LT3757 datasheet(18/24 Pages) AD

18 / 24 page

LT8300

Rev. A

For more information www.analog.com

APPLICATIONS INFORMATION

Step 7: Select the EN/UVLO Resistors.

Determine the amount of hysteresis required and calcu-

late 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 esti-

mated 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.

LT3757 Datasheet(PDF) 18 Page - Analog Devices