LTC7818 Synchronous Controller

ADI's LTC7818 combines a boost with two step-down controllers in a single package. A 12-volt car battery can dip below 5 V during an engine restart, which can cause infotainment systems and other electronic devices requiring 5 V and higher to reset. The LTC7818 prevents this problem by providing a synchronous boost that delivers 10 V to the two step-down converters during a restart. This method allows all output voltages to remain in regulation during restart since the boost converter can operate down to 1 V after startup. When the input voltage from the car battery is higher than 10 V, the boost converter runs at 100% duty cycle (PassThru^TM) and simply passes the input voltage to the step-down converters reducing power loss and eliminating EMI.

Demonstration circuit DC2855A is a triple-output synchronous step-up/dual step-down supply featuring the LTC7818. The demonstration circuit is designed for two buck outputs (5 V / 10 A, 3.3 V / 10 A) supplied by a boosted 10 V output. Benefiting from this feature, the buck outputs can maintain regulation over a wide input voltage range of 4.5 V to 36 V which is suitable for automotive or other battery-fed applications. Also, the demonstration circuit uses a drop-in layout whereas the main buck circuit components fit in an area of ¾” by 1½”, while the main boost circuit area is ¾” by 1¾”. The package style for the LTC7818 is a 40-pin exposed pad QFN.

The main features of the board include rail tracking (buck channels only), an internal 5 V linear regulator for bias, separated RUN pins for each output, a PGOOD signal (CH1 only), an overvoltage indicator for CH3, and a mode selector that allow the converter to run in CCM, pulse skipping or burst mode operation. Spread spectrum mode is available for EMI improvement. Synchronization to an external clock is also possible.

Features

• Boost + dual buck synchronous controllers allow all outputs to remain in regulation during automotive restart or cold crank
• V_IN range of 4.5 V to 40 V (and operates down to 1 V after startup)
• Low 14 µA operating quiescent current extends the battery run time during a standby condition

Applications

• Automotive: start/stop systems when powering Infotainment, cabin electronics, and audio systems
• General purpose: triple-output controller for industrial, avionics, and military applications