The LT3999 is a monolithic, high voltage, high frequency DC/DC transformer driver providing isolated power in a small solution footprint. 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. The input operating range is programmed with the precision undervoltage and overvoltage lockouts. The supply current is reduced to less than 1μA during shutdown. A user-defined RC time constant provides an adjustable soft-start capability by limiting the inrush current at start-up. The LT3999 is available in a 10-lead MSOP and 3mm × 3mm DFN package with exposed pad.