How to Use ADG728 Matrix Switch: Examples, Pinouts, and Specs

The ADG728 is a dual 4-channel analog switch manufactured by Adafruit. It is designed for switching multiple analog signals in a matrix configuration, offering low on-resistance, high-speed switching, and low power consumption. This makes it an ideal choice for applications requiring efficient signal routing, such as telecommunications, audio systems, and data acquisition systems.

• Audio signal routing and mixing
• Data acquisition systems
• Telecommunication systems
• Test and measurement equipment
• Sensor multiplexing

• Manufacturer: Adafruit
• Switch Configuration: Dual 4-channel (8:1 matrix)
• Supply Voltage Range: 2.7 V to 5.5 V
• On-Resistance (RON): 2.5 Ω (typical)
• Switching Time: 20 ns (typical)
• Power Consumption: Low power, <1 µA in standby mode
• Control Interface: I²C-compatible
• Operating Temperature Range: -40°C to +85°C

The ADG728 is typically available in a 16-lead TSSOP package. Below is the pin configuration:

1. Power Supply: Connect the VDD pin to a power supply within the range of 2.7 V to 5.5 V. Connect the GND pin to the ground of the circuit.
2. I²C Interface: Use the SCL and SDA pins to communicate with the ADG728 via an I²C-compatible microcontroller. Configure the I²C address using the A0 and A1 pins.
3. Signal Connections: Connect the analog signals to the S1A-S4A and S1B-S4B pins. The selected signals will be routed to the D1 and D2 pins, respectively.
4. Control: Use I²C commands to select the desired switch configuration. Each channel can be independently controlled.

• Signal Voltage Range: Ensure that the input signal voltage does not exceed the supply voltage (VDD).
• I²C Pull-Up Resistors: Use appropriate pull-up resistors on the SCL and SDA lines for proper I²C communication.
• Decoupling Capacitor: Place a 0.1 µF decoupling capacitor close to the VDD pin to reduce noise and improve stability.

Below is an example of how to control the ADG728 using an Arduino UNO:

#include <Wire.h> // Include the Wire library for I²C communication

#define ADG728_ADDR 0x70 // Default I²C address of the ADG728

void setup() {
  Wire.begin(); // Initialize I²C communication
  Serial.begin(9600); // Initialize serial communication for debugging

  // Select channel 1A (S1A to D1)
  selectChannel(0x01); // 0x01 corresponds to channel 1A
}

void loop() {
  // Main loop can be used to switch channels dynamically
}

// Function to select a specific channel on the ADG728
void selectChannel(uint8_t channel) {
  Wire.beginTransmission(ADG728_ADDR); // Start communication with ADG728
  Wire.write(channel); // Send the channel selection command
  Wire.endTransmission(); // End communication

  Serial.print("Channel selected: ");
  Serial.println(channel, HEX); // Print the selected channel for debugging
}

• The Wire.begin() function initializes the I²C communication.
• The selectChannel() function sends a command to the ADG728 to select a specific channel. The channel is specified as a hexadecimal value (e.g., 0x01 for channel 1A).

1. No Response from the ADG728

   • Cause: Incorrect I²C address or wiring.
   • Solution: Verify the I²C address and ensure proper connections to the SCL and SDA pins. Check the pull-up resistors on the I²C lines.

2. Signal Distortion

   • Cause: Input signal exceeds the supply voltage or poor grounding.
   • Solution: Ensure the input signal voltage is within the VDD range. Check the ground connections and add a decoupling capacitor near the VDD pin.

3. Switch Not Changing Channels

   • Cause: Incorrect I²C command or communication failure.
   • Solution: Double-check the I²C commands being sent. Use a logic analyzer to monitor the I²C communication.

Q1: Can the ADG728 handle digital signals?
A1: Yes, the ADG728 can switch both analog and digital signals, provided the signal voltage is within the supply voltage range.

Q2: How many devices can be connected on the same I²C bus?
A2: Up to 4 ADG728 devices can be connected on the same I²C bus by configuring the A0 and A1 address pins.

Q3: What is the maximum signal frequency the ADG728 can handle?
A3: The ADG728 is suitable for signals up to 10 MHz, depending on the load and circuit configuration.

Q4: Is the ADG728 bidirectional?
A4: Yes, the ADG728 supports bidirectional signal flow, making it versatile for various applications.