How to Use ICL7660 Charge-Pump Voltage Converter: Examples, Pinouts, and Specs

The ICL7660 is a charge-pump voltage converter designed to generate a negative voltage from a positive voltage supply. It operates by transferring charge between capacitors, enabling efficient voltage inversion without the need for inductors. This makes the ICL7660 a compact and cost-effective solution for applications requiring a negative voltage rail.

• Generating negative voltage rails for operational amplifiers
• Biasing circuits in analog systems
• LCD contrast adjustment
• Low-power, portable devices requiring dual power supplies
• General-purpose voltage inversion in battery-powered systems

The ICL7660 is a versatile and efficient device with the following key specifications:

The ICL7660 is typically available in an 8-pin DIP or SOIC package. Below is the pinout and description:

1. Power Supply: Connect the V+ pin to a positive voltage source (1.5V to 10V) and the GND pin to ground.
2. Charge-Pump Capacitors:
   • Connect a capacitor (typically 10µF) between CAP+ and CAP-.
   • Connect another capacitor (10µF or higher) between VOUT and GND to stabilize the output voltage.
3. Low Voltage Operation: If the input voltage is below 3.5V, connect the LV pin to GND to optimize performance.
4. Oscillator Control: For standard operation, leave the OSC pin unconnected or connect it to GND. For custom oscillator frequencies, an external clock signal can be applied to this pin.

Below is a basic circuit diagram for using the ICL7660 to generate a -5V output from a +5V input:

   +5V ----+------------------+------------------+
           |                  |                  |
          [C1]               [C2]               |
           |                  |                  |
          CAP+               VOUT               GND
           |                  |                  |
          CAP-               GND                |
           |                  |                  |
           +------------------+------------------+

• C1 and C2 are typically 10µF electrolytic capacitors.

The ICL7660 can be used in conjunction with an Arduino UNO to provide a negative voltage rail for analog circuits. Below is an example code snippet to demonstrate its use:

// Example: Using ICL7660 with Arduino UNO
// This code demonstrates how to read an analog signal that requires a negative
// voltage reference, powered by the ICL7660.

const int analogPin = A0; // Analog input pin connected to the signal

void setup() {
  Serial.begin(9600); // Initialize serial communication
  pinMode(analogPin, INPUT); // Set the analog pin as input
}

void loop() {
  int analogValue = analogRead(analogPin); // Read the analog signal
  float voltage = (analogValue / 1023.0) * 5.0; // Convert to voltage (0-5V range)
  
  // Print the voltage value to the Serial Monitor
  Serial.print("Analog Voltage: ");
  Serial.print(voltage);
  Serial.println(" V");
  
  delay(500); // Wait for 500ms before the next reading
}

• Use low-ESR capacitors (e.g., tantalum or ceramic) for optimal performance.
• Ensure the input voltage does not exceed the maximum rating of 10V.
• For higher output currents, use larger capacitors to reduce ripple voltage.
• Avoid excessive load currents, as this can cause the output voltage to drop significantly.
• If using the OSC pin for an external clock, ensure the frequency is within the recommended range (10kHz to 100kHz).

1. Output Voltage is Incorrect or Unstable:

   • Check the polarity and value of the capacitors.
   • Ensure the capacitors are low-ESR and properly connected.
   • Verify that the input voltage is within the specified range.

2. High Ripple on Output Voltage:

   • Increase the capacitance of the output capacitor (VOUT to GND).
   • Use capacitors with lower ESR for better filtering.

3. Device Overheating:

   • Ensure the load current does not exceed the maximum rating (20mA).
   • Verify that the input voltage is not too high.

4. No Output Voltage:

   • Check all connections and ensure the device is powered correctly.
   • Verify that the LV pin is connected to GND if the input voltage is below 3.5V.

Q1: Can the ICL7660 provide a regulated output voltage?
A1: The ICL7660 does not provide precise voltage regulation. The output voltage is approximately equal to -V+, minus a small voltage drop due to internal resistance.

Q2: Can I use the ICL7660 with input voltages above 10V?
A2: No, the maximum input voltage is 10V. Exceeding this limit may damage the device.

Q3: What happens if I omit the LV pin connection for low-voltage operation?
A3: If the LV pin is not connected to GND when the input voltage is below 3.5V, the device may not function correctly or may exhibit reduced efficiency.

Q4: Can I use the ICL7660 to generate a positive voltage?
A4: No, the ICL7660 is specifically designed for voltage inversion. For positive voltage generation, consider using a boost converter.

By following this documentation, users can effectively integrate the ICL7660 into their designs and troubleshoot common issues.