LT3574 datasheet(19/24 Pages) LINER

Part #	LT3574

Description	100VIN Micropower Isolated Flyback Converter with 150V/260mA Switch

PDF	24 Pages

Scroll/Zoom	100%

Manufacturer	LINER [Linear Technology]

Direct Link	http://www.linear.com

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19 / 24 page

LT8300

8300f

applicaTions inForMaTion

Step 7: Select the EN/UVLO Resistors.

Determinetheamountofhysteresisrequiredandcalculate

R1 resistor value:

VIN(HYS) = 2.5µA • R1

Example:

Choose 2.5V of hysteresis,

R1 = 1M

Determine the UVLO thresholds and calculate R2 resistor

value:

VIN(UVLO+) =

1.239V •(R1

+R2)

+ 2.5µA •R1

Example:

Set VIN UVLO rising threshold to 34.5V,

R2 = 40.2k

VIN(UVLO+) = 34.1V

VIN(UVLO–) = 31.6V

Step 8: Ensure minimum load.

The theoretical minimum load can be approximately

estimated as:

ILOAD(MIN) =

300µH •(52mA)2 • 7.5kHz

2 • 12V

= 0.25mA

Remember to check the minimum load requirement in real

application. The minimum load occurs at the point where

the output voltage begins to climb up as the converter

delivers more energy than what is consumed at the out-

put. The real minimum load for this application is about

0.6mA, 0.5% of 120mA maximum load. In this example,

a 20k resistor is selected as the minimum load.

LT3574 Datasheet(PDF) 19 Page - Linear Technology