c

1

=

= 50kHz

2

(1 H

10 F)

f

p

´

´

´

1 *

Vout

Vin

L

ƒ

I

2

TLV62065

www.ti.com

SLVSAC4 – NOVEMBER 2010

OUTPUT FILTER DESIGN (INDUCTOR AND OUTPUT CAPACITOR)

The internal compensation network of TLV62065 is optimized for a LC output filter with a corner frequency of:

The part operates with nominal inductors of 1.0µH to 1.2 µH and with 10µF to 22µF small X5R and X7R ceramic

capacitors. Please refer to the lists of inductors and capacitors. The part is optimized for a 1.0µH inductor and

10µF output capacitor.

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 (

Equation 1 calculates the maximum inductor current in PWM mode under static load conditions. The saturation

current of the inductor should be rated higher than the maximum inductor current as calculated with Equation 2.

This is recommended because during heavy load transient the inductor current rises above the calculated value.

(1)

(2)

With:

f = Switching Frequency (3MHz typical)

L = Inductor Value

converter.

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

INDUCTANCE m

mH

INDUCTOR TYPE

SUPPLIER

3.2 x 2.5 x 1.0 max

1.0

LQM32PN (MLCC)

Murata

3.7 x 4 x 1.8 max

1.0

LQH44 (wire wound)

Murata

4.0 x 4.0 x 2.6 max

1.2

NRG4026T (wire wound)

Taiyo Yuden

3.5 x 3.7 x 1.8 max

1.2

DE3518 (wire wound)

TOKO

Output Capacitor Selection

The advanced fast-response voltage mode control scheme of the TLV62065 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 and may

not be used. For most applications a nominal 10µF or 22µF capacitor is suitable. At small ceramic capacitors, the

DC-bias effect decreases the effective capacitance. Therefore a 22µF capacitor can be used for output voltages

higher than 2V, see list of capacitors.

Copyright © 2010, Texas Instruments Incorporated

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