How to Use lm8705: Examples, Pinouts, and Specs

The LM8705 is a high-performance, low-dropout (LDO) voltage regulator designed to provide a stable output voltage with low noise and high efficiency. It is ideal for applications requiring precise voltage regulation, such as battery-powered devices, portable electronics, and sensitive analog circuits. Its low dropout voltage and high power supply rejection ratio (PSRR) make it suitable for noise-sensitive environments.

• Battery-powered devices (e.g., smartphones, wearables)
• Portable electronics
• Analog and RF circuits requiring low noise
• Microcontroller and digital logic power supplies
• Industrial and automotive systems

1. Input Capacitor: Connect a capacitor (typically 10 µF) between the VIN pin and ground to stabilize the input voltage and reduce noise.
2. Output Capacitor: Connect a low-ESR capacitor (typically 10 µF or higher) between the VOUT pin and ground to ensure stable operation and minimize output voltage ripple.
3. Adjustable Output (if applicable): For adjustable versions, connect a resistor divider network to the feedback pin to set the desired output voltage.
4. Thermal Considerations: Ensure proper heat dissipation by using a heatsink or PCB thermal vias, especially for high-current applications.
5. Wiring: Keep the input and output capacitor connections as close to the regulator pins as possible to minimize noise and improve stability.

Below is an example of using the LM8705 to regulate a 5V output from a 12V input:

   +12V Input
       |
      [C1] 10 µF
       |
      VIN (Pin 1)
       |
      LM8705
       |
      VOUT (Pin 3) -----> +5V Output
       |
      [C2] 10 µF
       |
      GND (Pin 2)
       |
     Circuit Ground

The LM8705 can be used to power an Arduino UNO with a stable 5V supply. Below is an example code snippet to demonstrate its use in a simple LED blink circuit:

// Example: Blink an LED using Arduino UNO powered by LM8705
// Ensure the LM8705 provides a stable 5V to the Arduino's 5V pin.

const int ledPin = 13; // Pin connected to the onboard LED

void setup() {
  pinMode(ledPin, OUTPUT); // Set the LED pin as an output
}

void loop() {
  digitalWrite(ledPin, HIGH); // Turn the LED on
  delay(1000);                // Wait for 1 second
  digitalWrite(ledPin, LOW);  // Turn the LED off
  delay(1000);                // Wait for 1 second
}

• Input Voltage: Ensure the input voltage is at least 0.3V higher than the desired output voltage to maintain regulation.
• Thermal Management: Use proper cooling methods to prevent overheating, especially at high currents.
• Capacitor Selection: Use low-ESR capacitors for stable operation. Ceramic or tantalum capacitors are recommended.

1. Output Voltage Instability

   • Cause: Insufficient or incorrect output capacitor.
   • Solution: Use a low-ESR capacitor with a value of at least 10 µF.

2. Excessive Heat

   • Cause: High input-to-output voltage difference or insufficient cooling.
   • Solution: Use a heatsink or improve PCB thermal dissipation. Reduce the input voltage if possible.

3. No Output Voltage

   • Cause: Incorrect wiring or damaged component.
   • Solution: Verify connections and ensure the input voltage is within the specified range.

4. High Noise on Output

   • Cause: Poor capacitor placement or insufficient input filtering.
   • Solution: Place capacitors close to the regulator pins and use higher-value input capacitors.

Q: Can the LM8705 be used with a 3.3V output?
A: Yes, the LM8705 can provide a 3.3V output if the input voltage is at least 3.6V (to account for the dropout voltage).

Q: What is the maximum current the LM8705 can supply?
A: The LM8705 can supply up to 1.5A of output current, provided proper thermal management is in place.

Q: Can I use electrolytic capacitors with the LM8705?
A: While electrolytic capacitors can be used, low-ESR ceramic or tantalum capacitors are recommended for optimal performance.

Q: How do I calculate the resistor values for an adjustable version?
A: Use the formula:
[ V_{OUT} = V_{REF} \times \left(1 + \frac{R1}{R2}\right) ]
where ( V_{REF} ) is typically 1.25V, and ( R1 ) and ( R2 ) are the resistors in the feedback network.

By following this documentation, users can effectively integrate the LM8705 into their designs for reliable and efficient voltage regulation.