Step-down controller operates at up to 2.25MHz

The LTC7800, a synchronous step-down DC/DC controller from Linear Technology (recently acquired by Analogue Devices), is said to operate at up to 2.25MHz.

The controller’s low 45ns minimum on-time enables 24VIN to 3.3VOUT conversions while switching at a fixed 2MHz, avoiding critical noise-sensitive frequency bands, including AM radio. Synchronous rectification is claimed to deliver up to 95% efficiency while Burst Mode operation keeps quiescent current under 50μA in no-load standby conditions.

According to the company, the LTC7800 operates over a 4 to 60V input supply range designed to protect against high voltage transients, to cover a range of input sources and battery chemistries, and for continuous operation during automotive cold crank. The output voltage can be set from 0.8 to 24V at output currents up to 20A.

Complete with 1.1Ω on-chip MOSFET gate drivers, the controller operates with a selectable fixed frequency between 320kHz and 2.25MHz and is synchronisable to an external clock over the same range.

The user can select from continuous operation, pulse-skipping and low ripple Burst Mode operation during light loads. Output current sensing is accomplished by measuring the voltage drop across the output inductor (DCR) for the highest efficiency or by using an optional sense resistor.

Current foldback limits MOSFET heat dissipation during overload conditions. Additional features include up to 98% duty cycle; an internal LDO that powers the gate drive from the input voltage or EXTVCC; and a power good output signal.

The LTC7800 is available in a 20-lead 3 x 4mm QFN thermally enhanced package which is pin compatible to the LTC3891. Two operating junction temperature grades are available from -40 to 125°C and an automotive grade version from -40 to 150°C.

Applications include automotive, heavy equipment, industrial control, robotics and telecom.

Peggy Lee