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PWM controller simplifies flyback power supplies

Posted: 05 Feb 2007 ?? ?Print Version ?Bookmark and Share

Keywords:PWM controller? flyback? DC/DC? Linear? power supplies?

Linear Technology Corp. has introduced the LTC3805, a current mode, programmable frequency PWM controller that reduces the size and complexity of flyback power supplies. This device contains all the features necessary to design highly efficient, single-ended isolated and non-isolated flyback converters rated up to 25W for telecom, networking equipment, PoE, automotive, consumer and general housekeeping power supplies. With its ultralow 40?A start-up 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 start-up.

Automotive apps
The LTC3805 is suitable for wide input voltage range applications where the input can vary from 9V to 72V during start-up and will sustain operation from 4V to 72V after start up. This enables users to have one power supply for both 48V and 24V nominal input systems. With a standby quiescent current of only 360?A, the device is suitable 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 micro power hysteretic start-up circuit uses an internal Zener clamp to protect the part from input overvoltage conditions. The operating frequency is selectable from 70kHz to 700kHz by one external resistor, or can be synchronized to the same range for noise-sensitive applications.

High efficiency
Constant frequency operation is maintained down to light loads, resulting in less low-frequency noise over a wide range of load currents. The 100mV current sense threshold allows the use of a small current sense resistor, which helps maintain 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-by-3mm DFN or 10-lead MSOP package and has an operating temperature range from -40C to 85C. The 1,000-piece price starts at $1.39 each.

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Related Datasheets
Part Number Description Category
? LTC3805 Adjustable Frequency Current Mode Flyback DC/DC Controller ICs, Interface



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