The 74HCT125 4-Ch buffer with 3-state outputs is very useful in solving a number of logic interfacing challenges.
- CD74HC125E 4-Ch Buffer with 3-State outputs (DIP Package)
KEY FEATURES OF 74HC595 8-BIT SHIFT REGISTER:
- 4-channels each with independent 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 74HCT125.
Providing 3-State Control on 5V Logic Signals
Devices sometimes behave badly and drive their pins when they shouldn’t. This is a fairly common problem with some SPI bus implementations where a module drives the SPI bus even when the part is not selected.
If there are other devices on the SPI bus, this can create a conflict. The 74HCT125 allows the MCU to control when the outputs are enabled by toggling the output enable on the individual channels.
The device is also fast and can operate at typical SPI bus speeds where the common MOSFET level shifters are too slow for reliable operation.
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. The common MAX7219 LED display driver for instance requires a minimum of 3.5V for a valid logic high on its inputs. The 74HCT125 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.
Providing Buffered Outputs
Some MCUs struggle with providing enough drive current on their output pins. The74HCT125 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 70mA to avoid thermal issues.
- Any unused inputs should be tied to Vcc or Gnd either directly or through a pull-up / pull-down resistor.
|Operating Voltage Range||4.5 – 5.5V|
|Continuous output current||Maximum||±35mA|
|Continuous package current||Maximum||±70mA|
|High level input voltage||Minimum||2V|
|High level output voltage||Typical||4.4V|
|Low level input voltage||Maximum||0.8V|
|Low level output voltage||Typical||0.26V|
|Package Type||Plastic, thru-hole DIP-16|