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LTC3601

3601f

Design Example

As a design example, consider using the LTC3601 in an

application with the following speciﬁcations:

VIN = 12V, VOUT = 1.8V, IOUT(MAX) = 1.5A, IOUT(MIN) =

10mA, f = 1MHz

Because efﬁciency is important at both high and low load

currents, Burst Mode operation is selected.

First, the correct RRT resistor value for 1MHz switching

frequency must be chosen. Based on the equation dis-

cussed earlier, RRT should be 324k.

Next, determine the inductor value for approximately 40%

ripple current using:

L =

1.8V

1MHz •600mA

1– 1.8V

12V

2.55μH

A standard value 2.2μH inductor will work well for this

application.

Next, COUT is selected based on the required output

transient performance and the required ESR to satisfy

the output voltage ripple. For this design, a 22μF ceramic

capacitor will be used.

CIN should be sized for a maximum current rating of:

IRMS = 1.5A

1.8V 12V – 1.8V

(

)

12V

0.54A

Decoupling the VIN pins with a 22μF ceramic capacitor

should be adequate for most applications. A 0.1μF boost

capacitor should also work for most applications.

To save board space the ITH pin is connected to the INTVCC

pin to select an internal compensation network.

The PGOOD pin is connected to VIN through a 100k

resistor.

Figure 7. 1.8V, 1.5A Regulator at 1MHz

APPLICATIONS INFORMATION

VIN

MODE/SYNC

RUN

INTVCC

PGOOD

ITH

LTC3601

PGND

SGND

BOOST

VON

TRACK

2.2μF

CFWD

10pF

0.1μF

COUT

47μF

VOUT

1.8V

1.5A

80k

40k

100k

324k

CIN: TDK C3225X5R1C226M

COUT: TDK C3225X5R0J476M

L1: VISHAY IHLP2020BZER2R2M01

3601 F05

2.2μH

CIN

22μF

VIN

4V TO 15V

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