LTC3415 datasheet(26/36 Pages) LINER

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LTC3613

3613fa

APPLICATIONS INFORMATION

Design Example

Consider a step-down converter with VIN = 6V to 24V, VOUT

= 1.2V, IOUT(MAX) = 15A, and f = 350kHz (see Figure 9).

The regulated output voltage is determined by:

VOUT =0.6V • 1+

RFB2

RFB1

⎛

⎝⎜

⎞

⎠⎟

Using a 20k resistor from VOSNS+ to VOSNS–, the top

feedback resistor is also 20k.

The frequency is programmed by:

RT kΩ

[]=

41550

fkHz

[]

–2.2=

41550

350

–2.2

≈116.5k

Select the nearest standard value of 115k.

The minimum on-time occurs for maximum VINandshould

be greater than 65ns, which is the best that the LTC3613

can achieve. The minimum on-time for this application is:

tON(MIN)=

VOUT

VIN(MAX) • f

1.2V

24V

•350kHz

≈143ns

Set the inductor value to give 40% ripple current at maxi-

mum VIN:

1.2V

350kHz

• 40%•15A

• 1–

1.2V

24V

⎛

⎝⎜

⎞

⎠⎟ ≈

0.54μH

Select 0.56μH, which is the nearest standard value.

PVIN

SVIN

VOUT

PGOOD

RUN

VRNG

SENSE–

SENSE+

RPGD

100k

INTVCC

RITH

28k

115k

RDCR

3.09k

LTC3613

RFB2

20k

RFB1

20k

COUT1

330μF

2.5V

×2

COUT2

100μF

×2

0.56μH

CSS

0.1μF

RDIV1

52.3k

RDIV2

10k

CITH1

220pF

CITH2 100pF

3613 F10

VIN

6V TO 24V

VOUT

1.2V

15A

CDCR

0.1μF

CB 0.1μF

CVCC

4.7μF

CIN1: SANYO 25SVPD82M

COUT1: SANYO 2R5TPE330M9

DB: CENTRAL CMDSH-3

L1: VISHAY IHLP4040DZ-056μH

TRACK/SS

ITH

MODE/PLLIN

EXTVCC

SGND

BOOST

INTVCC

PGND

VOSNS

–

CIN2

10μF

CIN1

82μF

25V

350kHz

LOAD CURRENT (A)

0.1

100

3613 F10a

VIN = 12V

VOUT = 1.2V

PULSE-SKIPPING

MODE

FORCED

CONTINUOUS

MODE

Figure 9. 1.2V, 15A, 350kHz Step-Down Converter

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