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Isolated monolithic flyback regulator simplifies design, eliminates optocoupler

August 02, 2010 // Paul Buckley

Isolated monolithic flyback regulator simplifies design, eliminates optocoupler

Linear Technology Corporation has unveiled an isolated monolithic flyback switching regulator that simplifies the design of an isolated DC/DC converter.

No opto-isolator, third winding or signal transformer are required for feedback since the output voltage is sensed from the primary-side flyback signal. The LT3575 operates over a 3 V to 40 V input voltage range, has a 2.5 A power switch and delivers up to 14 Watts of output power, making it well suited for a wide variety of industrial, medical, telecom, datacom and automotive applications.

The LT3575 operates in boundary mode, which is a variable frequency current-mode control switching scheme, typically resulting in +/-5 percent 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, identified in the data sheet, 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 dropout regulator for IC power, programmable soft-start, undervoltage lockout, adjustable current limit and output voltage temperature compensation.

Summary of Features: LT3575

  • VIN Range from 3 V to 40 V
  • Onboard 2.5 A, 60 V Integrated Power Switch
  • No Transformer, Third Winding or Opto-Isolator Required for Feedback
  • Current-Mode Control
  • Boundary-Mode Operation
  • VOUT Set with Two External Resistors
  • Off-the-Shelf Transformers
  • Programmable Soft-Start
  • Programmable Undervoltage Lockout
  • Output Voltage Temperature Compensation
  • Adjustable Current Limit
The LT3575 is available in a small thermally enhanced TSSOP-16 package and is offered in an extended and industrial operating junction temperature range from -40 to 125 degrees C. Pricing starts at 3.50 US Dollars each in 1000-piece quantities.

Related link: LT3575

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