L

Lmax

OUTmax

I

I

I

2

D

=

´

OUT

IN

L

OUT

V

1

V

I

V

L

f

-

D =

´

´

TPS62290, TPS62291, TPS62293

SLVS764F – JUNE 2007 – REVISED JANUARY 2016

www.ti.com

9.2.2.2 Output Filter Design (Inductor and Output Capacitor)

The TPS6229x is designed to operate with inductors in the range of 1.5

μH to 4.7 μH and with output capacitors

in the range of 4.7

μF to 22 μF. The part is optimized for operation with a 2.2-μH inductor and 10-μF output

capacitor.

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

conditions. For stable operation, the L and C values of the output filter may not fall below 1-

μH effective

inductance and 3.5-

μF effective capacitance.

9.2.2.2.1

Inductor Selection

The inductor value has a direct effect on the ripple current. The selected inductor has to be rated for its DC

resistance and saturation current. The inductor ripple current (

The inductor selection has also impact on the output voltage ripple in PFM mode. Higher inductor values will lead

to lower output voltage ripple and higher PFM frequency, lower inductor values will lead to a higher output

voltage ripple but lower PFM frequency.

Equation 2 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

recommended because during heavy load transient the inductor current will rise above the calculated value.

(2)

where

•

f = Switching frequency (2.25 MHz typical)

•

L = Inductor value

•

•

(3)

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

corresponding converter.

Accepting larger values of ripple current allows the use of low inductance values, but results in higher output

voltage ripple, greater core losses, and lower output current capability.

The total losses of the coil have a strong impact on the efficiency of the DC/DC conversion and consist of both

•

The losses in the core material (magnetic hysteresis loss, especially at high switching frequencies)

•

Additional losses in the conductor from the skin effect (current displacement at high frequencies)

•

Magnetic field losses of the neighboring windings (proximity effect)

•

Radiation losses

Table 2. List of Inductors

INDUCTOR TYPE

SUPPLIER

3 × 3 × 1.5

LPS3015

Coilcraft

3 x 3 x 1.5

LQH3NPN2R2NM0

MURATA

3.2 x 2.6 x 1.2

MIPSA3226D2R2

FDK

9.2.2.2.2

Output Capacitor Selection

The advanced fast-response voltage mode control scheme of the TPS6229x allows the use of tiny ceramic

capacitors. Ceramic capacitors with low ESR values have the lowest output voltage ripple and are

recommended. The output capacitor requires either an X7R or X5R dielectric. Y5V and Z5U dielectric capacitors,

aside from their wide variation in capacitance over temperature, become resistive at high frequencies.

12

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