1. Overview & Key Features

️· LM3487: A switching regulator designed for flexibility and performance. It's intended for applications requiring adjustable operation and component selection.
️· Current Mode Control: Uses current mode control, enabling cycle-by-cycle current limiting and simplifying loop compensation.
️· Adjustable Slope Compensation: Includes a default slope compensation, which can be externally increased for smaller inductor selection.
️· Soft-Start: A soft-start circuit gradually increases the output voltage to prevent inrush current, controlled by an external capacitor. Also supports shutdown functionality.
️· Input Under Voltage Lockout (UVLO): Disables operation if the input voltage drops below a specified level (2.80V typical).
️· Current Limit Protection: Limits the output current to protect the components.
️· Short Circuit Protection: Provides enhanced protection under short-circuit conditions, disabling the MOSFET for a limited number of cycles.
️· Flexible Component Selection: Allows for many design tradeoffs to optimize performance or component availability.

2. Operational Details & Design Considerations

️· Subharmonic Oscillation Prevention: Current mode control can lead to subharmonic oscillation, which is mitigated by the adjustable slope compensation. The slope compensation must be increased if using smaller inductors.
️· Soft-Start Circuitry:
- Start-up delay (0-0.75V) determined by the softstart current and capacitance.
- Soft-start ramp (0.75V-2V) determined by softstart current and capacitor.
- Shutdown can be enabled by grounding the SS/SD pin.
️· UVLO Operation: Disables the regulator if input voltage is too low.
️· Current Limiting: Protects components by limiting output current. Includes a secondary short circuit protection for high current fault conditions.
️· Short Circuit Protection: Provides a temporary shutdown in the event of a short circuit condition.
️· Design Flexibility:
- Inductor Selection: Adjustable slope compensation allows for flexibility in inductor value.
- Current Limit Setting: Sense resistor is used to adjust the current limit.
- Component Optimization: Allows tradeoffs in component selection for various performance goals.

3. Important Design Parameters (Values are *typical* unless stated otherwise)

️· UVLO Threshold: 2.80V
️· Soft-Start Delay: Determined by external capacitor (Css) and the 2µA current source.
️· Soft-Start Voltage Range: 0V to 2V
️· Shutdown Voltage (SS/SD pin): Below 0.7V
️· Current Limit Threshold (VCL): Specified in Electrical Characteristics
️· Short Circuit Protection Threshold (VSC): Specified in Electrical Characteristics



Overall, the LM3487 offers a lot of control over regulator behavior, allowing designers to tailor its operation to meet specific application requirements. Careful consideration of the design parameters and potential instability issues is crucial for optimal performance.