(

)

f

OUT

IN max

RIPPLE1

MIN

SW

V

V

1

14

3.3

1

I

D

0.236

0.513 A

L1

8.2 H

600 kHz

-

-

»

´

´

=

´

´

=

m

(

)

f

OUT

IN max

RIPPLE2

MIN

SW

V

V

1

14

1.2

1

I

D

0.086

0.556A

L2

3.3 H

600 kHz

-

-

»

´

´

=

´

´

=

m

(

)

(

)

(

)

(

)

(

)

2

2

2

2

2

2

1

1

1

RIPPLE

RIPPLE

L rms

L avg

OUT max

12

12

12

I

I

I

I

I

1.5

0.513

A

1.51A

=

+

»

+

=

+

=

(

)

(

)

(

)

(

)

(

)

2

2

2

2

2

2

1

1

1

RIPPLE

RIPPLE

L rms

L avg

OUT max

12

12

12

I

I

I

I

I

2.5

0.556

A

2.51A

=

+

»

+

=

+

=

(

)

(

)

1

1

RIPPLE

L peak

OUT max

2

2

I

I

I

1.5 A

0.513A

1.76 A

»

+

=

+

=

(

)

(

)

1

1

RIPPLE

L peak

OUT max

2

2

I

I

I

2.5 A

0.556A

2.78 A

»

+

=

+

=

(

)

(

)

(

)

2

2

TRAN max

OUT1 min

OUT

OVER

I

L

1A

8.2 H

C

12.4 F

3.3 V

0.2 V

V

V

´

´

m

=

=

=

m

´

´

(

)

(

)

(

)

2

2

TRAN m ax

OUT 2 m in

OUT

OVER

I

L

1A

3.3

H

C

13.7

F

1.2 V

0.2 V

V

V

´

´

m

=

=

=

m

´

´

f

RIPPLE

RIPPLE(total)

OUT

SW

MAX

RIPPLE

I

0.513 A

V

0.050 V

8 C

8 12.4 F 600kHz

ESR

0.081

I

0.513 A

æ

ö

æ

ö

-

-

ç

÷

ç

÷

´

´

´

m ´

è

ø

è

ø

=

=

=

W

f

RIPPLE

RIPPLE(total)

OUT

SW

MAX

RIPPLE

I

0.556 A

V

0.024 V

8 C

8 13.7 F 600kHz

ESR

0.028

I

0.556 A

æ

ö

æ

ö

-

-

ç

÷

ç

÷

´

´

´

m ´

è

ø

è

ø

=

=

=

W

TPS54290, TPS54291, TPS54292

SLUS973 – OCTOBER 2009

www.ti.com

(22)

(23)

The RMS current through the inductor is approximated by Equation 24 and Equation 25.

(24)

(25)

A DC current with 30% peak-to-peak ripple has an RMS current approximately 0.4% above the average current.

The peak inductor current is estimated by Equation 26 and Equation 27.

(26)

(27)

A 8.2-µH inductor with a minimum RMS current rating of 1.51 A and minimum saturation current rating of 3.7 A

must be selected. A Coilcraft MSS1048-822ML 8.2-µH, 4.38-A inductor is chosen for Channel 1 and a Coilcraft

MSS1048-332 3.3-µH inductor is chosen for Channel 2.

Output Capacitor Selection

Output capacitors are selected to support load transients and output ripple current. The minimum output

capacitance to meet the transient specification is given by Equation 28 and Equation 29.

(28)

(29)

The maximum ESR to meet the ripple specification is given by Equation 30 and Equation 31.

(30)

(31)

A single 22-µF ceramic capacitor with approximately 2.5 m

Ω of ESR is selected to provide sufficient margin for

capacitance loss due to DC voltage bias.

Input Capacitor Selection

A minimum 10-µF ceramic input capacitor on each PVDD pin is recommended. The ceramic capacitor must

handle the RMS ripple current in the input capacitor.

The RMS current in the input capacitors is estimated by Equation 32 and Equation 33.

22

Submit Documentation Feedback

Copyright © 2009, Texas Instruments Incorporated

Product Folder Link(s) :TPS54290 TPS54291 TPS54292