Combined voltage, current control loops simplify LED, solar apps

The rapid expansion of constant-current/constant-voltage (CC-CV) applications, especially in LED lighting and high capacity battery and supercapacitor chargers challenges power supply designers to keep pace with the increasingly complicated interplay of current and voltage control loops. A switch-mode converter designed specifically for CC-CV offers a clear advantage, especially when the supply has limited power, or its power is allocated among several competing loads.

Consider, for instance, the challenge of charging a supercapacitor in a minimum amount of time from a power-limited supply. To maintain constant input power, the controlled charging current must decrease as the output (supercapacitor) voltage increases. The LT3796 solves the problem of power limited or constant current/constant voltage regulation by seamlessly combining a current regulation loop and two voltage regulation loops to control an external N-channel power switch. The inherent wired-OR behavior of its three transconductance error amplifiers summed into the compensation pin, V_C, ensures that the correct loop (that is, the one closest to regulation) dominates.

The additional, standalone current sense amplifier can be configured for any number of functions, including input current limit and input voltage regulation.

The LT3796’s wide V_IN range (6V to 100V) and rail-to-rail (0V to 100V) output current monitoring and regulation allow it to be used in a wide variety of applications from solar battery chargers to high power LED lighting systems. The fixed switching frequency, current-mode architecture results in stable operation over a wide range of supply and output voltages. The LT3796 incorporates a high side current sense, enabling its use in boost, buck, buck-boost or SEPIC and flyback topologies.