TPS65014 datasheet(49/53 Pages) TI

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DESIGN PROCEDURE

Inductor Selection for the Main and the Core Converter

DIL + VO

1–

(3)

L(max) +

O(max) )

DIL

(4)

Output Capacitor Selection

TPS65014

SLVS551 – DECEMBER 2004

The main and the core converters in the TPS65014 typically use a 6.2-µH and a 10-µH output inductor,

respectively. Larger or smaller inductor values can be used to optimize the performance of the device for specific

operation conditions. The selected inductor has to be rated for its dc resistance and saturation current. The dc

resistance of the inductance influences directly the efficiency of the converter. Therefore, an inductor with lowest

dc resistance is selected for highest efficiency.

Equation 3 calculates the maximum inductor current under static load conditions. The saturation current of the

inductor should be rated higher than the maximum inductor current as calculated with Equation 3. This is needed

because during heavy load transient, the inductor current rises above the value calculated under Equation 3.

with:

•

f = Switching frequency (1.25 MHz typical)

•

L = Inductor value

•

∆I

L= Peak-to-peak inductor ripple current

•

ILmax = Maximum inductor current

The highest inductor current occurs at maximum VI.

Open core inductors have a soft saturation characteristic, and they can usually handle higher inductor currents

versus a comparable shielded inductor.

A more conservative approach is to select the inductor current rating just for the maximum switch current of the

TPS65014 (2 A for the main converter and 0.8 A for the core converter). Keep in mind that the core material from

inductor to inductor differs and has an impact on the efficiency especially at high switching frequencies.

See Table 4 and the typical applications for possible inductors

Table 4. Tested Inductors

DEVICE

INDUCTOR VALUE

DIMENSIONS

COMPONENT SUPPLIER

10 µH

6 mm

× 6 mm × 2 mm

Sumida CDRH5D18-100

Core converter

10 µH

5 mm

× 5 mm × 3 mm

Sumida CDRH4D28-100

4.7 µH

5,5 mm

× 6,6 mm x 1 mm

Coilcraft LPO1704-472M

4.7 µH

5 mm

× 5 mm × 3 mm

Sumida CDRH4D28C-4.7

4.7 µH

5,2 mm

× 5,2 mm × 2,5 mm

Coiltronics SD25-4R7

Main converter

5.3 µH

5,7 mm

× 5,7 mm × 3 mm

Sumida CDRH5D28-5R3

6.2 µH

5,7 mm

× 5,7 mm × 3 mm

Sumida CDRH5D28-6R2

6 µH

7 mm

× 7 mm × 3 mm

Sumida CDRH6D28-6R0

The advanced fast response voltage mode control scheme of the inductive converters implemented in the

TPS65014 allow the use of small ceramic capacitors with a typical value of 22 µF for the main converter and 10

µF for the core converter without having large output voltage under/overshoots during heavy load transients.

Ceramic capacitors having low ESR values have the lowest output voltage ripple and are recommended. If

required tantalum capacitors with an ESR < 100

ΩR may be used as well.

See Table 5 for recommended components.

TPS65014 Datasheet(PDF) 49 Page - Texas Instruments

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