How to Use LTC7890-BZ: Examples, Pinouts, and Specs

The LTC7890-BZ, manufactured by Analog Devices, is a high-performance synchronous step-down DC/DC controller designed for efficient and compact power supply solutions. It supports a wide input voltage range and employs advanced control techniques to deliver a stable and precise output voltage, even under dynamic load conditions. This component is ideal for applications requiring high efficiency, compact design, and robust performance.

• Industrial power supplies
• Automotive systems
• Telecommunications equipment
• Distributed power architectures
• High-performance computing systems

• Input Voltage Range: 4.5V to 60V
• Output Voltage Range: 0.8V to 24V
• Switching Frequency: Adjustable from 100kHz to 3MHz
• Efficiency: Up to 95% (depending on configuration)
• Output Current: Up to 25A (with appropriate external components)
• Control Mode: Current-mode or voltage-mode control
• Operating Temperature Range: -40°C to 125°C
• Package: 28-lead TSSOP (Thermally Enhanced)

The LTC7890-BZ is housed in a 28-lead TSSOP package. Below is the pin configuration and description:

1. Input and Output Connections:

   • Connect the input voltage source to the VIN pin.
   • Use a suitable inductor and capacitor at the output to filter the voltage and connect the load.

2. Setting the Output Voltage:

   • Use a resistor divider network connected to the FB pin to set the desired output voltage. The formula is: [ V_{OUT} = V_{REF} \times \left(1 + \frac{R1}{R2}\right) ] where ( V_{REF} ) is typically 0.8V.

3. Compensation:

   • Connect a capacitor and resistor to the ITH pin to stabilize the control loop. Refer to the datasheet for recommended values based on your application.

4. Soft-Start:

   • Connect a capacitor to the SS pin to control the startup time. A larger capacitor results in a slower startup.

5. Synchronization:

   • If required, connect an external clock to the SYNC pin to synchronize the switching frequency.

6. Enable the Controller:

   • Pull the RUN pin high to enable the LTC7890-BZ. Use a resistor divider if you need to set a specific undervoltage lockout threshold.

• Thermal Management: Ensure proper heat dissipation by using a PCB with adequate copper area around the VIN, SW, and GND pins.
• Input Capacitor: Use low-ESR capacitors at the input to minimize voltage ripple.
• Inductor Selection: Choose an inductor with sufficient current rating and low DC resistance to optimize efficiency.
• Output Capacitor: Select capacitors with low ESR to ensure stable operation and low output voltage ripple.
• PCB Layout: Follow the recommended layout guidelines in the datasheet to minimize noise and improve performance.

The LTC7890-BZ can be used in conjunction with an Arduino UNO for monitoring or controlling its operation. Below is an example code snippet to monitor the power good (PG) signal:

// Define the pin connected to the PG (Power Good) signal
const int pgPin = 2; // Connect PG pin of LTC7890-BZ to Arduino digital pin 2

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

void loop() {
  int pgStatus = digitalRead(pgPin); // Read the PG signal

  if (pgStatus == HIGH) {
    // PG signal is high, output voltage is within regulation
    Serial.println("Power Good: Output voltage is stable.");
  } else {
    // PG signal is low, output voltage is out of regulation
    Serial.println("Warning: Output voltage is not stable!");
  }

  delay(1000); // Wait for 1 second before checking again
}

1. Output Voltage is Incorrect:

   • Verify the resistor divider network connected to the FB pin.
   • Check for proper connections and soldering on the PCB.

2. Controller Does Not Start:

   • Ensure the RUN pin is pulled high.
   • Check the input voltage to ensure it is within the specified range.

3. Excessive Output Ripple:

   • Use low-ESR capacitors at the output.
   • Verify the inductor value and ensure it meets the design requirements.

4. Overheating:

   • Check for proper thermal management and ensure adequate PCB copper area.
   • Verify that the input and output currents are within the specified limits.

Q1: Can the LTC7890-BZ operate without an external clock?
A1: Yes, the LTC7890-BZ has an internal oscillator and does not require an external clock. However, you can synchronize it to an external clock using the SYNC pin if needed.

Q2: What is the maximum output current the LTC7890-BZ can handle?
A2: The maximum output current depends on the external components, such as the MOSFETs and inductor. With appropriate components, it can support up to 25A.

Q3: How do I calculate the soft-start time?
A3: The soft-start time can be calculated using the formula: [ t_{SS} = \frac{C_{SS} \times V_{REF}}{I_{SS}} ] where ( C_{SS} ) is the soft-start capacitor, ( V_{REF} ) is 0.8V, and ( I_{SS} ) is the soft-start charging current (refer to the datasheet for the exact value).

Q4: Can I use the LTC7890-BZ in automotive applications?
A4: Yes, the wide input voltage range and robust design make it suitable for automotive systems. Ensure compliance with automotive standards as required.