Microwave Journal

ADI Synchronous Step-Down Controller Operates for High-Power Density

May 31, 2017

Analog Devices, Inc., which recently acquired Linear Technology Corporation, announces the LTC7800, a synchronous step-down DC/DC controller that operates at up to 2.25 MHz for reduced circuit size and increased power density. Its low 45 ns minimum on-time enables 24 VIN to 3.3 VOUT conversions while switching at a fixed 2 MHz, avoiding critical noise-sensitive frequency bands including AM radio.

Synchronous rectification delivers up to 95 percent efficiency while Burst Mode® operation keeps quiescent current under 50 μA in no-load standby conditions, ideal for always-on systems.

The LTC7800 operates over a 4 to 60 V input supply range designed to protect against high voltage transients, continuous operation during automotive cold crank and to cover a broad range of input sources and battery chemistries. The output voltage can be set from 0.8 to 24 V at output currents up to 20 A, well suited for 12 or 24 V automotive, heavy equipment, industrial control, robotics and telecom applications.

The LTC7800 has powerful 1.1 Ω on-chip MOSFET gate drivers. It operates with a selectable fixed frequency between 320 kHz and 2.25 MHz and is synchronizable 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. Its current mode architecture provides easy loop compensation, fast transient response and excellent line regulation. 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 percent duty cycle (useful when powered from a battery during discharge), 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 mm x 4 mm QFN thermally enhanced package which is pin compatible to the LTC3891. Two operating junction temperature grades are available with extended and industrial versions from –40°C to 125°C and a high temp automotive grade version from –40°C to 150°C. The 1,000-piece price starts at $3.47 each. For more information, visit www.linear.com/product/ltc7800.