Controller creates wide-input supplies

Edited by the Electronicstalk editorial team May 31, 2007

Current-mode programmable-frequency PWM controller reduces the size and complexity of flyback power supplies.

A new current-mode programmable-frequency PWM controller from Linear Technology reduces the size and complexity of flyback power supplies.

The LTC3805 contains all the features necessary to design high efficient single-ended isolated and nonisolated flyback convertors rated up to 25W for telecommunications, networking equipment, power-over-Ethernet, automotive, consumer and general housekeeping power supplies.

With its ultra low 40uA startup current, the IC allows the use of a high-value input resistor and a low-value capacitor for low power dissipation and quick power supply startup.

The LTC3805 is ideal for wide input voltage range applications where the input can vary from 9 to 72V during startup and will sustain operation from 4 to 72V after start up.

This enables users to create one power supply for both 48 and 24V nominal input systems.

With a standby quiescent current of only 360uA, makes it an excellent choice for automotive applications.

The LTC3805 can regulate output voltages as low as 0.8V and has an integrated soft-start function that limits inrush current, reducing output voltage overshoot.

Its micropower hysteretic startup circuit uses an internal Zener clamp to protect the part from input over voltage conditions.

The operating frequency is selectable from 70 to 700kHz by one external resistor or for noise sensitive requirements can be synchronised to the same range.

Constant frequency operation is maintained down to light loads, resulting is less low frequency noise generation over a wide range of load currents.

The 100mV current sense threshold allows the use of a very small current sense resistor, which helps maintain high efficiency.

With adjustable slope compensation, an LTC3805-based power supply achieves fast transient response with minimum output capacitance.

The LTC3805 is offered in a 10-lead 3 x 3mm DFN or 10-lead MSOP package and has an operating temperature range from -40 to +85C.

The 1000-piece price starts at US $1.39 each.