LT3999 DC-DC Transformer Driver Analog Devices Inc. LT3999 DC-DC Transformer Driver is a monolithic, high-voltage, high-frequency, push-pull DC-DC driver designed to provide isolated power in a small solution footprint. The LT3999 includes functions such as duty cycle control, soft start, and protection features such as overvoltage lockout (OVLO), undervoltage lockout (UVLO), and thermal shutdown. The LT3999 has two 1A current limited power switches that switch out of phase. The duty cycle is programmable to adjust the output voltage. The switching frequency is programmed up to 1MHz and can be synchronized to an external clock for more accurate placement of switcher harmonics.