How to Use SN74AHCT125N: Examples, Pinouts, and Specs

The SN74AHCT125N is a quad buffer/driver with 3-state outputs, designed for high-speed operation and low power consumption. It is part of the Advanced High-Speed CMOS (AHCT) logic family and is widely used in digital circuits for signal buffering, level shifting, and driving loads. Each of the four independent buffers features a 3-state output, which can be enabled or disabled via a control input, making it ideal for bus-oriented applications.

• Signal buffering in digital circuits
• Level shifting between different voltage domains
• Driving high-capacitance loads
• Bus interface and control in microcontroller or microprocessor systems

• Supply Voltage (Vcc): 4.5V to 5.5V
• Input Voltage Range: 0V to 5.5V
• Output Voltage Range: 0V to Vcc
• High-Level Output Current (IOH): -8mA
• Low-Level Output Current (IOL): 8mA
• Propagation Delay (tpd): 4.5ns (typical at 5V)
• Power Consumption: Low power CMOS design
• Operating Temperature Range: -40°C to 85°C
• Package Type: 14-pin PDIP (Plastic Dual In-line Package)

The SN74AHCT125N has 14 pins, as described in the table below:

1. Power Supply: Connect the Vcc pin (Pin 14) to a 5V power supply and the GND pin (Pin 7) to ground.
2. Input Signals: Provide the input signals to the A pins (Pins 2, 5, 9, and 12) for the respective buffers.
3. Output Enable Control: Use the OE pins (Pins 1, 4, 10, and 13) to enable or disable the outputs. When the OE pin is LOW, the corresponding output is active. When the OE pin is HIGH, the output is in a high-impedance (Hi-Z) state.
4. Output Signals: The buffered output signals are available on the Y pins (Pins 3, 6, 8, and 11).

• Ensure that the supply voltage (Vcc) is within the specified range (4.5V to 5.5V) to avoid damage to the component.
• Use decoupling capacitors (e.g., 0.1µF) close to the Vcc pin to stabilize the power supply and reduce noise.
• Avoid leaving unused inputs floating; connect them to either Vcc or GND to prevent unpredictable behavior.
• When using the 3-state outputs, ensure proper control of the OE pins to avoid bus contention.

The SN74AHCT125N can be used with an Arduino UNO to buffer signals or interface with other devices. Below is an example of how to use it to buffer a digital signal:

• Connect the Vcc pin (Pin 14) to the Arduino's 5V pin.
• Connect the GND pin (Pin 7) to the Arduino's GND pin.
• Connect an Arduino digital output pin (e.g., Pin 8) to the 1A pin (Pin 2) of the SN74AHCT125N.
• Connect the 1OE pin (Pin 1) to GND to enable the output.
• Connect the 1Y pin (Pin 3) to the input of the device you want to drive.

// Example code to demonstrate using the SN74AHCT125N with an Arduino UNO

void setup() {
  pinMode(8, OUTPUT); // Set Arduino Pin 8 as an output
}

void loop() {
  digitalWrite(8, HIGH); // Send a HIGH signal to the SN74AHCT125N input
  delay(1000);           // Wait for 1 second
  digitalWrite(8, LOW);  // Send a LOW signal to the SN74AHCT125N input
  delay(1000);           // Wait for 1 second
}

1. No Output Signal:

   • Ensure the OE pin for the corresponding buffer is connected to GND (active LOW).
   • Verify that the input signal is correctly applied to the A pin.

2. Unstable or Noisy Output:

   • Check the power supply and ensure proper decoupling capacitors are used.
   • Verify that unused inputs are not left floating; tie them to Vcc or GND.

3. High-Impedance Output When Not Expected:

   • Confirm that the OE pin is not accidentally set to HIGH, which disables the output.

4. Component Overheating:

   • Ensure the output current does not exceed the specified limits (-8mA for HIGH, 8mA for LOW).
   • Verify that the supply voltage is within the recommended range.

Q: Can the SN74AHCT125N be used for level shifting?
A: Yes, the SN74AHCT125N can be used for level shifting from 3.3V logic to 5V logic, as it is designed to accept 3.3V inputs while operating at a 5V supply.

Q: What happens if the OE pin is left floating?
A: Leaving the OE pin floating can result in unpredictable behavior. Always connect it to either GND (to enable the output) or Vcc (to disable the output).

Q: Can the SN74AHCT125N drive multiple devices?
A: Yes, but ensure the total load does not exceed the maximum output current rating of the device. Use additional buffers if necessary.