Controller Drives N-Channel MOSFETs With No External Gate Supply

A synchronous step-down dc-dc controller, the LTC3822, accepts 2.75-V to 4.5-V inputs and drives an N-channel MOSFET without the need for an external supply for gate drive. In addition, the IC uses the MOSFET’s RDS(ON) sensing current, eliminating the need for a sense resistor, which improves efficiency and reduces overall costs. The device also can operate at 99% duty cycle for very low-dropout regulation. Designers can adjust operating frequency from 300 kHz to 750 kHz to optimize their system for size, noise, and efficiency.

Applications include point-of-load conversion from 3.3 V in and portable devices with single Li-ion batteries for load requirements up to 20 A. The LTC3822’s output is adjustable from 0.6 V to 99% of the input voltage. Internal soft-start circuitry ensures proper regulation and a controlled startup to minimize in-rush current. The device consumes 340 μA during operation and only 7.5 μA in shutdown mode. The LTC3822 comes in either a 10-lead MSOP or a smaller, 3-mm by 3-mm DFN package’s rated for operation from –40°C to 85°C.