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LTC3633

3633f

APPLICATIONS INFORMATION

A 47μF ceramic capacitor should be sufﬁcient for channel

1. Solving the same equation for channel 2 (using 5% of

VOUT for VDROOP) results in 27μF of capacitance (22μF is

the closest standard value).

CIN should be sized for a maximum current rating of:

RMS =

−

()

1 8

13 2

1 8

13 2

Solving this equation for channel 2 results in an RMS

input current of 1.3A. Decoupling each VIN input with

a 47μF ceramic capacitor should be adequate for most

applications.

Lastly, the feedback resistors must be chosen. Picking R1

and R3 to be 12.1k, R2 and R4 are calculated to be:

R2 = (12.1k) •

1.8V

0.6V

–1 = 24.2k

R4 = (12.1k) •

3.3V

0.6V

–1 = 54.5k

The ﬁnal circuit is shown in Figure 8.

RUN1

RUN2

TRACKSS2

PGOOD2

LTC3633

BOOST2

3633 F08

0.1μF

1μH

54.9k

12.1k

SW2

VON2

VIN2

VIN1

VFB2

PHMODE

TRACKSS1

PGOOD1

BOOST1

SW1

VON1

VFB1

COUT2

22μF

VOUT2

3.3V AT 3A

0.1μF

0.68μH

24.3k

12.1k

COUT1

47μF

VOUT1

1.8V AT 3A

VIN

12V

CIN

47μF

×2

162k

MODE/SYNC

ITH1

ITH2

V2P5

INTVCC

2.2μF

PGND

SGND

Figure 8. Design Example Circuit

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