DC1566A - Schematic10/6/2009
Demonstration circuit 1566 is a monolithic stepdown DC/DC switching regulator featuring the LT3970. The switching frequency is adjustable up to 2MHz. The demo circuit is designed for 5V, 350mA output from a 6V to 40V input. The wide input range of the LT3970 allows a variety of input sources including automotive batteries and 24V industrial supplies. Low ripple Burst Mode increases the efficiency at the light load while keeping the output ripple below 15mV. The part is in shutdown when the EN pin is low and active when the pin is high. The threshold of the EN pin is accurate at 1V when Vin is above 4.2V. Adding a resistor divider from Vin to EN can program the LT3970 to regulate the
output only when Vin is above a desired voltage. The catch diode and boost diode are integrated to reduce the components count and solution size. The circuit consumes only 2μA of quiescent current. The current mode control scheme creates fast transient response and good loop stability. The catch diode current is limited to protect the part under short circuit and overvoltage conditions.