LTC3855 datasheet(33/44 Pages) LINER

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LTC3855

3855f

applicaTions inForMaTion

The power loss in R1 at the maximum input voltage is:

PLOSSR1=

(VIN(MAX) − VOUT)• VOUT

The resulting power loss for R1 is 11mW for channel 1

and 7mW for channel 2.

The sum of the sense resistor and DCR is 2.5mΩ (max)

for the RSENSE application whereas the inductor DCR for

the DCR sense application is 1.8mΩ (max). As a result of

the lower conduction losses from the switch node to VOUT,

the DCR sensing application has higher efficiency.

The power dissipation on the topside MOSFET can be

easily estimated. Choosing a Renesas RJK0305DPB

Figure 17. DCR Sense Efficiency vs RSENSE Efficiency

LOAD CURRENT (A)

3855 F17

1.2V RSENSE

1.2V DCR SENSE

1.8V RSENSE

1.8V DCR SENSE

VIN = 12V

MODE = CCM

DCR SENSE APP: SEE FIGURE 16

RSENSE APP: SEE FIGURE 19

EFFICIENCY

POWER LOSS

Figure 16. High Efficiency Dual 400kHz 1.8V/1.2V Step-Down Converter

0.1µF

40.2k

0.56µH

3.09k

1nF

150pF

0.1µF

82µF

25V

COUT1

330µF

L1, L2: VISHAY IHLP4040DZ-01, 0.56µH

M1, M3: RENESAS RJK0305DPB

M2, M4: RENESAS RJK0330DPB

20k

12.1k

VOUT1

1.8V

15A

0.1µF

0.56µH

1nF

150pF

COUT2

330µF

20k

4.99k

100k

VOUT2

1.2V

15A

TG1

TG2

BOOST1

BOOST2

SW1

SW2

BG1

BG2

SGND

PGND

FREQ

SENSE1+

SENSE2+

DIFFP

SENSE1–

SENSE2–

VFB1

VFB2

ITH1

ITH2

VIN PGOOD

INTVCC

TK/SS1

TK/SS2

VIN

4.5V TO

20V

3855 F16

EXTVCC

0.1µF

LTC3855

MODE/PLLIN

ILIM1

ITEMP1

ITEMP2

ILIM2

DIFFN

DIFFOUT

CLKOUT

RUN1

RUN2

3.09k

4.7µF

1µF

2.2Ω

10µF

25V

20k, 1%

LTC3855 Datasheet(PDF) 33 Page - Linear Technology

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