High input voltage isolated fly-back DC-DC controller for tough environments

Linear Technology has announced a new military MP grade version of the LT3748, a high input voltage isolated fly-back DC-DC controller. The device simplifies the design of an isolated DC-DC converter by not requiring an opto-isolator, third winding or signal transformer for feedback since the output voltage is sensed from the primary-side fly-back signal. The LT3748 operates over a 5V to 100V input voltage range and drives an external N-channel power MOSFET, making it well suited to a wide variety of automotive, industrial, telecom and datacom applications. The LT3748 operates in boundary mode, which is a variable frequency current mode control switching scheme, resulting in +/-5% typical regulation over the full line, load and temperature range. Boundary mode also permits the use of a smaller transformer compared to equivalent continuous conduction mode designs. The output voltage is easily set by two external resistors and the transformer turns ratio. Several off-the-shelf transformers are identified in the data sheet that can be used for numerous applications. The high level of integration and the use of boundary mode operation results in a simple, clean application solution to the traditionally tough problem of isolated power delivery. Additional features include an onboard low drop regulator for IC power, programmable soft start, under-voltage lockout, adjustable current limit and output voltage temperature compensation. The LT3748MP operating junction temperature is from -55C to 150C and the device is housed in a MSOP-16 package with 4 pins removed for additional high voltage pin spacing.