Electronic Design

95% Efficient Step-Down DC-DC Controllers Boast Wide Input Range

The LTC3878 and LTC3879 high-efficiency synchronous step-down dc-dc controllers from Linear Technology target distributed power supplies, embedded computing, and other point-of-load (POL) regulation applications. Their constant on-time valley current-mode control and 43-ns minimum on-time allow very low duty cycles, which is ideal for high step-down ratios and an extremely fast transient response, the company says. Both parts also feature an input voltage range of 4 to 38 V. The strong on-board N-channel MOSFET driver allows the use of high-power external MOSFETs to produce output currents with efficiency as high as 95%.

The LTC3878 has an output voltage range of 0.8 V to 90% of VIN, whereas the LTC3879 has an output range of 0.6 V to 90% of VIN. Both controllers are designed to be stable with all-ceramic output capacitor designs for space-constrained applications. The operating frequency is programmed with an external resistor and allows for up to 1-MHz switching. No sense resistor is required, and the output current is measured by sensing the voltage drop across the synchronous MOSFET.

Selectable continuous or discontinuous mode operation provides high efficiency at light load and safely powers up into pre-biased outputs. Both parts have programmable current limit, and the output current folds back during an overload condition. They have a ±1% accurate voltage reference from a –40°C to 85°C operating temperature range. System supervisory ICs, microcontrollers, and DSPs all benefit from the LTC3879’s output voltage tracking for flexible startup and shutdown sequencing. Additional features include programmable soft start, a power good output and over voltage protection.

The LTC3878 is housed in a narrow 16-pin SSOP package and is pin-to-pin compatible with the LTC1778 for an easy upgrade path. The LTC3879 is offered in thermally enhanced 3- by 3-mm QFN-16 and MSOP-16E packages. Pricing starts at $2.20 each in 1000-piece quantities.

Linear Technology


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