2

•Onboard1.25A,60VIntegratedNPNPowerSwitch

•NoTransformer,ThirdWindingorOpto-IsolatorRequired

forFeedback

•CurrentModeControl

•BoundaryModeOperation

• ProgrammableSoft-Start

• ProgrammableUndervoltageLockout

• OutputVoltageTemperatureCompensation

•

AdjustableCurrentLimit

The LT3573 is an isolated monolithic flyback switching

regulator with an integrated 1.25A NPN power switch. This

device significantly simplifies the design of a flyback converter

since it does not require a third winding or optoisolator and can

sense the output voltage directly from the primary side flyback

waveform. The LT3573 operates over an input voltage range of

3V to 40V at output power levels up to 7 watts, and can be used

in a wide variety of industrial, medical, datacom and automotive

applications requiring isolated power.

The LT3573 operates in boundary mode, which is a variable

frequency current mode switching scheme, resulting in a total

regulation band of ±5% over a wide input voltage range and

Special issue:

Industrial Solution Kit / December 2011

output load current in a typical application. Boundary mode

operation also permits the use of a smaller transformer when

compared to equivalent continuous conduction mode designs.

The output voltage is easily set by two external resistors.

The LT3573 has additional features that include an onboard

LDO, programmable soft start, undervoltage lockout, adjustable

current limit and output voltage temperature compensation.

The LT3573 is available in a small thermally enhanced MSOP-

16 package and is offered in an extended and industrial operating

junction temperature range at -40°C to 125°C.

Low Power Isolated Monolithic Flyback Switching Regulator Simplifies Design &

• Onboard0.65A,60VIntegratedNPNPowerSwitch

• NoTransformer,ThirdWindingorOpto-IsolatorRequiredforFeedback

• CurrentModeControl

• BoundaryModeOperation

• Off-the-ShelfTransformers

• ProgrammableSoft-Start

• ProgrammableUndervoltageLockout

• OutputVoltageTemperatureCompensation

• AdjustableCurrentLimit

The LT3574 is an isolated monolithic flyback switching regulator

that significantly 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 3V

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

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% 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

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 -40°C to 125°C.