The SN74HC245PWG4 is suitable for a variety of bus interface applications where output ringing is a concern. It can be used in systems requiring asynchronous two-way communication between data buses, such as:
- Microcontroller and peripheral interfaces.
- Data transmission between different voltage domains.
- Bus isolation and control in digital systems.
- Applications involving LEDs, relays, or other system boards.
Q & A
- What is the operating voltage range of the SN74HC245PWG4?
The operating voltage range is from 2 V to 6 V.
- How does the direction-control (DIR) input function?
The DIR input controls the direction of data transmission between the A and B buses.
- What is the purpose of the output-enable (OE) input?
The OE input can be used to disable the device, effectively isolating the buses.
- What are the propagation delay times for this device?
The propagation delay times vary depending on VCC and load capacitance, but for VCC = 5 V and CL = 50 pF, it ranges from 15 ns to 32 ns.
- How should unused inputs be handled?
Unused inputs must be held at VCC or GND to ensure proper device operation.
- What are the thermal characteristics of the device?
The junction-to-ambient thermal resistance varies by package, e.g., 92.1 °C/W for the DB (SSOP) package.
- What are the recommended power supply bypass capacitor values?
A 0.1 μF capacitor is recommended for single supply devices, and 0.01 μF or 0.022 μF for each power pin in multiple VCC pin configurations.
- Can the SN74HC245PWG4 drive high loads?
The device can drive up to 15 LSTTL loads and has high-current 3-state outputs.
- How should the layout be designed for this device?
Inputs should never float, and good bypass capacitors should be placed close to the power pins to prevent power disturbances.
- What are some typical applications of the SN74HC245PWG4?
It is used in microcontroller and peripheral interfaces, data transmission between different voltage domains, and bus isolation and control in digital systems.
