LTC3853_15 datasheet(29/36 Pages) LINER

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LTC3853

3853fc

For more information www.linear.com/LTC3853

Channel 1 will have ~2.3A (46%) ripple, and both channel

2 and channel 3 will have ~1.75A (35%) ripple. The peak

inductor current will be the maximum DC value plus one-

half the ripple current, or 6.15A for channel 1 and 5.88A

for channels 2 and 3.

With ILIM high, the equivalent RSENSE resistor value can be

calculated by using the minimum value for the maximum

current sense threshold (65mV).

RSENSE(EQUIV) =

VSENSE(MIN)

ILOAD(MAX) +

∆IL(NOM)

65mV

1.2 • 5A

∆IL(MAX)









≅ 9mΩ

The 1.2 factor adds margin for component variation and

overcurrent headroom during full load transients.

TheequivalentRSENSEisthesameforchannels1,2and3.

The Vishay IHLP2525CZER3R3M01 (30mΩ DCRMAX at

20°C) and IHLP2525CZER1R5M01 (15mΩ DCRMAX at

20°C,)arechosen.At100°C,theestimatedmaximumDCR

values are 39.6mV and 19.8mV. The divider ratios are:

RD =

RSENSE(EQUIV)

DCRMAX at TL(MAX)

Ω

39.6m

Ω

= 0.23;

and

Ω

19.8m

Ω

≅ 0.45

For each channel, 0.1µF is selected for C1.

R1||R2

(DCRMAX at 20°C)•C1

3.3

µH

30m

Ω • 0.1µF

= 1100Ω and

1.5

µH

15m

Ω • 0.1µF

= 1000Ω

APPLICATIONS INFORMATION

Figure 13. High Efficiency Triple 5V/3.3V/1.2V Step-Down Converter

TG1

TG2

BOOST1,2,3

SW1

SW2

BG1

BG2

SENSE1+

SENSE2+

SENSE1–

SENSE2–

VFB1

VFB2

ITH1,2,3

VIN

INTVCC

LTC3853

DRVCC12

MODE/PLLIN

20k

FREQ/PLLFLTR

ILIM

PGND

PGOOD12

SGND

EXTVCC

TK/SS1,2,3

VFB3

SENSE3–

SENSE3+

SW3

TG3

BG3

RUN1,2,3

PGOOD3

4.75k

1430

20k

3.16k

1nF

63.4k

4.7µF

10k

INTVCC

VOUT1

VOUT2

3.3V

20k

3853 F13

2.43k

4.75k

VOUT3

1.2V

VIN

7V TO 20V

CITH1,2,3

RITH1,2,3

0.1µF

330µF

10V

M1, M2, M3: Si4816BDY

CHANNEL 1: RITH1 = 15k, CITH1 = 1.5nF, CP1 = 220pF

CHANNEL 2: RITH2 = 18k, CITH2 = 1.5nF, CP2 = 220pF

CHANNEL 3: RITH3 = 10k, CITH3 = 1.5nF, CP3 = 330pF

FOR CHANNEL 3, 0.068µF WAS SUBSTITUTED FOR 0.1µF AND 2.43k WAS SUBSTITUTED

FOR 2.21k TO MEET MINIMUM 15mV RIPPLE AT SENSE INPUT REQUIREMENT

CP1,2,3

22µF

50V

CSS1,2,3

0.1µF

10pF

1430

3.3µH

1.5µH

CB1,2,3 0.1µF

SW1,2,3

DB1,2,3

0.068µF

1.82k

330µF

10k

105k

10pF

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