Auto Electronics

Linear Tech PWM controller simplifies flyback power supplies

Linear Technology Corporation has introduced the LTC3805, a current mode, programmable frequency pulse width modulation (PWM) controller said to reduce the size and complexity of flyback power supplies. Linear said the device contains all the features necessary to design highly efficient, single-ended, isolated and non-isolated flyback converters rated up to 25 W for automotive and other power supplies. Featuring 40 µA start-up current, the integrated circuit allows the use of a high-value input resistor and a low-value capacitor for low power dissipation and quick power supply start-up.

The LTC3805 is suited for wide input voltage range applications where the input can vary from 9 V to 72 V during start-up and will sustain operation from 4 V to 72 V after start up. This enables users to have one power supply for both 48 V and 24 V nominal input systems. A standby quiescent current of 360 µA commends the device for automotive applications.

The LTC3805 can regulate output voltages as low as 0.8 V. An integrated soft-start function limits inrush current, reducing output voltage overshoot. The device’s micropower hysteretic start-up circuit uses an internal Zener clamp to protect the part from input overvoltage conditions. The operating frequency is selectable from 70 kHz to 700 kHz by one external resistor, or it can be synchronized to the same range for noise-sensitive requirements. Constant frequency operation is maintained down to light loads, resulting in less low-frequency noise generation over a wide range of load currents. A 100 mV 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 can achieve fast transient response with minimum output capacitance, according to the company.

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

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