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60V Input DC/DC Synchronous Step-Down Controller with Adjustable Frequency Optimizes Size and Efficiency

7th August 2007

Linear Technology (UK) Limited

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Linear Technology has introduced the LT3845, a 4V to 60V input range, synchronous DC/DC step-down controller with adjustable 100kHz to 500kHz operating frequency. At higher frequencies users can implement a smaller inductor and capacitors, or at lower frequencies they can optimize the efficiency of the circuit. For noise- sensitive applications, the LT3845 can be synchronized to an external clock from 100kHz to 600kHz. The minimum 4V input maintains operation during automotive cold cranking and the 60V maximum input withstands inductive load dump peak voltages. In addition, the output voltage can be adjusted over a wide range from 1.23V to 36V at load currents up to 20A. Applications include 12V and 42V automotive, 48V telecom supplies, heavy equipment systems, avionics, industrial controls and distributed power systems.

The LT3845 is a current mode controller with an integrated biasing regulator that drives N-channel MOSFETs. Current mode operation provides fast line and load transient response, as well as cycle-by-cycle overcurrent protection. The integrated regulator provides IC power directly from the input supply without the need for a separate bias voltage. It maintains high efficiency at light loads with its Burst Mode® operation and 120uA quiescent current, a feature required in many automotive and battery-supplied input applications. Other features include short-circuit protection, adjustable soft-start, thermal shutdown and precision input undervoltage lockout. The LT3845 employs adaptive overlap control, which maintains a constant dead time, preventing shoot-through switch currents, independent of the type, size or operating conditions of the external MOSFET switches.

The LT3845 is offered in a 16-pin thermally enhanced TSSOP package and is rated for operation from -40°C to 125°C. The 1,000-piece price starts at $3.56.