74HCT245 Bus Transceiver with 3-State Outputs

Description

The 74HCT245 Bus Transceiver with 3-state outputs is very useful in solving a number of logic interfacing challenges.

PACKAGE INCLUDES:

• 74HCT245 Bus Transceiver with 3-State outputs (DIP Package)

KEY FEATURES OF 74HCT245 BUS TRANSCEIVER:

• 8 Bi-directional channels with direction and 3-state output control
• Accepts 3.3V or 5V logic inputs and provides 5V logic outputs
• Up to ±35mA sink / source capability
• 5V operation

Here are a couple of the more common applications for using the 74HCT245.

Providing 3.3V to 5V Logic Level Conversion

In many cases, 3.3V devices can directly drive 5V devices because the logic high of around 3V on the output of the 3.3V device is high enough to be seen as a logic high on the input of the 5V device.

In some cases though, the 5V device requires a higher input voltage for a valid logic high to be reliably detected.  Addressable RGB LEDs like the WS2812 often need a logic signal near 5V to work correctly and these chips are handy for making that translation.  Another example is the common MAX7219 LED display driver that requires a minimum of 3.5V for a valid logic high on its inputs.  The 74HCT245 can accept down to 2V for a logic high on its input and will provide a minimum of 4.4V logic high on its output.

These logic devices can operate at much higher frequencies than the common MOSFET level shifters when working with fast signals like SPI.

Providing Buffered 5V Outputs

Some MCUs struggle with providing enough drive current on their output pins.  The74HCT245 can sink or source up to 35mA per output.  If using to drive heavy loads, keep in mind that the total package current should be kept under 75mA to avoid thermal issues.

Providing 3-State and Directional Control on 5V Logic Signals

Devices sometimes behave badly and drive their pins when they shouldn’t. This is a common problem with modules that use the SPI bus. The 3-state outputs can be used to enable / disable incoming signals based on the MCUs requirements.  The  Output Enable controls all 8 channels.  If individual channel control is needed, the 74HCT125 may be a better fit.

In some cases, the same pins on an MCU need to be used alternatively as inputs or outputs.  The directional control pin on the 74HCT245 can be used to change the direction of data flow through the device.

Notes: 

1. None

Technical Specifications