Isolated monolithic flyback switching regulator eliminates optocoupler

Linear Technology Corporation has introduced an isolated monolithic flyback switching regulator that simplifies the design of a low power isolated DC/DC converter.

No opto-isolator, third winding or signal transformer is required for feedback since the output voltage is sensed from the primary-side flyback signal. The LT3574 operates over a 3 V to 40 V input voltage range, has a 0.65 A NPN power switch and can deliver up to 3 watts of output power, making it well suited for a wide variety of industrial, medical, telecom, datacom and automotive applications.

The LT3574 operates in boundary mode, which is a variable frequency current mode control switching scheme, 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 transformers 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 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: LT3574

  • VIN Range from 3 V to 40 V
  • Onboard 0.65 A, 60 V Integrated NPN 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

Availability and Pricing

The LT3574 is available in a small MSOP-16 package and is offered in an extended and industrial operating junction temperature range at -40 to 125 degrees C. Pricing starts at $2.76 each in 1000-piece quantities.



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