High-input flyback controller serves extended temperature range

March 20, 2015 // By Christoph Hammerschmidt
Being available now also for the military temperature range (-55°C to 150°C), the LT3748 isolated flyback DC/DC converter can be deployed in automotive, industrial, telecom and other applications with increased reliability requirements. The converter does not require an opto-isolator, third winding or signal transformer for feedback since the output voltage is sensed from the primary-side flyback signal - a feature that greatly simplifies the design of an isolated DC/DC converter.

The LT3748 operates over a 5V to 100V input voltage range and drives an external N-channel power MOSFET. It 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, undervoltage lockout, adjustable current limit and output voltage temperature compensation.
The LT3748MP operating junction temperature is from -55°C to 150°C and the device is housed in a MSOP-16 package with 4 pins removed for additional high voltage pin spacing. Its features include

•    Current Mode Control
•    Boundary Mode Operation
•    VOUT Set with Two External Resistors
•    Off-the-Shelf Transformers
•    Programmable Soft-Start
•    Programmable Under Voltage Lockout
•    Output Voltage Temperature Compensation

For more information, visit www.linear.com/product/LT3748