LT3574 datasheet(18/26 Pages) LINER

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LT3511

3511fa

Choose a diode that is fast and has sufficient reverse

voltage breakdown:

VREVERSE > VIN(MAX)

Example:

VREVERSE > 72V

The diode needs to handle the peak switch current of the

switch which was determined to be 0.24A. A 100V, 0.6A

diode from Diodes Inc. (BAV19W) is chosen.

Step 7: Compensation.

Compensation will be optimized towards the end of the

design procedure. Connect a resistor and capacitor from

the VC node to ground. Use a 20k resistor and a 2.2nF

capacitor.

Step 8: Select RFB and RTC Resistors.

Use the following equations to choose starting values for

RFB and RTC. Set RREF to 10k.

RFB =

VOUT + VF + 0.55V

(

) •NPS •RREF

1.2V

RREF = 10k

RTC =

RFB

NPS

Example:

RFB =

15 + 0.5+ 0.55V

(

) • 2 • 10k

1.2V

= 267k

RTC =

267k

= 133k

Step 9: Adjust RFB based on output voltage.

Power up the application with application components

connected and measure the regulated output voltage.

Readjust RFB based on the measured output voltage.

RFB(NEW) =

VOUT

VOUT(MEAS)

• RFB(OLD)

Example:

RFB(NEW) =

15V

16.8V

• 267k = 237k

Step 10: Remove RTC and measure output voltage over

temperature.

Measure output voltage in a controlled temperature envi-

ronment like an oven to determine the output temperature

coefficient. Measure output voltage at a consistent load

current and input voltage, across the temperature range

of operation. This procedure will optimize line and load

regulation over temperature.

Calculate the temperature coefficient of VOUT:

ΔVOUT

ΔTemp

VOUT(HOT) – VOUT(COLD)

THOT(°C) – TCOLD(°C)

Example:

VOUT measured at 100mA and 48VIN

ΔVOUT

ΔTemp

15.70V – 15.37V

125°C – –50°C

(

)

= 1.9mV/°C

applicaTions inForMaTion

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