The programmable duty cycle and turns ratio of the transformer sets the output voltage. Several off-the-shelf transformers shown in the data sheet simplify the design. The switching frequency is adjustable from 50kHz to 1MHz and can be synchronized to an external clock.

The LT3999 input operating voltage range is set with the precise 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 and an onboard cross-conduction prevention circuit increases reliability.

The LT3999 is available in thermally enhanced MSOP-10 and 3mm x 3mm DFN-10 packages. The LT3999 E- and I-grade versions operate from a –40°C to 125°C junction temperature. The LT3999 H grade is guaranteed to operate from a –40°C to 150°C operating junction temperature. The LT3999 MP grade is guaranteed to operate from –55°C to 150°C operating junction temperature.

Features:

－ Wide VIN Range: 2.7V to 36V

－ Dual 1A Switches

－ Programmable Switching Frequency: 50kHz to 1MHz

－ Synchronizable to an External Clock up to 1MHz

－ Duty Cycle Control for Output Voltage Regulation

－ Low Noise Topology

－ Programmable Input Over & Undervoltage Lockout

－ Cross-Conduction Prevention Circuitry

－ Extended & Industrial Grades: –40°C to 125°C Operating Junction Temp

－ Automotive Temp Grade: –40°C to 150°C Operating Junction Temp

－ Military Temp Grade: –55°C to 150°C Operating Junction Temp