Linear Technology Corporation has introduced the LT3845, a synchronous dc/dc step-down controller for 12 V and 42 V automotive power systems. The LT3845 features a 4 V to 60 V input range and an operating frequency adjustable from 100 kHz to 500 kHz. Users can implement a smaller inductor and capacitors at higher frequencies, or can optimize the efficiency of the circuit at lower frequencies.
For noise-sensitive applications, the LT3845 can be synchronized to an external clock from 100 kHz to 600 kHz. A minimum 4 V input maintains operation during automotive cold cranking, and the 60 V maximum input withstands inductive load dump peak voltages. Output voltage can be adjusted over a range from 1.23 V to 36 V at load currents up to 20 A.
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, according to the company. An integrated regulator provides IC power directly from the input supply without the need for a separate bias voltage.
The device maintains high efficiency at light loads with burst mode operation and 120 µA quiescent current as required in many automotive 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 device is available in a 16-pin thermally enhanced TSSOP package and is rated for operation from -40 °C to 125 °C.