HIGHLIGHT MAGAZINE Special issue: Industrial Solution Kit / December 2011 Easy Isolated Flyback DC/DC Converter Design Solution Evaluation Kits To offer easy isolated flyback design solutions for the LT3748 & LT357x family of ICs and WE-FB flyback transformers, Linear Technology and Wrth Elektronik have developed evaluation kits with five different power output configurations: 1. Kit 750105: 2.5 Watt LT3574 including Flyback Transformers for 3.3V, 5V and 12V 2. Kit 750103: 7 Watt LT3573 including Flyback Transformer for 5V 3. Kit 750106: 10 Watt LT3575 including Flyback Transformers for 3.3V, 5V and 12V 4. Kit 750107: 12 Watt LT3748 including Flyback Transformers for 3.3V, 5V and 12V 5. Kit 750108: 30 Watt LT3748 including Flyback Transformers for 12V, 15V and 24V ACCURATE V WITHOUT OPTOCOUPLER OR SIGNAL TRANSFORMER OUT V IN Easy Design High Reliability Few Components V Accuracy OUT V OUT LT35XX The output voltage of all these Linear Technology parts is easily set with two external resistors and the transformer turns ratio. Over 60 additional off-the-shelf transformers from Wrth Elektronik are available for many applications, with other output voltages stocked at Farnell. NO Feedback Signal Transformer The key advantages of the evaluation kits are: Ready-made demo board / circuit / application NO Feedback Easy design with standard components Optocoupler Adjustable to different input and output voltages 1 www.linear.comSpecial issue: Industrial Solution Kit / December 2011 Isolated Monolithic Flyback Simplifies Design & Eliminates Optocoupler LT3573 V Range from 3V to 40V IN Onboard 1.25A, 60V Integrated NPN Power Switch No Transformer, Third Winding or Opto-Isolator Required for Feedback Current Mode Control Boundar y Mode Operation V Set with Two External Resistors OUT Programmable Soft-Start Programmable Under voltage Lockout Output Voltage Temperature Compensation Adjustable Current Limit The LT3573 is an isolated monolithic flyback switching output load current in a typical application. Boundary mode regulator with an integrated 1.25A NPN power switch. This operation also permits the use of a smaller transformer when device significantly simplifies the design of a flyback converter compared to equivalent continuous conduction mode designs. since it does not require a third winding or optoisolator and can The output voltage is easily set by two external resistors. sense the output voltage directly from the primary side flyback The LT3573 has additional features that include an onboard waveform. The LT3573 operates over an input voltage range of LDO, programmable soft start, undervoltage lockout, adjustable 3V to 40V at output power levels up to 7 watts, and can be used current limit and output voltage temperature compensation. in a wide variety of industrial, medical, datacom and automotive The LT3573 is available in a small thermally enhanced MSOP- applications requiring isolated power. 16 package and is offered in an extended and industrial operating The LT3573 operates in boundary mode, which is a variable junction temperature range at -40C to 125C. frequency current mode switching scheme, resulting in a total regulation band of 5% over a wide input voltage range and More info: www.linear.com/3573 Low Power Isolated Monolithic Flyback Switching Regulator Simplifies Design & Eliminates Optocoupler LT3574 V Range from 3V to 40V The LT3574 is an isolated monolithic flyback switching regulator IN that signicfi antly simpliefi s the design of a low power isolated DC/ Onboard 0.65A, 60V Integrated NPN Power Switch DC converter. No opto-isolator, third winding or signal transformer No Transformer, Third Winding or Opto-Isolator Required for Feedback is required for feedback since the output voltage is sensed from Current Mode Control the primary-side flyback signal. The LT3574 operates over a 3V Boundar y Mode Operation to 40V input voltage range, has a 0.65A NPN power switch and can deliver up to 3 watts of output power, making it well suited V Set with Two External Resistors OUT for a wide variety of industrial, medical, telecom, datacom and Off-the-Shelf Transformers automotive applications. Programmable Soft-Start The LT3574 operates in boundary mode, which is a variable frequency current mode control switching scheme, resulting in Programmable Under voltage Lockout 5% regulation over the full line, load and temperature range. Output Voltage Temperature Compensation Boundary mode also permits the use of a smaller transformer Adjustable Current Limit 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 identified in the data sheet 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. The LT3574 is available in a small MSOP-16 package and is offered in an extended and industrial operating junction temperature range at -40C to 125C. More info: www.linear.com/3574 2