1. Overview & Function

️· What it is: The MIC2290 is a constant frequency, PWM (Pulse Width Modulation) current-mode boost regulator. Boost regulators increase a DC input voltage to a higher DC output voltage.
️· How it works:
- Uses a 1.2MHz oscillator.
- Includes slope compensation.
- Uses a current amplifier to measure switch current.
- Compares feedback voltage (from output) with an internal 1.24V reference (via feedback resistors).
- PWM generator controls the output transistor, switching it on and off to regulate the output voltage.
️· Block Diagram: (Refer to Figure 1 in the document - not reproduced here). It shows VIN, FB (Feedback), EN (Enable), OUT, and key internal blocks.

2. Functional Description Details

️· PWM Control: The regulator uses a constant frequency PWM technique. The output transistor is switched on and off based on comparisons between the current loop signal and the voltage loop signal.
️· Feedback: The output voltage is regulated through feedback resistors (R1 and R2) that determine the voltage applied to the feedback pin. The desired output voltage can be calculated using a formula (see below).

3. Applications & Component Selection

️· Typical Application Circuit: (Refer to Figure 2) Shows a boost circuit with an inductor (L1), input capacitor, output capacitor, and the MIC2290.
️· Duty Cycle:
- The duty cycle (on/off time ratio) is a critical parameter. A maximum duty cycle of 85% is recommended to ensure proper operation.
️· Inductor Selection:
- Recommended inductance: 10µH (a good balance between cost, size, performance).
- Larger inductors reduce ripple current and improve efficiency, but may require increased output capacitance to maintain stability.
- Right Half Plane Zero (RHPZ) frequency calculation is provided to determine capacitor requirements.
️· Output Capacitor Selection:
- X5R or X7R ceramic capacitors are recommended.
- Capacitance values vary based on the desired output voltage. Refer to Table 1 for guidelines.
️· Input Capacitor: Minimum 1µF ceramic capacitor recommended.
️· Feedback Resistors: Used to set the output voltage. The output voltage is determined by R1 and R2, using this equation:

```
V_OUT = 1.24V * (R1 / R2) + 1.24V
```

Where V_OUT is the desired output voltage.

4. Protection & Other Features

️· Overvoltage Protection (OVP): The MLF™ package option includes an overvoltage protection function. If the feedback pin is shorted to ground, the switch will shut off to prevent damage.
️· Right Half Plane Zero: A consideration for component selection.

5. Specific Numerical Values from the Text

️· Oscillator Frequency: 1.2 MHz
️· Reference Voltage (VREF): 1.24V
️· Maximum Duty Cycle: 85%
️· Recommended Inductance (L1): 10µH
️· Minimum Input Capacitor: 1µF