DC1221B - Schematic3/18/2011
Demo circuit DC1221B is a monolithic step-down DC/DC switching regulator featuring the LT3502. The demo circuit is designed for 3.3V output from a 4.5V to 40V input. The wide input range of the LT3502 allows a variety of input sources including automotive batteries and 24V industrial supplies. The high switching frequency allows the use of tiny, low cost external components. The current mode control scheme creates fast transient response and good loop stability. The boost diode is internal to reduce component count. The SHDN pin can also be used to program soft start. In this mode, the SHDN pin is driven through an external RC filter to create a voltage ramp on this pin. The soft start function reduces the input current surge during start-up. Cycle by cycle current limit and frequency foldback provide the protection against shorted outputs. DA pin can further protect the silicon under fault conditions by sensing the diode current.