LTC3124 datasheet(16/28 Pages) LINER

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LTC3124

3124f

For more information www.linear.com/LTC3124

APPLICATIONS INFORMATION

SCHOTTKY DIODE

Although it is not required, adding a Schottky diode from

both SW pins to VOUTcanimprovetheconverterefficiency

by up to 4%. Note that this defeats the output disconnect

and short-circuit protection features of the LTC3124.

COMPONENT SELECTION

Inductor Selection

The LTC3124 can utilize small inductors due to its capa-

bility of setting a fast (up to 3MHz) switching frequency.

Larger values of inductance will allow slightly greater

output current capability by reducing the inductor ripple

current. To design a stable converter the range of induc-

tance values is bounded by the targeted magnitude of the

internal slope compensation and is inversely proportional

to the switching frequency. The Inductor selection for the

LTC3124 has the following bounds:

µH

>L >

µH

The inductor peak-to-peak ripple current is given by the

following equation:

Ripple A

( )=

VIN • VOUT – VIN

(

)

f •L • VOUT

where:

L = Inductor Value in μH

f = Switching Frequency in MHz of One Phase

The inductor ripple current is a maximum at the minimum

inductor value. Substituting 3/f for the inductor value in

the above equation yields the following:

RippleMAX A

( )=

VIN • VOUT – VIN

(

)

3• VOUT

A reasonable operating range for the inductor ripple cur-

rent is typically 10% to 40% of the maximum inductor

current. High frequency ferrite core inductor materials

reduce frequency dependent power losses compared to

cheaper powdered iron types, improving efficiency. The

inductor should have low DCR (series resistance of the

windings) to reduce the I2R power losses, and must be

able to support the peak inductor current without saturat-

ing. Molded chokes and most chip inductors usually do

not have enough core area to support the peak inductor

currents of 3A to 4A seen on the LTC3124. To minimize

radiated noise, use a shielded inductor.

See Table 2 for suggested components and suppliers.

Table 2. Recommended Inductors

PART NUMBER

VALUE

(µH)

DCR

(mΩ)

ISAT

(A)

SIZE (mm)

× L × H

Coilcraft XFL4020-102ME

5.4

4.3

× 4.3 × 2.1

Coilcraft MSS7341T-332NL

3.3

3.7

7.3

× 7.3 × 4.1

Coilcraft XAL5030-332ME

3.3

8.7

5.3

× 5.3 × 3.1

Coilcraft XAL5030-472ME

4.7

6.7

5.3

× 5.3 × 3.1

Coilcraft XAL5050-562ME

5.6

6.3

5.3

× 5.3 × 5.1

Coilcraft XAL6060-223ME

5.6

6.3

× 6.3 × 6.1

Coilcraft MSS1260T-333ML

4.34 12.3 × 12.3 × 6.2

Coiltronics SD53-1R1-R

1.1

4.8

5.2

× 5.2 × 3

Coiltronics DR74-4R7-R

4.7

4.37 7.6 × 7.6 × 4.35

Coiltronics DR125-330-R

3.84

12.5

× 12.5 × 6

Coiltronics DR127-470-R

5.28

12.5

× 12.5 × 8

Sumida CDR7D28MNNP-1R2NC

1.2

5.9

7.6

× 7.6 × 3

Sumida CDMC6D28NP-3R3MC

3.3

7.25

× 6.7 × 3

Taiyo-Yuden NR5040T3R3N

3.3

3.8

× 5 × 4

TDK LTF5022T-1R2N4R2-LC

1.2

4.3

× 5.2 × 2.2

TDK SPM6530T-3R3M

3.3

6.8

7.1

× 6.5 × 3

TDK VLP8040T-4R7M

4.7

4.4

× 7.7 × 4

Würth WE-LHMI 74437324010

4.45

× 4.06 × 1.8

Würth WE-PD 7447789002

2.2

4.8

7.3

× 7.3 × 3.2

Würth WE-PD 7447779002

Würth WE-PD 7447789003

2.2

3.3

4.2

7.3

× 7.3 × 4.5

7.3

× 7.3 × 3.2

Würth WE-PD 7447789004

4.7

3.9

7.3

× 7.3 × 3.2

Würth WE-HCI 7443251000

8.5

× 10 × 5

Würth WE-PD 744770122

× 12 × 8

Würth WE-PD 744770133

3.6

× 12 × 8

Würth WE-PD 7447709470

4.5

× 12 × 10

Output and Input Capacitor Selection

Low ESR (equivalent series resistance) capacitors should

be used to minimize the output voltage ripple. Multilayer

ceramic capacitors are an excellent choice as they have

extremely low ESR and are available in small footprints.

X5R and X7R dielectric materials are preferred for their

ability to maintain capacitance over wide voltage and tem-

perature ranges. Y5V types should not be used. Although

ceramic capacitors are recommended, low ESR tantalum

capacitors may be used as well.

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