DC2285A: 48V @ 20A, 36 ~ 75V in Buck/Boost

Demonstration circuit 2285A features two high power high performance buck-boost LT®8705A converters operating in master-slave configuration. The circuit can operate with input voltages above, below or equal to the output voltage. The demo board input range is 36V to 75V. The output is optimized for 48V at 18A, with the output current limit set at 20A. The circuit will operate with lower input voltage than 36V if load current is reduced.

The LT8705A controller has integrated input current, input voltage, output current and output voltage regulators. The one regulator that wants to decrease current gets control over the compensation pin VC. The inductor current is controlled by the VC signal that is fed into a current comparator together with a ramp compensation signal.

The operating mode of the controller is determined through the MODE pin (jumper JP1) and can be set to discontinuous mode, forced continuous mode and Burst Mode operation.

The SYNC inputs are used to synchronize the two LT8705A power stages with 180-degree phase shift. The DC2285A demo board contains a multiphase clock.

The DC2285A demo board includes an LT8631 buck regulator that is configured for 7.8V. By connecting this low voltage to VIN and EXTVCC the power dissipation is reduced. The auxiliary 7.8V can also be used to power external circuitry.

The LT8705A data sheet gives a complete description of the part, operation and application information. The data sheet should be read in conjunction with this quick start guide for demo circuit 2285A. The DC2285A demo board has an optional signal interface that makes it easy to add potentiometers and switches (or a microcontroller) for accurate external control of the power stages.

The DC2285A circuit board has mounting holes for an optional heat sink and NTC resistor for monitoring heat sink temperature.